Evaporators & Finishing

Reverse Osmosis 101+

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Ohio Maple Days 2022 did not disappoint.  The food was fantastic, the vendor room crowded, and the presenters shared a wealth of knowledge of expertise across a wide range of subjects.  Joel Oelke, Regional Sales Manager with Leader Evaporator/H2O Innovation, shared an encyclopedic wealth of knowledge regarding reverse osmosis leading up to the lunch hour.  Before we get into a few highlights, be sure to mark your calendars for next year’s conference December 8th and 9th!

At its simplest, reverse osmosis is a process by which sap is passed through a membrane to remove water thereby concentrating sugar.  The pure water pulled out of the sap is referred to as permeate.  The increasingly sugary solution – concentrate.  The benefits are obvious – it saves space on numerous fronts and greatly improves efficiency at the evaporator by reducing time, fuel, and labor.  While the list of pros is long, suffice it to say – reverse osmosis is one of the biggest technological revolutions the maple industry has experienced in the last 100 years.

While reverse osmosis is a true game changer for maple producers, the technology is also one of the most complex and expensive pieces of equipment in the sugarhouse.  It is easy to become intimidated by what’s necessary to implement and maintain a unit, and mistakes chalked up to the “school of hard knocks” can be expensive.  Here are just 5 rules of thumb that I pulled from Joel’s presentation to share in this article.

#1 – RO’s efficiency rating (how many gallons can a unit process per hour) is given at a solution temperature of 55 degrees Fahrenheit.  Because sap is kept at cooler temperatures to ensure syrup quality, you need to factor the lower temperature into your unit’s efficiency rating.  This is especially important to consider if you are shopping for a new RO unit.  Here’s a simple figure to calibrate your RO’s operating efficiency.  If you purchase a unit rated at 600 gallons per hour but expect to run sap at an average temperature of 40 F, you can multiply 600 by an efficiency downgrade of 0.75 (or 75%) and expect a 450 gallon per hour operating rate.

#2 – A second factor influencing RO efficiency is the concentrate level you are trying to achieve assuming you start around 2 Brix.  The more you want to concentrate your sap, the less efficient your unit will be.  Let’s continue with the example we started above in italics.  If you want to take 2% sap to 8% concentrate, your RO unit will run at the temperature-corrected peak of efficiency and achieve your calibrated 450 gallons per hour rate.  However, if you concentrated to something higher, say a 12% level, your operation would get dinged with an additional 30% loss in efficiency.  Here’s what the math would reveal – 450 gallons per hour multiplied by 0.70 = 315 gallons per hour.  Below is another figure to help you calculate the efficiency factor of concentration.  Remember, you must factor in both penalties – sap temperature and concentrate level – to properly estimate your efficiency rating.  And this all assumes you are running a clean, properly-maintained RO unit!

#3 – The desugaring, rinsing, and washing cycles are what keep your expensive reverse osmosis investment operating at the peak of performance.  Long story short – each cycle is critical to maintaining your unit.  And do not – especially in the wash cycle – generalize across all RO units.  Specific models and manufacturers use different membranes which are tailored to different types of soaps and chemicals as well as amounts of each.  Consulting the manuals and consulting with your RO manufacturer reps – just like Joel – is best practice for getting maximum life and performance out of your reverse osmosis technology.

#4 – Don’t let your improved efficiency get you in to trouble.  What I mean is this – sap that goes through a reverse osmosis unit comes out as warmer concentrate.  So, A) the process of reverse osmosis physically warms the concentrate above the temperature that it went in the machine, and B) you aren’t concentrating just sugar with an RO unit, you are concentrating everything – including microbes and bacteria.  The warmer concentrate coupled with a denser community of “nasties” can get a producer in big trouble if the evaporator is not synced up in work flow and their facility can not properly keep concentrate cool.  Stopping short of laying out any specific recommendations for how to integrate and streamline your sugarhouse sap-to-syrup processing, just know that the clock is ticking extra fast once you start concentrating sap.

#5 – If you properly size, run, and maintain an reverse osmosis unit, you can expect roughly a 3-year payback on your purchase when accounting for saved fuel and labor.  A rough cost estimator predicted a $4 cost savings per finished gallon of syrup using fuel oil in a 110 gallon per hour evaporator.  Obviously there a lot of moving parts for each unique scenario, but the bottom line is this asset does not 10 years to recoup costs.

Hopefully these quick 5 points help you make sense of reverse osmosis and how you might consider incorporating or upgrading an RO unit in your sugaring operation.  Thanks for an extremely informative talk Joel!

Fall Maple Assessment – Get Ready for Next Season, Part II

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Read the first installment of our autumn mini-series “Get Ready for the Season” here.  The first article focuses mainly on the woods, and Part II sticks to the sugarhouse.

It is perfectly natural after a long hard season to put off sugarhouse cleanup and maintenance. This can be a major mistake. Getting the sugarhouse ready for the next season starts immediately after last season has concluded.  Dirty unmaintained equipment sitting around in warm weather can promote the worst of unsanitary conditions that will surely haunt you into the upcoming season.

Let’s start with storage tanks. Not everyone can afford bright shiny stainless-steel tanks that are easy to clean. Many producers substitute more affordable plastic tanks. Unfortunately, plastic tanks have earned the reputation of lowering syrup grades due to rapid microbial growth. All of the elements for rapid growth are present. The sap supplies the food and the tanks warm quickly. Where do the microbes come from? They are hiding in the porous interior of the tank. That porosity is what makes it almost impossible to thoroughly clean a plastic tank. You may get by for two or three years but sooner or later the tanks will have to be scrapped. The cost of three or four plastic tanks over a ten-year period can add up quickly. Consider the economic value of a stainless tank that should last forever if handled and maintained properly.

