Monthly Archives: March 2014

The Finishing Pan; Where The Art of Making Maple Syrup Meets the Science of Making Maple Syrup

 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.

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Managing Your Flue Pan

Les Ober OSU Extension Geauga County

                In the last column I discussed the overall basics of running a modern evaporator. You will notice that there is a lot left out of that very basic discussion. Let’s take a more in-depth look starting with where the sap enters the evaporator at the flue pan float. If you have your float set properly the level of sap in the back pan can vary between 1 and 2 inches depending on the style of evaporator you are running. As mentioned in the last article if you have a drop flue then you set the level of sap for the entire rig with the back float. A raised flue evaporator has two floats and this allows you to set the front and the back pan independently. It also allows you to run the back pan a little shallower than you would with a drop flue. The shallower you can run the more heat you transfer in to the sap and the harder the boil. If you run your back pan too deep then the boil slows down. Every evaporator has a sweet spot and once you get it set, you usually leave it alone. Remember if you make a change at the float, a reaction to that change will take a significant amount of time. All changes should be minimal, as large changes will alter how the rig is running.   Another good idea is to have calibrated site gauge in a position so you know what the level is at all times. By calibrated I mean make sure that the level you are reading on the gauge is the same as the level in the pans. This is should be the level of sap above the flues. Check this before you start your rig. When running a pan a little on the lean and mean side it is a good idea to set up some kind of an alarm system just in case the flow of sap is interrupted and the pan level drops to below the critical level. All of these suggestions just might save a pan from burning up.

               The proper use of deformer in the back pan is critical. According to Leader Evaporator Company if the defoamer is used on a regular basis in the back pan you will very seldom need to use in the front pan. In fact except for the occasional use at the point of draw-off, defoamer should not be used in the front pan.  There are several ways to accomplish this. Several Years back Bradley Gillilan of the Leader Evaporator Company authored a book entitled Boiling 101 Tip and Tricks to Make Better Syrup. This is a must read for anyone who is running an evaporator. I think the book is still available through the company. One of the discussions is the use of defoamer and how it varies from one style rig to another.  Defoamer is needed because one of the inherent characteristics of sap is that if foams excessively when boiling. When foaming occurs the boiling rate slows down and the flow can even be interrupted. It is necessary to add a small amount defoaming agent to prevent this from happening. You add just enough to stop the foaming but not enough to kill the boil. Too much defoamer can also alter the flavor to the syrup. Most new evaporators use defoamer cup in the back corners of the flue pan. They are shallow cups suspended at height that will stop the foam level at the height of the cup. This continuously controls the foaming level in the back pan. Other producers prefer adding a drop or two to the back pan every time they fire up. Either way regularly managing the foam in the back pan will usually mange the foam throughout the entire rig. It will also promote and even flow and smaller batches.    

                Why would I want to spend $2000.00 on a pre-heater? After all the best I can hope to gain from this accessory is 10 to 15 % increase in efficiency. Would it not be better spent on an RO or a steam-a-way or piggy-back? The answer to the last part of the question is strictly economics. Both, a steam-a-way or piggyback, are very expensive additions to an evaporator. My personal thoughts are that t it is much better to put the money into enhancing your RO. The advantage you get from increasing your RO capacity will outweigh the money spent on a steam enhancement device. However, that being said I have seen phenomenal results when an RO and a Stem-A-Way are used together. Producers have reached levels in excess of 1000 gallons of sap an hour being processed with a single 3X12 rig. Again it is all about economics.

               The pre-heater is another matter. The use of a preheater is not so much to gain capacity as it is to gain efficiency of sap movement. The issue here is what happens when you put cold sap directly into an evaporator. When this is done you literally kill the boil at that point of entry. On very large evaporators with long flue pans this is not as critical but on small evaporators killing any portion of the boil on the flue pan will decrease you capacity. On a 4 X 10heater pan divided in 4 sections you have 40 square feet of surface above the flues. If you kill the boil on just under half of the section where the sap enters ( 1 foot by 4 foot)  you will only lose 10 % of your capacity in the pan. Now if you lose the boil on the same area in a 3 X 5 heater pan you would lose close to 25 % of you boil. Considering that 75 to 85% of the liquid is evaporated in the flue pan that is a significant loses.   A preheater designed to bring the temperature up to 190 degrees F is a valuable addition to your small evaporator. The use of pre-heaters went by the wayside when the use of Steam-a-Ways and RO increased. In old days you hardly ever saw a rig without some way of pre -heating the sap. Today many dealers recommend the use of a pre-heater on smaller rigs. A word of caution when using a preheater! Watch the flow of the preheated sap going through the float, If the sap starts to boil in the pre-heater it can vapor lock and shut of the flow. You always need to properly vent a preheater according to dealer recommendations.

               When you put it all together the boil in the back pan should be vigorous and uniform across the entire pan. You should see the bubbles moving in the direction of the flow. If the boil decreases and the bubbles move back a forth then an adjustment needs to be made. Efficiency in the back pan  will largely determine the capacity of your evaporator.




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