Mash Cooking & Fermentation

And now we get to enter chemistry class. We’ve talked about grains we use, so let’s talk about the next step: mash cooking and the fermentation process.

Mash cooking (“mashing”) can be explained simply, or you can get specific and dive into the specific chemistry of cellular breakdown, how water temperature and the amount of water used affects the cooking process, and more. For the sake of brevity, we’ll keep things relatively simple in this article, but know that there is a ton of information out there if you want to dig in further. Here are a few places to start.


Ok, so our end goal is to create alcohol that we can then distill, age, and drink, right? Alcohol is a byproduct of yeast eating sugar, which is basically what is referred to as the fermentation process. Prior to fermentation, the starches in the grains need to be broken down into sugars, which creates a thick product called “mash."


After we choose our grains, we mill them, which means depending on the spirit, we grind them into varying levels of granularity/powder.


We use a vessel called a “mash tun” to cook our grains. To start, we fill the mash tun with hot water. Then we dump in our milled grains and add some enzymes. These enzymes act as a catalyst to help, along with the addition of the hot water, break down the cellular structure of our grains into sugar. Then we let our mixture of hot water, grains, and enzymes (this is our “mash”) sit for a bit.


After the mash has rested for the initial amount of time in the mash tun, we turn the heat back on and bring the mixture to a boil again. We repeat this process a few times - heat and let our mash sit - hitting various temperatures and resting times. Once we feel the mash is ready to start the fermentation process, we transfer the mixture into an open top fermenter.


Fermentation takes time. Once we transfer our mash to the open top fermenter, we cool the mash down to a specific temperature and then we add one final enzyme which is basically a yeast nutrient - it makes the yeast more hungry. Then we continue to cool the mixture. Because yeast is living, if we don’t cool the mash before adding the yeast, we risk killing the yeast.


When we reach our desired temperature, we add our yeast, give our mixture a quick stir, and let it sit for 3-5 days. During this resting process, the yeast will do its thing by eating the sugars from the mash and create alcohol. Once we've fermented to the desired level we are targeting, we distill.


As mentioned earlier, there is both a science and an art to what temperature you boil your mash to and how long you rest your mash. While there are general standards you can follow, each distiller/distillery will have their own feel to the process, and this is one of the areas where distillers get to play and have their own style.


Next up: The Distillation Process


If you missed our previous posts as we unveil the steps taken to make our soon to be released Trestle American Single Malt Whiskey, check them out:

  1. How We Create a New Whiskey

  2. What Spirits are we Making and Why?

  3. What is an American Single Malt Whiskey?

  4. Raw Materials for Making Whiskey