Reverse osmosis (RO) has revolutionized the dynamics of the maple syrup industry. For the commercial producer, the RO has drastically slashed labor and fuel expenses. When it comes to maintenance, the most critical element is maintaining the primary filter or membrane. Membranes that are not maintained properly can be severely damaged. Damage can lead to the passing of sugar into the permeate tank. This results in a hidden loss of profits going down the drain. Always check your permeate for abnormally high sugar content. Washes of both soap and acid are used in the cleaning process followed by an extensive permeate rinse. A properly maintained membrane should last for many years. Another critical but oft overlooked issue are increased levels of chemicals being discharged from the sugarhouse. When you are using an RO, you are discharging thousands of gallons of liquid through your sugarhouse drains. You are also discharging acids and soaps through the same drain. If possible, neutralize the chemicals by bringing both acids and soaps back to a neutral 7.0 pH before you flush them down the drain. Neutralizing agents are readily available from your maple dealer.

Producers tend to overlook where and how they store there concentrate before boiling. When you concentrate sap, you are creating the perfect storm for a microbial outbreak. You are doubling, and in some cases tripling, the amount of sugar in the tank. When you run the sap through an RO you also boost the concentrated sap’s temperature by at least 20 degrees Fahrenheit. Assuming the concentrated sap is housed in a relatively warm sugarhouse, it makes no difference if you are using a stainless or plastic tank, microbial populations always explode in concentrated sap. The first line of defense is to boil the concentrate as soon as you can to prevent grade deterioration. If you only have enough money to purchase one stainless steel tank, make the purchase for your evaporator feed tank. This is doubly true if you are concentrating with reverse osmosis.

One of the best maintained pieces of equipment in any maple operation must be the evaporator. After all it is the center piece of most sugarhouses. Producers tend to take pride in how their evaporator looks inside and out. Here are a few things to consider before you start the season. Make sure all of the fittings and gaskets are functioning properly. It is good idea to do a test boil before using. You do not want to waste sap or concentrate if there is a malfunction. During the season, always start each day with clean niter-free syrup pans. Do not let niter build up. Excessive niter can cause a pan to overheat and even burn. Make sure you are using defoamer properly and in the proper place. If you are going to be shut down for a long time due to a warm spell, plan on draining your pans to prevent microbial buildup. Attempting to keep the liquid on the evaporator will only lead to contamination of fresh sap when it arrives and the production of poor-quality syrup. In a freezeout situation, make sure to inspect your pans to make sure they are not freezing solid. If they are, light a fire and thaw out your pans so they do not break. Again, emptying the pans is not a bad idea. Along with your evaporator make sure your filter press and auto-draw off are functioning properly. Improper maintenance of your evaporating and filtering equipment can result in the production of poor-quality syrup that will cost you money in the long run.

After the season, make sure everything is cleaned and stored properly. There are many ways to clean an evaporator and it comes down what works for you. Avoid using any kind of detergent in the cleaning process. Hot water and elbow grease wins out every time. At the end of the season, make sure your syrup is stored properly. There is nothing worse than opening a barrel of your top grade, only to find out it has spoiled. Syrup is best stored in a location where it stays below 70-degree Fahrenheit. Even though you hot pack your syrup it is wise to roll the drums, if possible, several times during the offseason. This agitation helps eliminate moisture condensation from collecting at the top of the drums due to temperature fluctuations.

If you are planning to upgrade your sugarhouse, keep in mind that this is the best time to make sure your facility can pass a state or federal inspection. All of the rules and regulations are available online through OSU Extension.

You have now done a comprehensive evaluation of your sugaring operation. What are your most cost-effective “low hanging fruit” items? Act now – season will be here before you know it.

Maple Assistance Opportunity through EQIP

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The Environmental Quality Incentive Program, EQIP for short, provides financial and technical assistance to agricultural producers and woodland managers to combat environmental concerns and provide natural resources benefits.  Maple Producers should be excited to know that several maple practices are now eligible under EQIP.

How does EQIP work in the first place?

EQIP is a voluntary program, and contracts are available for a single year ranging up to a full decade.  The list of EQIP practices is long.  If you can imagine an environmental issue facing a farmer or woodland owner, you can safely bet there is an EQIP practice (or 3!) to meet that need.  Successful applicants to receive EQIP assistance paid at either a 75% or 90% rate to implement the recommended activity on their property.  Historically Underserved applicants, which includes Beginning Farmers, Limited Resource Farmers, Socially Disadvantaged Farmers, and Veteran Farmers, can tap into the higher 90% rate.

How does maple fit in to EQIP?

There is no set-aside pot of money allocated only for maple producers.  To improve your chances to get maple-related assistance, you should couple forestry- or wildlife-related practices.  Think tree or shrub plantings, managing grapevines or invasive species, or improving your woods through a Timber Stand Improvement (TSI) cut for just a few examples.  If you are a farmer, there are plenty of other practices to consider as well.  The more comprehensive and realistic your application to EQIP is, the better your odds of being a successful awardee.

So what are the maple-specific EQIP practices?  There are functionally 2 practices – reverse osmosis and sap preheaters that fall under Practice Code 374 – Energy Efficient Agricultural Operation.  Once you break up the size of sap preheaters into small/large and bracket RO units as small/medium/large capacity, the number of specific items actually grows to 5.  The 2 graphics below will explain more of the cost rate assistance details.

When/how do I apply?

The very first step is to determine if you are eligible to apply, and the initial process starts with establishing records with the Farm Service Agency.  Once eligibility is determined, you can proceed with your application.  All the applications are ranked against one another for funding priority.  In other words, EQIP ranks applications to ensure their dollars are going as far and as efficiently as they possibly can.

