All Things Evaporators: Part III

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