March 1, 2009

Sour Mash Method Explained

Several bourbons indicate "Sour Mash" on their labels or otherwise indicate that the sour mash method was used in the creation of that bourbon. So what does that mean?

To understand what sour mash is, you first have to understand the term "mash." At the beginning of the distillation process of bourbon, cornmeal and water are mixed together at a high temperature. The temperature is then lowered, and then either rye or wheat is added depending on the bourbon. The rye or wheat are the "flavor grains," so using one or the other has an impact on the flavor profile of the final product. The temperature is once again reduced when malted barely is added. The barley is added because it releases enzymes that are necessary to convert starches into sugars, which is essential in distillation. Once all these ingredients are together, mixing a big tank at the distillery, it becomes the mash.

After sufficently mixed, the mash then goes onto the fermentation process where all the alcohol is distilled from the mash. The stuff left over after all the alcohol is distilled is known as the sour mash due to its sour flavor.

The sour mash, also called backset and spent mash among others, is then introduced to a new batch of mash when entering the fermentation process. So, sour mash is fermented mash that is left over from a previous distillation that is added to a new distillation. The process is used to control the acidity levels of subsequent fermentations, which in turn helps ensure that each distillation is consistent in flavor.

The Sour Mash method is used in the distillation of many bourbons, including Ancient Age, Evan Williams, Woodford Reserve, Knob Creek, Maker's Mark, Wild Turkey, and Old Fitzgerald. It's a very traditional way of bourbon production, still used today despite modern technology's creation of alternate methods. This adherence to tradition and heritage is one reason I enjoy American whiskey so much. Cheers.


  1. Good article. Just one minor correction of fact. The term "sour" mash has nothing to do with any sour taste of the recycled mash. It gets its name from the fact that the process was developed based on methods used for making sourdough bread. Sourdough bread follows a similar method of using a prefermented starter with the new dough. Sourdough gets it's name from the flavor of the final product, but sour mash just gets it's name from copying the process from the other. The starter mash that is used in the sour mash process can actually be quite sweet sometimes.

    It's a very common mistake to make though, and the article is still very well written.

  2. I think these old brands like beam, dickel, etc still use the same yeast strain they have used for 100's of years.

  3. The author is confused in his terminology.......... In the fermentation process sugars are processed by the yeast to create alcohol. Alcohol is distilled in the distillation process AFTER fermentation. Also the mash is left over from previous mashing........not from distillation. In the distillation process temperatures are raised to the point where all bacterial and yeasts are killed. Sour Mashing is very much equivalent to the sour dough process used to make bread. You obviously cannot start a new batch by using a piece of baked bread anymore than you can start a mashing process after distillation!

  4. Very well said, Anonymous 12/16/12... it's the small portion of fermented mash, which is taken before distillation, and after fermentation, which is used to start the next batch of fermentation. Often times, this yeast-laden fermented mash is added to a small amount of new mash material, to create a larger batch of yeast, before adding to the entire mash kettle.

  5. Mertmeister and Anonymous 12/16/12 are incorrect. The backset comes out of the bottom of the first column of the still, and has been passed through live steam. It has no active yeast in it. The purpose of sour mashing is to increase acidity (making the new mash sour) and feed the new yeast (which like to eat dead yeast). The backset does not start the new fermentation.

  6. Not a baker, so I reckon I can't comment about sourdough but sour mash I do know. You mix your grain with equal amount of sugar add water, yeast and ferment and distill. You throw out the first 3-5 ounces (methanol) and catch the rest up to 208 degrees and then shut it down. None of this is for drinking, though it is drinkable. Now remove half the spent grain from fermenter and add back the same amount and add less say 3 gallons of water. Now take out 2 gallons of whatever (we call it slop) you have left in your pot (still) and add your sugar stir to dissolve and pour this back into the fermenter. Stir for about 15 minutes and pitch your yeast and stir gently for another 15 minutes, cover, airlock and let it do it's thing. Let it sit a day after all the bubbling has stopped (or up to 2 weeks if your of a mind to). Drain, strain and fill pot and add all the liquor from the stripping run into the pot and fire it up. Now once again toss the first 3-5 ounces and now you have sour mash dripping into a jar. To achieve the same flavor, you keep repeating the same process and by the third or fourth generation, you will have your brand of sour mash. The ratio of water to slop/backset is up to you, never more than 50/50 and never less 75/25. 60/40 is my ratio.