In this episode, we are talking to John McKee of Headframe Spirits. We talk about the history of Mining in Butte, America and then get into continuous still design and ways to make your wash production have a higher yield. Later, we’ve got some bonus information on continuous stills and theoretical plates.
There are two main types of distillation: Continuous and Batch. Continuous distillation allows for a more thermally efficient process where the wash is only heated a single time and less heat is wasted dumping the stillage. Continuous distillation also takes less time in filling/emptying the still since this is done during distillation. Yields are also higher in Continuous distillation since less ethanol is left in dumped stillage.
Generally, there are two types of stills: Column and Pot styles. Column stills create more rectification by allowing the vapor to condense and redistill more times (in the vast majority of cases) before making it to the condenser. Each stage of condensing helps separate the different elements. In a Pot still (or packed column) there are theoretical plates – where the liquid condenses and then redistills. The number of theoretical plates can be calculated and changed by things like exterior cooling, condensing/expansion, or pulling a vacuum. A combination of the two styles can be combined to create a third style: the hybrid still. The hybrid allows more flavor to be passed through than a traditional column still while creating more reflux than a traditional pot still and typically has 3-5 actual plates.
When taking developed products from a Column to a Pot Still the flavor profile will change due to the greater pass-through. If developing a product on a Pot Still – the number of theoretical plates should be used to determine the quantity of plates in the Column Still to replicate the Pot’s flavor. (I find it is a good idea to add one or two additional plates to the column height than calculated; since it is easier to take plates away than to add them in later.)
Wikipedia has a nice write up on Theoretical plates: here.
If you would like to learn more or if you’d like to learn way, way, way too much, I like Perry’s Chemical Engineers’ Handbook. Here is a link to it on Amazon – but, I’d check your local library.
The most common methods to heat a still are: direct heat and steam. Direct heat involves putting the heat source directly on the still either with immersion electric heaters or building a fire under the still. Direct heat can be done safely – but, it does require additional engineering controls to ensure that if there were a problem, ethanol vapor over the LFL would never contact or connect to a heat source (your direct fire) and start a deflagration of the fuel/air mixture (read: destructive fire with firemen and fire trucks, a closed facility, and big insurance claim). Indirect heat in a distillery – is easily achieved by a low pressure steam boiler sealed in another room from the still. The heated steam is piped to the still to provide the energy used for heating. The most thermally efficient method for doing this is direct steam injection. The problem with direct steam injection is it decreases your ethanol yield; 500 gallons at 7.893% alcohol by weight you’ll get about 42% by weight vapor with 500 pounds of steam per hour during heat up and 100 pounds of steam per hour during distillation (15 psi) assuming you stop stripping at 211°F you will leave 1% ABW in the still but will have added ~132 gallons of water so that means your pot volume will remain about 500 gallons instead of decreasing to ~350 and that 1% will represent about 2.5 gallons of 60% alcohol that will be left behind compared to a steam jacket.
Here is an Ethanol/Water equilibrium table with the redlines showing the theoretical plates needed to move from 10% ABV to 93% ABV. Keep in mind that after the first bit of ethanol has evaporated the liquid in the pot is at a lower ABV and the entry point to the table shifts to the left so a 5 plate column won’t turn 10% wash into 93% hearts. This chart is for pure ethanol/water mixtures. Any impurities like flavor compounds – or, even different pressures – will change the numbers, and the results you see if trying to match this with your still. This table also shows why 3 and 4 plate hybrids work so well.
Here is a zoom in on the wash section of the chart this time in % ABW and you can see the difference in ethanol vapor decreases significantly with even minor changes to wash ABW. Lines are equivalent to 10%, 8% & 1% ABV.
120-gallon batch size 10% ABV with 1% ABV left in pot
A) Whiskey
B) Vodka
C) Need 20,000 4.5L-cases
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