When to apply is just as important as How to apply.  The next batch of EQIP applications will be finalized and ranked on January 14th for the Fiscal Year 2022.  Though applications can be submitted year-round, any application received after mid-January will be considered in the 2023 batch of applications.

Who can help me apply?

You should contact your local NRCS service center and get in touch with the ODNR Service Forester covering your territory.

When will I find out if I got EQIP assistance?

It’s hard to know an exact date; however, once when successful applicants are notified, the final step is to sign contract documents once they are ready.

 

Don’t be discouraged if you miss the January 14th deadline, you can always be working on your application for the next Fiscal Cycle.  While there is no guarantee that maple producers will be so well-positioned to benefit from EQIP in coming years, EQIP is a wonderful program that can benefit your maple operation but in much broader ways as well.

Author: Gabe Karns
Special thanks to Gary Graham for forwarding information about the Practice Code 374 eligibility.

Choosing the Right Fuel (Evaporator Series *BONUS* Post)

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When it comes to selecting a fuel source for your evaporator, operators should choose based on efficiency, not convenience. To convert 2% sap into 66 brix syrup, 400,000 BTU are required – this is constant for all fuel sources. The two most popular fuel sources, in today’s maple world, are wood and fuel oil.  Additional choices include natural gas, liquefied petroleum (LP) gas, and various wood products such as pellets have been adapted to fuel maple evaporators.

I created the above figure based on estimates generated from the Southern Maine Renewable Fuels Institute.  Based on the statistic above – 400,000 BTU are required to produce a gallon of syrup – I derived production cost estimates for each fuel source and compared burner efficiency. Fossil fuels have a slight edge when it comes to fuel efficiency. The reason they are so efficient is based on the type of burners used and the ability to extract a higher percentage of heating units from each fuel source.

How do you choose the right fuel source for your maple operation?

The ambiance of making syrup on a roaring wood fire has never been challenged. Wood is by far the most popular fuel source for evaporators. It is readily available. And most producers look at dead wood scattered about the sugarbush as something that needs to be disposed of anyway. For that reason, the true value of wood is seldom considered. As we will see later, the value of wood is very close to the value of fuel oil when it comes to making syrup. The true value of wood is based on the dollar value of cordwood. There is an old saying “cordwood has no value until it cut and stacked.” Its value is representative of your time and labor.

A standard evaporator will produce 22 gallons of syrup from a cord of dry wood. Without the major advances in wood burning technology, most open evaporators are rated at 40-60% efficiency. Heat units are lost at multiple locations across the evaporator. You can quickly see why many producers made the shift to more efficient oil evaporators even though they now had to pay for fuel. The efficiency of a wood-fired evaporator is in the design. No matter what the design, the basic principle of operation remains the same. A wood-fired evaporator draws heat from the flame produced in the firebox. The heat consisting of flame and burning gases is drawn by air movement under the pans and out the stack. The arch is designed to pull and lift the flame up a moderate incline eventually compressing the heat into the flues of the rear pan. The heat exits the evaporator through the stack at temperatures of 600-800 degrees F. Stack dimensions must be designed correctly for proper draft. Wood needs to be placed in the evaporator to facilitate maximum heat without choking the air and dampening the flame. This usually means the firebox should not be filled to the top. You need to allow space for air to enhance the flame. The wood should be fired at regular intervals. A general recommendation is every 5 minutes.

There have been many changes in modern wood arch design that increase the overall efficiency of the evaporator. Forced air injection along with highly insulated arches and firing doors make the modern wood-fired evaporator as efficient as their oil-fired counterparts. Some are rated 85-90% percent efficient. Such high-performance levels are the result of being able to totally burn the wood that is loaded and the ability to re-burn gasses given off during the combustion process (gassification).

Fuel oil is another popular choice among maple producers, and there are several reasons for this. Fuel oil burns clean and hot and is an ideal choice for larger operations that require high volumes of fuel. This logic has been tempered in recent years with the increasing use of reverse osmosis to produce high Brix concentrate and reduce fuel demands. Efficiency is relatively high nearing 80%, and 1 gallon of syrup can be produced for under 4 gallons of fuel oil.


Bio-diesel Evaporator.

Unlike wood-fired arches, oil-fired evaporators require a minimal draft. Oil-fired arches are designed to develop radiant heat. The burner flame creates a ball of radiant heat and that heat then hovers beneath the pans. Temperatures in an oil arch can reach 1000 degrees F. The movement and intensity of the heat is controlled by a barometric damper that restricts the movement of air through the stack. The damper maintains a uniform temperature by controlling the airflow thru the evaporator. If this control device is not present, the heat can quickly be lost up the stack and the performance of the machine will be impaired. The burner nozzle size and fire rate determine the intensity of the heat. If everything is working correctly, the flame will burn cleanly and the flame ball of burning fuel oil will be suspended in the middle of the fire box never touching the sides of the arch.

Natural gas is very similar to fuel oil. In fact, the burners today are very similar in operation. Natural gas is convenient and is probably a cleaner source of fuel than oil; additionally, efficiency mirrors fuel oil. Though the original natural gas burners were often inconsistent resulting in hot and cold spots across the pans, there is now little difference in performance as compared to oil-fired evaporators. The biggest drawback is the availability of natural gas. Unlike oil that can be hauled to a remote location, gas needs to be piped in and is not readily available everywhere. If you are fortunate enough to have natural gas available, it is an excellent fuel option.


Natural Gas Evaporator.

The biggest drawback for oil and gas is the variability in cost as the oil market fluctuates. In 2020, we are living in a down cycle for oil and gas and prices are more appealing entering the 2021 syrup season. Within a few years, that could be a completely different story. Time will tell.

I would be remiss if I stopped the article there.

