When talking to folks about their runs, there always seems to be a lot of confusion around why you need a heat controller and how you can use it to control your boil temperature. Simply put, you can’t use it for boiler temperature control, but here is the more in-depth explanation as to why you need to be able to manage your heat.
Since you are reading this I am going to assume you already have a pretty solid understanding of basic distillation, and if not, you should go touch up on that since a lot of this probably won’t make any sense!
Boiler Temperature vs. Speed of Vaporization
So, let’s start from the beginning. The whole idea is to boil your mash to take advantage of the fact that alcohol boils at a lower temperature than water (and a lot of other compounds that you don’t want in your final distillate), resulting in something that has a higher ABV. The alcohol distillation temperature that the mash will boil at depends entirely upon the ABV of the mash that is boiling, and based on this ABV will boil somewhere between the boiling point of ethanol (173 F) and water (212F), unless you are 9000 ft above sea level like us. The higher your washes ABV is, the closer your temperature will be to 173. And the lower your ABV is, the closer your temperature will be to 212. To further complicate things, as you start to boil the ethanol out of your wash, the ABV of the wash will decrease, so the temperature that it boils at will also change. To see this illustrated, see the chart to the right, and maybe even print it out for future reference!
Again, this is very important to repeat: the ABV is the only thing that will affect the temperature that your wash is boiling at (which should be the same as the vapors in the head of your boiler). Turning up the heat to your boiler will not increase this temperature (unless your mash hasn’t started boiling yet). What turning up the heat will do is increase the rate at which the wash is being vaporized (making a liquid change its phase into a gas takes energy).
If you don’t believe me, think about the way boiling a pot of water on the stove works. Water boils at 212. Once it reaches that temperature, it starts boiling, but it does not go above 212. Turning up the heat makes it boil faster (increased rate of vaporization), turning the heat down makes it boil slower. Make sense?
This leads me to why you need to be able to control your heat input; you need to be able to control the rate at which the vapors are traveling up your column or into your still head. The reasoning behind this is slightly different for a pot still vs. a reflux still.
Why you need to control the rate of vaporization
Controlling the rate of vaporization is important for a pot still so that you do not end up pumping vapors through so quickly that the condenser cannot condense it all back to a liquid. When this happens, you end up with vapor blowing out of the end of your still, which hopefully you know by now is very bad! The only exception to not needing to control the rate of the boil is a heat source that physically cannot put out too much heat for your condenser. For example, our 1500W heating elements can be used without any controller, since our condensers are capable of condensing all of the vapors that a 1500W element will generate (as long as your water is cold enough).
Controlling the rate of vaporization is important for a reflux still so that you can get the right balance of vapors traveling up the still vs. reflux traveling back down (we go over that in this video on running a reflux tower). If you plug a 4500W or 5500W heating element into a dual-purpose reflux still, a couple things (among others) would be likely to happen. First, you would run into the same problem as the pot still, the condenser would not be able to handle all the vapor and it would blow out the end of your still. Second, the vapor would be traveling up the still tower so quickly that it would basically “blow” the vapor up the column. When there is no reflux in the column you don’t get the vapor exchange in all the packing of your column and usually the “blown” vapor will pool on top of your packing until it reaches the lyne arm (at which point the clear distillate will surge out every once in a while). So, long story short, you need to be able to adjust the heat down to a level that will work with your still setup.
Ways to control your heat source
First off, if you haven’t already, see our video about the pros and cons of electric vs. gas heat sources.
Most beginners start with a propane burner setup because it is cheaper, and that is just fine. However, the major problem we find with a lot of the propane burners is that they have trouble going low enough to get a slow, steady trickle of distillate out of your column. They have a built in venturi to help suck in fresh air for combustion, but when you turn the still down this low that ceases to function properly and the flame will burn yellow instead of blue (and leave all kinds of soot on the bottom of your boiler) due to the lack of oxygen.
When it comes to electric heat controllers, there are several different control methods out there. The first to cover are thermostat controllers since we most often see these misused. Thermostats are basically just temperature controlled relays that are 100% on if they are below the set temperature or 100% off if they are above the set temperature. As we mentioned before, the ABV in the wash controls the temperature of the boiling wash, not your heat source. So, this simply will not work to try and control your heat output. Even if you manage to tune it to the exact temperature that the wash will boil at, it will cycle on and off, causing surges of distillate which will wreak havoc on the way a reflux still operates. Plus, as the ethanol gets boiled off, the temperature needed to cause the wash to boil will rise, your heat source will stay 100% off, and the still will stop distilling anything. The main thing that thermostat controllers are good for is getting the still to an almost-boiling and holding it there until you return to do the run or shutting the still off once you get to a higher temperature that should mean you are into your tails.
PID controllers are basically glorified programmable thermostats. As is the case with thermostat controls, they are not ideal. Some do have options to modulate heat by cycling on and off more frequently, however, this also cycles your solid state relay (SSR) on and off much more frequently putting additional stress on it. But, on the plus side, they are programmable.
The last controller type that I want to cover are phase-angle control SSRs. These relays are quite complicated, but I’ll give an explanation a try. They work by only allowing a certain portion of the electricity’s wavelength through based upon the resistance provided by the potentiometer. Since we have 60 Hz power, that is effectively cycling the heating element on and off 60 times per second without actually firing the SSR on and off 60 times per second. This gives you a much smoother flow of energy into your boiler, which then boils your wash steadily. It is important to note, however, that as you boil the ethanol out of your wash, it takes more energy to produce the same column of vapor (since the water content is increased and water takes more energy to vaporize than ethanol). So, you will still need to turn your heat source up every once in a while throughout the course of the run.
So, I apologize, that was a lot to throw at you at once, but hopefully it helps clear some things up. If you have any other questions at all, please be sure to let us know in the comments below!