Les Ober Geauga County OSU Extension
The old timers called it an art, modern maple producers call it a science and in reality it is a little of both. What happens in the finishing pan can determine the success or the failure of a season. It is here that all of the standards that we base quality maple syrup on come together. Here 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 six sense of knowing when everything is moving toward the perfect draw-off. The result is golden amber maple syrup with the perfect maple flavor.
There are several types of finishing pans on the market today. The reason for the difference is to manage niter or sugar sand. Niter is the mineral content in the sap that precipitates out in the boiling process. To manage niter, most front pans are designed to either change to a side or to pan with a lower deposit of niter. The reverse flow allows the operator to switch sides when niter builds. A variation on design is the one-sided draw-off, reverse flow where a series of valves are used to redirect the flow of sap from one side to the other. An example of this would be the Leader Revolution. The other style is the cross flow, where there are multiple front pans connected by stainless tubing. In this configuration the pan closest to the draw off point is rotated with a clean pan. The best policy is start with a clean pan every day and change during the day when needed. 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. The amount of niter present in sap varies from season to season and from woods to woods. If improperly controlled the result often be a scorched pan.
Once the sap or in this case concentrated sap reaches the front pan, or the finishing pan, it is approximately 19% sugar. This is sap that has not been run through an RO. It has been concentrated by boiling. RO Concentrate will enter the pan at a higher concentration. As the concentrated sap is crossing over into the front pan it should be reaching 213 degrees at 29.9 barometric pressures. It is also at this temperature that the concentrated sap is not only becoming denser but is starting to change color. As the density increases, the sugars react with the heat to form the amber color we associate with pure maple syrup. It is also at this time when the bacteria in the sap can interact with the heat and the sugars and darken the syrup. All of this happens in the finishing pan and over a relatively short amount of time. This reaction can occur quickly and if the operator is not paying attention he can actually burn or caramelize the syrup, darkening the color. He will also increase the density past 66 brix. The result is thick heavy syrup and possible loss of profit.
To make sure we pull the syrup off at the right density, we can use a variety of instruments. The most common and least expensive are the thermometer and the hydrometer. Most evaporators come with a thermometer that is placed at the point of draw-off. Water boils at 212.1 degrees Fahrenheit at sea level and a barometric pressure of 29.9 in. of mercury. Because syrup in rarely produced in a location at sea level and the barometer is seldom at 29.9 we must make some adjustments. We must boil water near the evaporator and reset the thermometer that is used to make syrup. This process of adjusting to match the barometric pressure must be done daily and whenever the barometer changes due to weather front movement. This can occur quite often during an average sugar season. This is why most producers would rather use a hydrometer for the final test and use the thermometer to give them an approximation of when to draw-off.
The hydrometer is the judge and the jury. There are two lines on a hydrometer the top line is for hot syrup the bottom line for cold. Use the top line. Always use a hydrometer cup full of syrup that is at least 211 degrees F. Bring the instrument up to eye level or set it on a stable object close to eye level for the most accurate reading. Producers need to test their hydrometer annually against a calibrated refractometer. The hydrometer gets jarred around and the paper containing the scale can move or it can get dirty and give a false reading. If the reading is inaccurate replace it. Another tool is the refractometer. The new ones are digital, very accurate and are temperature compensating. However, the cost may prevent many from using them.
The automatic draw-off is a great tool for any producer in any size operation. It will make drawing off syrup a lot easier, especially when boiling RO Concentrated sap. It is nothing more than a digital thermometer hooked to a valve that draws the syrup off at a very precise temperature. Everything I said about the syrup thermometer applies to the auto-draw-off. Most producers set there draw-offs with a hydrometer. During the sequence of opening and closing the auto draw-off is actually working within a range of temperatures. The thing to remember is that the draw-off will open at very precise temperature but if the flow is slowed by foam or a valve coming into the draw-off is restricted the temperature will rise above the desired level resulting in denser syrup. All auto draw-offs should be installed with a valve between the pan the draw-off. This allows the producer to adjust the flow of sap coming off the pan. Open the pan valve so a steady stream flows through the auto draw-off. Try to avoid a heavy stream that will result in the large batch. The draw-off should close and the temperature on the readout should drop 4 to 6 degrees and then quickly rise coming back to the desired temperature. The result is a series of small batches coming off in a relatively short amount of time. The producer needs to check the final product in the bucket or tank when the auto valve closes and adjust the draw-off accordingly. It is very easy to get a denser product than desired. The auto draw-off monitored often during the day. It is not a set and forget instrument. Today there are newer auto draw-off that compensate for barometric pressure but again the cost may be prohibitive for the small producer.
Another area to consider during the finishing process is foam control. You only control foam in the front pans at the point of draw-off and only if the flow out of the draw off point is being held up by the foam. If this happens one drop will reduce the foam to the point where the bubbles will decrease and flow will increase. Avoid using defoamer anywhere else as it causes the gradient to break down and the syrup densities to intermingle. If you are foaming over in the front pan it is usually because the foam is not properly controlled in the flue pan. Occasionally it may be necessary to knock this foam down but try to avoid this action if you can. If the foam is properly controlled in the flue pan there should be minimal problems in the front pan. The only exception would be coming into the first draw-off after a layoff. All types of sap will behave differently during the initial draw-off. Watch for increased bubbles and denser steam, this is a sign that you are making syrup across the front pan. In this case do not panic, if you can slow your boil down and stabilize the evaporator as quickly as possible. The result is usually one big batch of syrup followed by reduced boiling temperature. The next batch should be normal if not look for the problem.