Regardless of what fuel source you choose for making maple syrup, the best single investment a producer can make is to add reverse osmosis to their operation. Despite the high initial cost of reverse osmosis, the cost of processing syrup is reduced significantly and the pay-off is long-term. Reverse osmosis not only allows a producer to process sap quicker, but it also opens the door to expand one’s operation. The savings on fuel are obvious. Before ROs, as reverse osmosis is commonly called, became popular the size of the operation was limited to the amount of sap that could be boiled on an evaporator. The only way to add capacity was to add evaporators, and some of the larger operations were running four, five, and even six to handle peak sap flow. Today, those same operations now employ modern RO systems with multiple membranes that can handle sap coming from thousands of taps. And using less time and space to do so. Reverse osmosis revolutionized the North America Maple Industry.

Author: Les Ober, Geauga County OSU Extension

All Things Evaporators: Part IV

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In this final post of the evaporator series, we will examine a few remaining factors to account for when considering the boiling process for maple syrup. As you will see, a few instruments enable the necessary precision to ensure a high-quality batch of syrup every time.

In case you missed them, here is Part I, Part II, and Part III of the series.

Barometric Pressure Matters

One of the biggest factors influencing the boil in an evaporator is barometric pressure. Barometric pressure and weather fronts are frequently responsible for the day-to-day erratic behavior in the way sap boils. The boiling rate is directly associated with the barometric pressure on any given day. If you experience a high barometric pressure, sap boils faster; with low barometric pressure, the boil slows. Meteorological shifts can happen several times per day, and whenever pressure fluctuates the boiling point of water (212 F) will vary. Producers must adjust their thermometer to accurately produce syrup consistently at 219 F. Make sure you calibrate your thermometer in boiling water before the start of each boil and throughout the day as needed. A thermometer will give you a ballpark reading, but to get ultra-precise and guarantee 66 Brix syrup of the highest quality, additional instruments should be utilized.

Having the Right Instruments

You will choose one of three instruments to determine your syrup density coming off the evaporator.  Only one is the best and most accurate for reading syrup straight off the evaporator. As previously stated, syrup’s finishing point is 219 Fahrenheit, 7 degrees above the boiling point of water. Because barometric pressure influences boiling point, using only a thermometer can result in inconsistent finished syrup density. One better option is to use a refractometer, but the syrup sample has to be temperature-stable and filtered to get an accurate reading. For this reason, we do not recommend using a refractometer on syrup coming directly off the evaporator for obvious and practical reasons. (Refractometers are, however, the instrument of choice for measuring the density of cooled and filtered syrup during canning).

The most recommended instrument to determine the density of hot finished syrup is the hydrometer.  A hydrometer should be floated in a sample of finished syrup that is at least 211 degrees F. Hydrometers have two lines, one for cold and one for hot. You will use the hot line for your syrup density determination straight off the evaporator. Bring the instrument up to eye level or set it on a stable object close to eye level for the most accurate reading. The hydrometers red line should float even with syrup level in the container. Most hydrometers also have two scales, one for Brix and one for Baume (Baume measures specific gravity of a solution). The Brix scale is the most popular and frequently used today. Avoid letting scale build up on the outside of the glass as it will impact the density reading, and producers should regularly validate their hydrometers for accuracy. Once you confirm finished syrup of the proper density, you will filter your syrup for clarity and to remove niter. You can then use a color comparator to determine the grade of your syrup.

Conclusion

The evaporator has become the center piece of many maple operations. It is the first thing visitors see in your sugarhouse no matter what time of year they visit.  It is also one of the most essential pieces of equipment in your operation.  After all the process of making syrup requires that we must heat maple sap to 7 degrees above the boiling point of water to produce pure maple syrup. This results in the caramelization of maple sap into maple syrup. The addition of heat to maple sap results in the amber color we desire and the maple flavor we love.

Author: Les Ober, OSU Extension Geauga County

All Things Evaporators: Part III

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Part 1 and Part 2 of our Evaporator series focused on managing the flue pans and the syrup pans in your evaporator rig. Now the focus will be on controlling two factors that can wreak havoc on the syrup-making process: foam and niter.

Controlling Foam

Foam occurs naturally during the boiling process, and foam problems become more prevalent later in the season when bacterial growth is greatest. A bad foaming issue can make it appear as though your evaporator is boiling over.

Let’s look at the practice of defoaming an evaporator. Think about the last time you boiled syrup on the stove to make candy. A pot with syrup will boil over very quickly. To prevent this, you can smear butter along the rim of the pan. On an evaporator, we do the same basic thing only on a larger scale. Foam build-up starts in the flue pan. Foam bubbles contain liquid that is being pulled away from the pan surface suspending it above the hot liquid below. This reduces the depth of liquid in the pan. Shallower liquid will boil off faster creating hot spots that show up first as areas of intensified steam. These steaming volcano-like hot spots are the first indication you may be headed for trouble. All of this can be avoided by keeping foam to a minimum. Regardless of where the hot spots are located, there are only two places to put defoamer, in the inlet corner of the flue pan and, only if needed, at the draw-off point. One of the biggest mistakes is to put defoamer randomly across the middle of the pans, especially in the syrup pan. Doing this disrupts the gradient, kills the boil, and promotes intermingling of syrup of different densities. This is the most common reason for drawing off the dreaded big batch.

Today we use commercial food-grade defoamers or organic products like canola oil to defoam a pan. There are several methods to place defoamer into the evaporator. One is to simply put it in by hand. If this method is used, the defoamer should be put into your evaporator somewhere near the rear of the flue pan. The most consistent results can be obtained by placing a precise number of drops into the flue pan every 5 to 10 minutes or every time you fire the rig. The number of drops used varies anywhere from 3 drops for small rigs up to 10 drops on larger rigs. The width of the evaporator determines the number of drops, and the rule of thumb is 1 drop for every 6-8 inches of evaporator width. Three drops in a 2-foot rig, 4-5 in a 3-foot rig, and up to 10 drops on a 6-footer would be appropriate application rates.

