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What Is Sour Mash Whiskey?

Is Jack Daniels SOur Mash Whiskey
Despite its iconic status and unique flavor, many are surprised to learn that Jack Daniel’s owes its smooth character to the traditional sour mash process

Sour mash. It’s a common phrase on American whiskey bottles, but it definitely doesn’t signify that the whiskey inside is sour. Instead, it alludes to a production process that distilleries use to regulate bacterial growth and ensure continuity from batch to batch.

What Exactly Is Sour Mash Whiskey?

Sour mash whiskey is a type of whiskey made using a method that incorporates a portion of a previously fermented mash into a new batch. This technique, similar to making sourdough bread, helps maintain consistent acidity levels in the mash, ensuring a stable and efficient fermentation process. Although the name suggests a sour flavor, it actually refers to the process rather than the taste of the whiskey. Sour mash is widely used in the production of American whiskeys, like bourbon and Tennessee whiskey, to achieve consistent quality and flavor across batches.

Let’s Get More Technical

A “mash” in the world of whiskey refers to the mixture of grain, water, and yeast that is initially fermented to produce alcohol. Distillers are very careful to regulate the pH of their mash; if it gets too high (basic), unwanted bacterial growth can occur.

Fortunately, the distillery environment offers an abundant source of pH-lowering substance: spent mash, also called backset or stillage. This is the acidic, nutrient-rich substance that’s left behind in the still after a distillation run is complete. By adding a portion of that spent mash to their current mash (the remainder is often fed to livestock), distillers can ensure their mash pH remains within acceptable levels and ensure flavor continuity from batch to batch.

Distilleries add more backset to their current mashes than you might expect—Chuck Cowdery reports that most distilleries use a 1:3 or 1:4 ratio of backset to new mash. (In the linked story, he also outlines another interesting way that distillers could sour their mash–by letting the mash sit for a few days before distillation and allowing microorganisms to do their work.)

It’s also worth noting that virtually all major bourbon and Tennessee whiskey distillers use the sour mash technique, even though only a portion of them actively market their whiskeys as “sour mash.”

Techniques similar to the sour mash technique are also used at many Jamaican rum distilleries, only there, distillers age their backset anaerobically (sometimes seeded with organic matter like fruit) before adding it to their mashes. This aged backset is called dunder, and its aroma can be truly shocking. However, distillation manages to transform those off-putting smells into the intense, fruity esters Jamaican rum is known for.

What Whiskies Are Made Using The Sour Mash Process

A lot of your favourite brands all use the sour mash process.  The reason being that the sour mash process helps ensure consistency in pH levels during fermentation, leading to a stable and predictable fermentation environment. This consistency is crucial for maintaining the distinct flavor profiles and quality that these brands are known for.  Click the links to search The Whiskey Wash archives and to learn more about your favourite brands.

What Whiskey Is Not Sour Mash?

Finding American whiskies that explicitly do not use the sour mash process can be a bit challenging, as the sour mash technique is prevalent in the production of many American whiskies, especially bourbons and Tennessee whiskies, for consistency and quality control. However, there are craft distilleries and specific products that may not adhere strictly to the sour mash process or emphasize different production techniques. Here’s a general list of American whiskey styles or examples where the sour mash process might not be a focal point:

  • Single Malt Whiskies: American single malt whiskies, inspired by Scottish tradition, focus more on the malted barley and distillation process rather than fermentation techniques like sour mash.
  • Some Craft Distillery Products: A number of small, artisanal producers experiment with unique fermentation processes, including non-sour mash techniques, to create distinctive flavors.
  • White Whiskey and Moonshine: These unaged or lightly aged spirits, while not always marketed under strict definitions, often prioritize quick production and may skip the sour mash process.
  • Experimental and Limited Edition Releases: Distilleries occasionally release products that explore different grains, fermentation processes, and aging techniques, some of which may not use the sour mash method.

Margarett Waterbury

Margarett Waterbury is the author of Scotch: A Complete Introduction to Scotland's Whiskies and a full-time freelance writer and editor. Her work has appeared in Whisky Advocate, Food and Wine, Spirited Magazine, Artisan Spirit, Edible Seattle, Sip Northwest, Civil Eats, Travel Oregon, Artisan Spirit, and many other publications. She is the former managing editor of Edible Portland, as well as a cofounder and former managing editor of The Whiskey Wash. In 2017, Margarett won the Alan Lodge Young Drinks Writer of the Year award. She received a fellowship for the Symposium for Professional Wine Writers in 2017 and 2019.

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