Distilling Craft: Ep 002

Yeastie Boys with Sean Smiley

In this episode, we are talking about yeast. Later in the podcast, I bring in Sean Smiley out of State 38 Distilling in Golden, Colorado and we talk about developing disruptive products.

Most spirits are fermented with Saccharomyces Cerevisiae but there are some other yeast strains that are capable of forms of sugar to ethanol. Kluyveromyces Marxianus or most Lactobacillus types are those other yeasts that convert lactose preferentially. K. Marxianus is mainly used in industrial fermentations particularly looking at fuel ethanol production while Lactobacillus is mainly used in beverage production. The most common alcoholic drink made from fermented Lactose is Kefir and then once distilled it turns into Arkhi which is basically a double distilled mare’s milk vodka.

Saccharomyces Cerevisiae is the general yeast species that makes up most distilling yeast and ale brewing yeast. It is a top fermenting yeast that made it easy for some yeast cells to be captured in the foam head and repitched for generations. Before the mid-1800s most fermentations were completed with wild yeast that happened to live in the area of the brewery and where these wild yeasts worked well with the local fermentation they were repitched from one batch to the next or would wildly inoculate the fermentations repeatedly. Louis Pasteur developed ways to culture pure strains of yeast which allowed these wild strains to be isolated and then passed from batches with a higher success rate. Locations that had good yeast were then incorporated into the yeast program for the modern yeast companies so when you purchase “rum yeast” it was originally a yeast that was wild at a rum distillery and then was isolated and passed down through generations.

Initially, bakers collected yeast from brewers for use in their bread. Over time these strains have not been as specialized as beer yeast or even distiller’s yeasts. Typically, there are two types of baker’s yeast available with the distinction being how high of a sugar content the dough has. If you are looking for a yeast that has an older more original flavor profile it is possible to reverse the process and go “collect” it from the bakers. Beware that Baker’s yeast will put off strong Sulphur flavors when stressed and has lower alcohol tolerances than many more specialized yeasts. It also can impart banana flavors. The Sulphur problem with baker’s yeast can be overcome by having enough copper in the vapor path of the distillate.

The conditions that Cerevisiae require are typically higher than other yeast strains. Pitch temperatures are typically in the 60-90° F range though people do push higher then that when trying to get the yeast stressed to encourage particular flavor profiles. The initial gravity of the fermentation needs to be in a particular range of each yeast strain since too much sugar will cause the environment to become toxic to the yeast as the convert it to ethanol and sugar above that point will be “wasted” (typically this range is about 8-12% ABV). On the other hand, in order to minimize the amount of time spent fermenting the initial gravity should be as high as possible to create the desired flavor profile, again sometimes stress is good, while letting the yeast ferment it completely so that the ethanol yield per pound of sugar is as high as possible to maximize the return on the dollars spent on the sugar. The other ethanol yield to look at is the gallon of ethanol produced per day if fermentations are kept colder – it is possible to slow them down and allow the yeast to produce a higher %ABV but if it takes an extra day to go from 12% ABV to 13% ABV then on a 500 gallon fermentation 120 proof gallons would have been created on a 3 day fermentation while 130 would have been created on a 4 day (numbers made up for visualization purposes) so you went from making 40 proof gallons per day to 32.5 proof gallons per day. If you have spare time it could be a good way to maximize production but most of the time it will be better to cut short a fermentation rather than waiting for the final bit of ethanol.

The other downside of higher initial gravity is that it creates more pressure on cell walls and makes the yeast less effective this effect is more pronounced in tall skinny fermenters. For instance, a fermenter that is 10’ tall and 1’ in diameter with a 1.1 sg (13% ABV potential) would cause 4.76 psi of pressure on a yeast cell at the bottom. If instead, that fermenter was half as tall (5’) but 1.4’ in diameter the yeast would experience half as much pressure (2.38 psi) while the fermenter would hold the same volume. In general, it has been found that a 3:1 ratio of height to diameter (4.5’ tall x 1.5’ diameter in this case) is most effective for spacing savings and minimizing the pressure effect on yeast.