The biggest problem I have (and I suspect other producers as well) is remembering to place the defoamer in the flue pan because we are not using wood and not firing on regular intervals. A timer works well to remind you to keep on schedule. Other methods would be the use of a defoamer cup in the corners of the pan or injection devices that administer a precise number of drops over time. Defoamer cups work well on larger rigs where the boil in the flue pan is very aggressive.

If your syrup tastes a little oily, you are probably using too much defoamer. If you are an organic producer using organic canola oil, be especially wary of over-application. These cooking oils are not as effective as commercial defoamer and require higher application rates. Over-application can result in off flavors or a greasy feel to the syrup when tasted.

Controlling Niter

What is niter, or as the old-timers called it – sugar sand, and where does it come from?

Niter is a suspension of minerals and other solids that precipitate out of the sap during the boiling process. The amount of niter present in sap varies from season to season, from woods to woods and time of year. These suspended solids are removed during the syrup filtration process. The prevention of niter build-up is critical.

In an evaporator heat must be transferred through the thin metal surface of the pan into the liquid to create the boil. A portion of the suspended solids tend to adhere to the heated metal surface of the pan. In extreme cases, the caked niter will scorch, burn, and that excess heat will eventually buckle the metal pan. Allowing niter build-up insulates the liquid from the pan surface causing the metal surface to burn. Due to the higher concentration of solids in the sap, niter build-up tends to increase the closer you get to the draw-off point. Depending on the volume of syrup moving through the evaporator, removing niter must be done once daily or several times during a boil. As you move further away from the draw-off point, niter build-up is a lot less and the boiling action tends to break the niter down. However, all your front pans need to be cleaned and rotated on a regular basis. Starting the day with a clean syrup pan is a necessity.  Pans can be cleaned with the use of white vinegar and hot water. This is a very effective way to clean pans with a minimal amount of elbow grease.

Author: Les Ober, Geauga County OSU Extension

All Things Evaporators: Part II

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Scroll down or click under the Evaporators and Finishing Archive tab to read Part I.

Managing Your Syrup Pan

What happens in the syrup (or front) pan determines the success or failure of every producer’s season. It is here that all the standards of maple syrup quality come together. Ideally, the right density meets the right color and the right flavor. The science is using instruments to determine the exact time to draw off the syrup. The art is that sixth sense of knowing when everything is moving toward the perfect draw-off. That sixth sense is something that requires experience and is often handed down generation to generation. If the science and art come together properly, the result is golden amber maple syrup with the perfect maple flavor.

When sap transitions from the flue pans to the syrup pans, many gallons of water have already been removed leaving a sap concentration of roughly 18-19 Brix. If syrup represents 1 gallon of the remaining liquid, approximately 9 more gallons of water still need to be evaporated in the syrup pans. The speed at which this happens is relative to the size of the evaporator you are running and the quality of your fuel source. In most rigs, the transition happens quickly, and operators must devote their undivided attention to avoid problems and ensure a quality product.

Unlike flue pans, the front or syrup pan is a flat bottom designed to create a surface with even heat exchange. There are several types of front pans on the market today. Traditional drop flue evaporators were equipped with a standard reverse flow pan which allowed the operator to change the side used to draw off when niter (sugar-sand) built up. Over the years, this style of evaporator has seen modifications.

One improvement included designing the pan so that the flow can be reversed while allowing the draw-off to remain on one side. This is accomplished with a series of valves and external plumbing directing the flow of sap from one side to the other. An example of this would be the “Leader Revolution Pan.” Producers found this improvement to be helpful to avoid the movement of draw-off equipment from one side of the rig to the other.


Cross flow design on a raised flue evaporator.  Electronic floats calibrate sap depth between the back and front pans.

Another front pan configuration is the cross-flow design. Cross-flow pans are installed setting across the arch hooked in series with the draw-off near the front of the last pan. There can be anywhere from two pans on a standard rig to four pans on bigger rigs designed to handle “High Brix Concentrate”.  Because niter tends to accumulate in the draw-off pan first, that pan needs to be switched out to avoid excessive niter build-up. Most producers using this system have one or two extra pans cleaned and ready if the draw-off pan needs to be switched.

The depth of the sap in the front pan is determined by the design of the evaporator. A drop flue rig will maintain the depth set by the flue pan float, but a raised flue rig allows producers to set a separate depth in the front plan. Producers should carry approximately 2 inches of liquid across the front pans allowing syrup to boil evenly to the draw-off point. As pointed out in the first evaporator post, if hot spots develop, that area of the pan will tend to boil faster increasing the risk of burning. The trouble usually occurs when you draw off large volumes of syrup at one time. This causes the liquid level to become very uneven, you might have 2 inches in one part of the pan and only a half-inch in another.  Removing small batches more often will prevent uneven syrup levels and ensure a steady even boil.


Site gauge for monitoring sap depth on a raised flue evaporator.

It bears repeating that producers should pay close attention to bubbles in the sap. As liquid temperatures go above 219 F, the liquid will gravitate toward the hot area, localized boiling becomes more intense over the hot spot, and steam and bubbling from the more intense boil becomes more concentrated and noticeable. The result is that the sap is becoming more concentrated in the hot zone. This means the sap is becoming more concentrated in that area. As concentration increases and sap thickens to syrup, the thicker liquid will not flow evenly toward the draw-off point, and you could be headed for trouble. At this point, you need to let more liquid into that portion of the pan to re-establish flow toward the draw-off. Maintaining a constant even flow of syrup in the form of low volume draw-offs stabilizes the process. Make all your adjustments in small increments and remember it takes time for that adjustment to affect the process.

Three important factors must be controlled to maintain a constant boil.

