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.