Nutrients are required to make up strong cell walls and to keep the yeast cells alive. Depending on your wash type you may be missing essential or micro nutrients for your yeast. 100% malt or molasses fermentations are typically the most nutritionally complete and require the least amount of supplements while white sugar washes will generally only contain whatever minerals are in the water for your fermentation and will require lots of supplementation. A partial list of nutrients for yeast are nitrogen, phosphorus, potassium, sulfur, copper, iron, zinc, calcium, sodium, riboflavin, inositol, and biotin. It is a good idea to send off a sample of you wash to have it tested for these nutrients so that you can minimize you supplementation or determine that none is needed.

Adjustments to the pH of wash can be done for two main reasons. One is to prevent infections of the wash from other bacteria since the yeast strains typically prefer a lower pH range than most common airborne bacterium and the other is for flavor where the sour process or dunder pits will lower the fermentation’s pH and create continuity of flavor. Each strain will have slightly different preferred ranges but Saccharomyces Cerevisiae has been observed to have increased function as low as 4.5 pH. Maintaining and controlling pH during fermentation can result in happier yeast.

Oxygen is necessary for the development of strong cell walls. This is less critical in fermentations that are pitched at rates where little yeast multiplication is required but becomes much more substantial as the number of generations required exceeds three or if the yeast will be captured after fermentation to be repitched. Yeast – The Practical Guide to Beer Fermentation has a great write up on the effects of oxygenation as well as how to reach your desired O2 goals. This table was pulled from page 79 Figure 4.1:

Method of Aeration Observed O2 PPM
Shaking 5 minutes 2.71 ppm
30 seconds, pure O2 5.12 ppm
60 seconds, pure O2 9.2 ppm
120 seconds, pure O2 14.08 ppm


These times were for injecting 1 liter of O2 per minute into a 20 L wort. The ideal amount of O2 is 8-10 ppm so 60-seconds is about the right time. What that means for a distillery is that for 500-gallon fermentation, 25 gallons of O2 would need to be injected over 1 minute through a 0.5 micron sintered stone to reach the level required or more likely over a dozen stones. In the end getting a dissolved Oxygen meter and checking your wort after you’ve injected 25 gallons of O2 will lead you to the right solution for your process.

CO2 is a byproduct of fermentation that is toxic to yeast as it builds up and is also toxic to humans. It is necessary to vent fermenters so that the excess CO2 doesn’t build up and kill the yeast but it needs to be done in a way so that it doesn’t build up in the distillery and kill the humans.  The easy way to look at this is that 1 mole of sucrose will create two moles of ethanol and two moles of carbon dioxide. In human talk, that means that 180 pounds of sucrose will create 92 pounds of ethanol and 88 pounds of CO2. CO2 is lethal to humans at 10% with one hour of exposure so that 180 pounds of sucrose would create an environment deadly for humans after an hour if it was vented into a room that was 20’ x 20’ x 20’ with no ventilation. Depending on how long it took to convert that 180 pounds and what the air flow in that 400 SF fermentation room — that could create a dangerous situation.

Temperature control can be necessary depending on desired fermentation profile. Hotter fermentations take less time but can stress yeast and put off undesired (or desired by some) fermentations. The exponential growth phase is where yeast put off the most heat and this occurs during the first 24-48 hours of a fermentation. If temperature control is desired staggering this phase between fermenters can decrease the peak load requirements of the chillers. This phase is also when it may be ok to let fermenter temperatures increase so that the exponential growth happens quicker and then cool the fermenter into the desired range once the majority of growth has occurred but before the yeast become stressed. If attempting this it will be necessary to monitor the fermentations closely since ambient conditions can move the transition times by hours.

Other fermenter features that are used – depending on the processing of the wort – it may be worth ensuring that your fermenters have a conical bottom. A conical bottom will enable yeast and spent grain to drop to the lowest part of the tank while minimizing the volume that is contained in that lowest portion. It is most helpful when racking off of the yeast and grain to minimize the volume of wash left behind. If either the yeast and grain are being sent to the still prior to separation from the liquid or a whirlpool/mash separator are being used – then the conical bottom is of less to no use. Also, if you are using a yeast that has low flocculating tendencies where the yeast won’t drop to the bottom then the value of the conical bottom is lower as well.