  • First, maintain a steady even fire in the firebox.
  • Second, control your foam in the flue pan.
  • Finally, control niter build-up.

In Part 3 of this series, the focus will be on controlling foam and niter build-up in the syrup-making process – come back next week!

Author: Les Ober, Geauga County OSU Extension

All Things Evaporators: Part I

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A Simple Yet Complex Process

Many producers refer to boiling as the art of making maple syrup.  Boiling on a modern evaporator is a process requiring about 45 minutes to move from the inlet at the start to the draw-off at the finish.  Bringing 2% sap through a float at the back of the machine and moving the sap forward  through a series of channels until it reaches 66 Brix at the opposite end may sound quite simple; however, properly boiling syrup is a very complex scientific process based on physics, chemistry and microbiology.

To meet USDA Standards, maple syrup must be at least 66 percent sugar. This is referred to as syrup density which is measured in Brix. Brix is a measurement scale based on the percentage of sugar in a sample. Because Syrup is made up of over 98% Sucrose sugar, we simply define the density of maple syrup as percent sugar. In this case, 66 Brix syrup would be 66 percent sugar. Once we know the percentage of sugar in sap, we can determine the amount of sap that it takes to make a gallon of syrup. To do this we apply a simple formula – the “Jones Rule of 86” – where you take the factor of 86 and divide it by the percent sugar to obtain the number of gallons of sap required to make one gallon of syrup.  For example, 86 divided by 2% sugar content sap equals 43 gallons of sap to produce one gallon of syrup.

You can start to see how chemistry and a little math plays a role in converting sap to syrup. What about physics? When sap is boiling, a gradient is formed causing the heavy syrup to move in front of the lower density sap. If the pan on the evaporator is boiling, then the two will not mix unless you suddenly lower the temperature in one section of the pans. Disrupting the boil results in an intermingling of sap temperatures which causes a drop in boiling intensity. The result is the dreaded big batch and improper syrup density.

Microbiology comes in to play when colonies of microbes begin to increase. Lack of microbial sanitation is the most common reason for the darkening of syrup potentially resulting in an off flavor. Microbial action changes the sucrose to invert sugars (glucose and fructose). As the percentage of invert sugar increases, heat causes syrup color to darken. It is possible to darken the syrup to a level where the color and flavor are severely impacted. If you ignore any or all of the science involved, you could end up with something that you will definitely not want to put on your own table let alone sell to your neighbor.

Managing Your Flue Pan

The flue pan is where all the heavy lifting of the boiling process is done. There are two basic types of modern evaporators, raised flue and drop flue. The level of sap in a pan is controlled by a float box. With a drop flue, you only have one float box controlling the depth of the sap throughout the entire machine. The sap level is maintained at 1.5-2 inches from back to front. Two inches depth is a safe starting point for beginners. Any change you make to the float at the back of the evaporator will be transferred forward to the draw-off point. Thus, all changes should be minimal and incremental. A raised flue evaporator has two floats, one for the back pan or flue pans and one for the front pan or syrup pans. Though you are still running just one evaporator, you can control two separate processes. The double float design allows you to run your depth in the back pan at 1 inch while running the front pan between 1.5-2 inches. The dual control increases evaporator efficiency, more rapidly boils off water, and better controls the draw-off process. The shallower you can run the back pan the more heat you transfer into the sap and the harder the boil. If you run your back pan too deep, the boil slows, and efficiency is reduced.


Raised Flue Evaporator with device to evacuate away steam from boiling process.

Which style of evaporator you prefer is strictly a personal preference. And once you learn your evaporator’s sweet spot, once the depth is set, you can generally leave it alone. All evaporators should have at least one sap level gauge on the flue pan (raised flue evaporators should have a second gauge between the two front pans). A properly calibrated gauge allows you to know the exact sap level no matter if the flue pan is hooded or clouded with steam.


Drop Flue Evaporator with reverse front flow pan.

When running your evaporator, the basic goal is to maintain a boil across the entire rig with the hardest boil occurring in the flue pan. There is an old saying among maple producers, “You haven’t earned your producer’s badge until you have burnt a pan.” Trust me if you have never scorched a pan, or come close to burning one, consider yourself lucky. Usually the most common reason for burning a pan is human error, usually caused by a distraction. When you are running a rig, you are dealing with extreme heat. Stack temperatures can run between 600-1000 degrees F. You are applying that heat to a relatively small skinny volume of liquid (2 inches spread across the surface of the pan) separated by a thin layer of stainless steel. The only thing that keeps that metal from melting is the thin layer of sap on top. If the sap boils out because you forgot to turn on a valve or you ran out of sap, bad things happen very quickly. Uncontrolled high temperatures can go from a scorch to buckling a pan in just a few short minutes. Your season could be over if you cannot find a replacement.

Tracking bubbles in your sap is a good way to monitor your boil. The bubbles in the pan should be moving slowly in one direction toward the draw-off. If the boil decreases and the bubbles move back and forth then an adjustment needs to be made immediately. If you spot trouble the first thing you must do is avoid panic. Move quickly and precisely. This is where knowing what to expect and what to do is vital and that only comes with experience.

Stay tuned for Part II next week!

Author: Les Ober, Geauga County OSU Extension

A Few Thoughts on Finishing Maple Syrup

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Cold weather has set in and that has allowed me to scan the maple chat rooms. Many of the questions that keep popping up are about finishing maple syrup. Is it too thick or too thin? Should I use a thermometer, hydrometer, and/or refractometer? Here are some of my thoughts on the subject.

