Controlling Your Heat and Boiler Temperature vs. Vaporization

Posted by Jeff on 13th July 2015

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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, but here is the more in-depth explanation as to why you need to be able to control 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

Ethanol Phase Diagram

Ethanol Phase Diagram

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!

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7 thoughts on “Controlling Your Heat and Boiler Temperature vs. Vaporization

  1. thomas edwin

    I have a 15.5 gallon beer keg with a 3 inch x 6 foot packed copper column and dephlegmator. I currently have a turkey fryer converted over to natural gas with a 18 jet wok burner. I light the burner under my keg set it at a nice blue flame and let it go, I don’t ajust it any during the run. When it reaches vapor temp it runs at about 180 degrees F and then slowly rises, and when it reaches 200 degrees F I shut it down this first run makes 180 proof the second run starts out at real close to 173 F and slowly rises to 200 F this second run makes about 193 proof, out of 30 gallons of mash I get about 4 & 1/2 to 5 gallons of almost pure ethanol, at no time do I tamper with the flame ajustment. I have my eye on a 6000 watt heating element controller and thought about using a 5500 watt heating element,so I’m guessing for the first electric run I would just crank up the controller slowly until I get an output from the condenser and just let it run until the column vapor reaches 200 degrees F the same as I did with the flame and I think I should get the same results. I’m moving to a apartment so the switch to electric heating is inevitable. Do you think a 5500 watt element is enough for 15 gallons? and how long do you think it will take to come to a boil for distilling?

    1. Jeff Post author

      Typically, a 5500W element will bring our 13 gallon boiler to a boil in about an hour. However, this may vary a little depending upon the starting temperature of your mash.

  2. thomas edwin

    The way my rectifier column works I can play with the temp a little bit as long as I keep the column vapor temp over 173 F and below 200 I get mostly alcohol coming over into the 7 tube shotgun condenser. When I start my first run I get a strong constant output and as the wash content becomes more and more water I just get less and less of a stream coming out of my condenser and when the vapor temp gets near 200 degrees F the output goes down to almost nothing when it does reach 200 F I shut it down because I know it’s mostly water coming over. I know this because I did the one bottle at a time test where I filled 1/5 bottles one at a time and filled a hydrometer test tube at the start of each bottle and at 200 degrees F its down to about 35 or 40 % ABV at that point I stop collecting, in this way I remove all the tails.

  3. charles

    i run a 15 gl beer keg still with copper reflux top mabe u can help they say run it at 172 dgs but it dont boil at that temp it will at 194 dgs i get a nice slow flow & a good tasting run is it safe to run it at 194 dgs thanks for any help & any tips

  4. tj

    My vapors don’t seem to be condensing. I have vapor and stems coming out ware I should be collecting, and very little actual liquid. I can’t seem to get everything running smooth,

  5. DHS

    I ferment my mash in a 60 liter kettle, which i leave on the stove for about 2 weeks. I siphon off about 45 liters of usable wash including the last of the grain liquid I extract using a fruit press. I use a 20 liter still heated by a 1800 watt induction heater. I set the heat at 320° F until the vapor temp hits 90°, then reduce the temp to 210°. I don’t do any cuts until the secondary distillation. I run 3 batches, then dilute the shine to 38% and start my srcondary. I note temperature on each mason jar, along with proof. Foreshots come off between 130 and 164. About 250ml is all I toss. I then get about 7 liters in ten mason jars. The heads result from vapor temps from 164-170, with proofs running from 156 to 150. The hearts start about 170 and I get about 3.0 liters of 144 proof average. The last 2.5 liters are tails, which I run again with the heads at my next run. This was the result of my last run, which included me losing a gallon of my primary run to a smashed carboy! This is all a long way of saying that no adjustment of heat is ever necessary, as long as you can keep it constant. The alcohol in solution will control your actual wash temperature. I stop everything when my vapor hits 190.


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