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, refractometer or all of the above. Here are some of my thoughts on the subject.
Most of the 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 I do 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 above the BP of water, add more sap. Preferably preheated sap. Continue the process until all your sap is in the pan and it starts to condense down. At that point, stop boiling, take the liquid into the house to stove and finish the batch. Most hobbyist I know follow this procedure and it works well. 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 lessor density syrup. The problem comes in when you have to decide how much sap to let in at any one time. It works ok as long as you can maintain a steady flow into the rig. You need to maintain a depth of 2 to 3 inches across the entire evaporator. Overflow the hobby rig with liquid and you will kill the boil. Once this happens, the sap of lessor 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, maintaining the proper level takes time and experience.
A few word on instruments to test your syrup. As stated above, you need a thermometer. Two other tools that I recommended are a Hydrometer and a Refractometer. The Hydrometer is necessary and the Refractometer is nice if it fits your budget. Others have mentioned the Murphy Cup. I have used one for the last three seasons. Developed by Smokey Lake this 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 BP of H2O. Remember thermometers need to be calibrated. With you cup filled with hot syrup that is above 211 degree F 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 set 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. On the last run, we were hitting between 66.0 and 66.5 brix with this system. Refractometers come 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; it 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 the RO.