Most of these questions are coming from backyard producers with a relatively small number of taps. Making syrup on a flat pan or hobby rig is not an easy task. You deal with a lot more “what if’s” than you would on a big evaporator. The process is simple – build a fire under your pan and bring your sap to the boiling point of water. Use a thermometer to monitor the process. That thermometer reading will vary from day to day depending on the barometric pressure. When the temperature goes 2 degrees Fahrenheit above the boiling point of water, add more sap, preferably pre-heated sap. Continue the process until all your sap is in the pan and begins condensing down. At that point, stop boiling, take the liquid into the house to store, and finish the batch. Most hobbyists follow this procedure and it works well. The trouble starts when you have a rig that looks like a big evaporator but does not run like a big evaporator. Many hobby rigs have channels and a heater pan and that is good. Sap should come into the back channel and gradually work its way to the channel on the opposite side near the front. Higher density syrup should move ahead of the lower density syrup. The problem comes in when you have to decide how much sap to let in at any one time. It works okay as long as you can maintain a steady flow into the rig. You need to maintain a depth of 2-3 inches across the entire evaporator. Overflow the hobby rig with liquid, and you will kill the boil. Once this happens, the sap of lesser density intermingles with the heavier density syrup. Big problem! Despite the fact you have channels, you are now no better off than you would be with a flat pan. On commercial evaporators, we have a thing called a float that automatically maintains the level of sap moving across the rig. With a hobby evaporator, you are the float and maintaining the proper level takes time and experience.

A few words on syrup-testing instruments. As stated above, you absolutely must have a thermometer. Two other tools that I recommended are a hydrometer and a refractometer. The hydrometer is necessary and a refractometer is nice if it fits your budget. Others have mentioned the Murphy’s Compensation Cup. I have used one for the last three seasons, developed by Smokey Lake – the Murphy’s Cup is a very useful tool.

I have two ways of measuring density directly off the evaporator. Here is the formula I use. First, I draw a sample into a hydrometer cup once the temperature reaches 7 degrees above the boiling point of water. Remember thermometers need to be calibrated. With your hydrometer cup filled with hot syrup that is above 211 degree Fahrenheit, insert the hydrometer into the cup. When it hits the top red line, you have syrup. I check this several times. Once I have the syrup where I want it, I pour one of the samples into the Murphy Cup. This device has a dial with corresponding numbers to those on a hydrometer. You insert your hydrometer into the cup and let it settle for 3 to 5 minutes. When the reading on the dial and the hydrometer match, you are at the right density. After that, I can fine-tune my auto draw-off for subsequent runs. On the last run, we are hitting between 66.0 and 66.5 Brix with this system. Refractometers are available in digital and analog versions. The digital versions seem to be the most popular. They are very useful to check syrup prior to bottling. Do not use a refractometer at draw-off, a refractometer’s reading is only accurate on temperature-stable and filtered syrup. The only reason for us to have a refractometer in the sugarhouse is to check the sugar content of concentrate coming off your reverse osmosis unit.

Author: Les Ober, Geauga County OSU Extension

Things You Can Do to Ensure the Quality of Your Maple Syrup

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This post is in response to Dr. Michael Farrell’s article on maple syrup quality from the most recent Maple News. First let me say that the article was not only excellent but very timely. The article addresses an issue that all maple syrup producers should consider as another season is upon us. What I hope to do is highlight some of the areas in the production process where syrup quality can be compromised often resulting in off flavors. The University of Vermont and the Vermont Ministry of Agriculture has provided an excellent tool for identifying the sources of off flavors in maple.

After producing maple syrup for over 40 years and teaching seminars on maple syrup production for close to 20, I have made or personally witnessed most of the common mistakes that lead to off flavors and poor syrup quality. In this article I will go over some, but certainly not all, of the factors that lead to poor syrup quality. The good news is that most of the factors can be controlled by producers with best practices, in turn meaning you control the quality of your syrup. The Map of Maple Off Flavors (linked above) identifies 5 primary areas where off flavors occur: Mother Nature, defoamer, processing, chemicals and others. I want to address each area in order of how they would occur from start of season to finish.

When you start out the season, you need to be aware of several problem areas that can lead to off flavors. Most problems arise from the previous season’s equipment maintenance and show their ugly faces as the new season kicks off. When producers ask how they should clean equipment, my response is with a lot of water and elbow grease – and my answer is the same from large-scale producers all the way down to backyard hobbyists. Anytime chemicals are used to clean equipment, residuals left behind can compromise flavor. If you use chemicals on your pans to clean them at the end of the season, you need to thoroughly scrub away any chemical residue. If you use a tubing cleaner, make sure it is flushed entirely from the system. If you store filters make sure there is no mold on those filters when you dig them out of storage. (And never use detergents to scrub away mold on filters, THROW THEM AWAY!) The list could go on. A final guideline for this area is to always store your chemicals in a secure place away from your syrup processing so as to avoid unintended contamination of your final product. Most of the above is common sense but they need to be mentioned.

Probably the biggest culprit for off flavors comes during the processing stage. This is where the majority of mistakes are made that result in off flavors. When we grade syrup, we look at 4 primary areas density, color, clarity, and flavor. Even though each is judged separately they are actually all interrelated. Syrup must be 66 Brix to meet USDA standards and if it is below 66 Brix it can ferment and cause an off flavor. Syrup above 67 Brix normally does not have an off flavor but the higher density can cause crystallization in the bottom of each container resulting in lost revenue to the producer. As syrup moves across the front pan, density and color changes rapidly. Density changing with the rapid removal of water that increases sugar concentration, and color as heat changes the sugar molecules. Anything that interferes with flow of sap through the evaporator can cause the syrup to get darker and possibly cause an off flavor. Many feel that density is the most critical part of the process and at times reaching the proper density can be very difficult. Improper density management can lead to two off flavors that are very common in syrup – fermented and scorched. And these off flavors are often accompanied by undesirable colors as well.