The size of your fermenter depends on how it will be used. A larger fermenter to still ratio will enable multiple distillations to be pulled off of one fermenter thus minimizing the number of mashes and fermentations that are required each week. There will be changes in the flavor profile of the wash that is sitting in the fermenter all week. I would recommend people using this system to have the ability to crash their fermenter under 40°F while storing their weeks’ worth of wash.

If the fermenter and still are equally sized but the mash tun is smaller then more time will be spent on mashing than fermenting or distilling. This method can help create more continuity between mashes since they will be combined into larger batches and variations will be minimized. If the mash tun, fermenter and still are similar size then the equal focus will have to be paid to each part but it simplifies record keeping particularly if the whole system is sized to output a whole number of barrels per run.

The number of fermenters is related to both production goals and the speed of fermentation. Typically, fermentations take 3-5 days depending on the condition of the fermentation, distilleries with shorter fermentations will need fewer fermenters than those with longer fermentation and the same production goals. Due to cleanliness requirements, I typically plan one day for pumping out of fermentation and cleaning after a fermentation ends other wise starting a fermentation after pumping out and clean can cause some long days. What this means in practice is that you need one more fermenter than the average number of days in the fermentation of all of your products at least once you’re running seven days a week, with a five day, a week programs you could get by with less.

M Tu W Th F Sa Su
3 days /7 days Start Ferm 1 Start Ferm 2 Start Ferm 3 Clean Ferm 1 /Start Ferm 4 Clean Ferm 2 /Start Ferm 1 Clean Ferm 3 /Start Ferm 2 Clean Ferm 4 /Start Ferm 3
4 days /7 days Start Ferm 1 Start Ferm 2 Start Ferm 3 Start Ferm 4 Clean Ferm 1 /Start Ferm 5 Clean Ferm 2 /Start Ferm 1 Clean Ferm 3/ Start Ferm 2
5 days /7 days Start Ferm 1 Start Ferm 2 Start Ferm 3 Start Ferm 4 Start Ferm 5 Clean Ferm 1 /Start Ferm 6 Clean Ferm 2 /Start Ferm 1
3 days /5 days Start Ferm 1 /Clean Ferm 3 & 4 Start Ferm 2 Start Ferm 3 Clean Ferm 1 /Start Ferm 4 Clean Ferm 2 /Start Ferm 1
5 days /5 days Start Ferm 1 /Clean Ferm 1 Start Ferm 2 /Clean Ferm 1 Start Ferm 3 /Clean Ferm 1 Start Ferm 4 /Clean Ferm 1 Start Ferm 5 /Clean Ferm 1


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  1. Good way of explaining, and nice article to obtain data on the
    topic of my presentation subject, which i am going to convey in college.

  2. Sam Harbison says:

    Are yeast strains specifically marketed as being for use in rum washes closer to bread yeast strains or wine yeast strains? I am concerned that using a bread yeast in a rum wash may create too high a concentration of sulfur byproducts, but for the most part the hearts seem to come out fine, just more heads and tails than expected. Would using a more targeted yeast improve the hearts ratio?

    • That is hard to say there are lots of things that can cause sulphur to be produced by yeast. You are correct that bread yeasts are more prone to sulphur production but the temperature of your fermentation can also have a large impact. If you are concerned about your yeasts sulphur production specifically I’d talk to White Labs and they can give you a lot of very detailed help. If you’re looking at more general things you can do like adding packing to you still or changing how you’re running the still I can probably help there.

  3. Incredible points. Outstanding arguments. Keep up the amazing spirit.

  4. Hello there! This is my 1st comment here so I just wanted to give a quick shout out and say I really
    enjoy reading through your articles. Can you suggest any other blogs/websites/forums that deal with the same topics?
    Appreciate it!

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