Hopefully this is a question you are asking because of a bumper crop! But even in any year, if you have not sold all the year’s maple syrup and have some left in the sugarhouse or in a tool shed or in the corner of your garage, then you need to watch the inside temperatures of those buildings. In outdoor non-insulated structures, temperatures can elevate quickly and spoilage can occur. You may have thought that you covered your bases by packing syrup hot in a sealed container. But maybe not!
Let’s look closer at how syrup is packed and stored. Most syrup is stored in stainless steel barrels that were packed in February and March. The syrup went in to the barrels hot and each barrel sealed. Inside a thirty gallon drum there will always be a little room for air no matter how carefully you pack. The drums then cool to and fluctuate with the ambient temperature of the time of the year and soon the syrup inside takes on the same temperature. Steel transfers heat and cold well, but 30 gallons of syrup is a lot of volume and will remain cold for a long period of time due to its viscosity and mass. However, when outside temperatures warm to 80 degrees and above and stays hot, the steel on the outside of the drum heats up quickly often forming a layer of condensation between the warm steel on the outside and the cool syrup on the inside. When this moisture gets into the air space inside the barrel molds can form. This is the same thing that happens to jugs when they are not heated to 185 degrees Fahrenheit, and if the product is not above 66 Brix, syrup can even ferment.
The best solution for keeping your syrup in tip-top condition is to build a cool room. You notice I did not say cold. A walk in cooler would be the best case scenario but most producers cannot afford such a luxury. Take a small space big enough to hold several drums of syrup. This could be a closet or a small room inside a building. Insulate the room and install a window air conditioning unit through the wall. When temperatures go over 80 degrees F for any length of time, fire up the air conditioner and brings the room to just below 70. At that temperature, the syrup will stay relatively cool in the barrels and always trends towards being colder than the outside temperature. This strategy should get you and your syrup through the hot months, then once the daytime temperatures cool off into early fall, you are out of the woods!