We use three tools to measure density, the hydrometer, the thermometer and the refractometer. All sugarmakers use a hydrometer. Hydrometers should be inspected or checked for possible problems and replaced if suspect. Often the paper with the scale printed on it can slip resulting in the wrong Brix reading. Hydrometers can become coated with film resulting in inaccurate readings. A good hydrometer will give you an accurate reading only if it is used at the right temperature. Temperatures below that require consulting a chart to convert to the right Brix reading based on the specific temperature. Maple syrup boils at 7 degrees Fahrenheit above the boiling point of water or 219 degrees, and many producers use a thermometer to determine the draw off point. The only problem is that the 219 reading is only accurate if the barometer is at 29.9 Hg barometric pressure. Therefore, a thermometer needs to be recalibrated every time the barometric pressure rise or falls. Having an accurate syrup temperature is especially vital when it comes to setting an automatic draw off.

The final tool is what many consider the grand judge and jury of maple syrup density – the refractometer. For a refractometer to work properly, syrup must be finished and stable in temperature. This was pointed out the other day in a conversation with Robert Crooks of Marcland Instruments. For a refractometer to work properly, it has to be able to refract light coming through the sample and that can only be done accurately if the sample in the instrument is a clear finished sample. Taking a sample of cloudy unfiltered syrup will lead to an inaccurate reading. The temperature of the syrup also affects light refraction. Even though refractometers are built to automatically compensate for temperature, temperature must be stable. If you leave freshly drawn off syrup set in a container, it will continue to evaporate water until it cools down. Think of what happens to a pot roast when you pull it from the oven, it continues to cook beyond the temperature when you pulled it from the oven. This is why it is best practice to cover containers of hot unfiltered syrup in order to stop moisture loss. If you use a refractometer to set the draw off, run a sample of syrup through your filter and allow the sample to sit for 15 minutes before taking your refractometer reading. This will give you the most accurate reading from your refractometer.

If you use a conventional auto draw-off, be aware that it takes time to complete the draw off process. This means that syrup will be drawn off over a range of temperatures. Therefore set the draw off to actuate slightly below the desired temperature and it will finish slightly above. Using a hydrometer is the best way to set your draw off. However, make sure you are reading the hydrometer at the recommended syrup temperature. You can use a refractometer but remember it must be used on a finished, stable-temperature product, and this process may take more time than you have to make a correction on the draw-off.

As sap moves across the evaporator, a temperature gradient sets up. Ninety percent of the water is removed by the time the sap reaches the middle of the front pan, so syrup needs to move from the middle of the syrup pan to the outlet relatively fast to avoid darker and denser syrup than desired. A common mistake is to allow the pans to cool during the firing process. Anytime you cool off the pans, the temperature of the sap drops and this causes the boiling temperature to drop resulting in the sap on one side of the gradient to mix with sap on the other. Keeping constant and stable heat levels on the front pan is must and particularly crucial for wood-fired evaporators.

Another problem is foam control. Excessive foam in the back pan can cause problems with your float and may interfere with your ability to control the level of the sap in the evaporator. If this happens you will need to use a defoamer to control the problem. When using defoamer, the only place the defoamer should be added is at the point where sap enters the rear pan, and occasionally a couple of drops if needed at the draw-off if foam builds up as you are drawing off. This should be done at regular intervals placing the prescribed number of drops (2 drops per foot of width) where the sap enters the evaporator. Never spray defoamer across the front pan to control foam. Using defoamer in this manner will impede the boil and break down the temperature gradient. This can lead to the dreaded big batch.  If the front pan is foaming excessively, then the foam is not being properly controlled in the back pan, correct the problem back there. Use only small amounts of defoamer, excessive use can result in an off flavor. Organic producers must use safflower or canola oils which are very poor defoamers. And be careful with organic products as well because an excessive amount can produce off flavors.

Another potential problem (there are a lot of them, right?!) is niter build-up which can lead to scorching in your evaporator. Any niter build-ups will insulate the bottom of the pan from the syrup creating a potential hot spot which can eventually result in a scorched spot on the pan. You must keep liquid in contact with the pan at all times. Always keep your pans as niter free as possible by rotating sides or using a clean set of pans between batches. Using a good syrup filtering system to remove niter is vital if you want to produce syrup that meets the highest clarity standards. You should be able to read newspaper print through a sample bottle of syrup that has been properly filtered. Cloudy syrup with a lot of niter can produce an off flavor. Remember every time you heat your syrup to a boil, more niter will precipitate out and needs to be re-filtered. That is why you do not want to bring your syrup to a full boil when canning. 185 degrees Fahrenheit is the required temperature for canning.

As maple producers, we fight the growth of bacteria through our entire system. When bacterial colonies multiply in sap, they convert Sucrose sugar molecules to Glucose and other invert sugar molecules. This increase in invert sugar, when exposed to heat, will lead to a darker finished product. This is most prevalent at the end of the season when the bacterial content of sap is at its highest. Bacteria can affect the entire process of making syrup from the taphole to canning. Because sap has sugar content, it is a perfect media for bacterial growth. It goes without saying you can never be too clean when it comes to making syrup. Sap needs to be collected in clean equipment, it needs to be kept cool, and it must be processed quickly. If you start with a properly sanitized system at season’s beginning, you will have far fewer issues at season’s end – though issues may still crop up. Maple producers need to know when to end the season. Producing syrup late in the season when the trees are near budding and the sap is out of peak condition has little value to you and even less to the industry’s customers.

As you can see, there are many factors that a sugarmaker must consider in order to maintain the highest standards of product quality. From equipment sanitation to efficiency throughout processing, paying attention to details is critical and is what separates the best producers from the rest of the pack. Making the highest quality product possible should be your goal. Your reputation as a maple producer depends on it.

Author: Les Ober, Geauga County OSU Extension