"Sour mash" is one of those terms that sounds like a flavor descriptor but isn't. It refers to a fermentation technique, not a taste profile. And here's the thing: nearly every bourbon you've ever drunk was made with sour mash — most producers just don't put it on the label.

What Sour Mash Actually Means

When a distillery makes a new batch of whiskey, it has leftover liquid from the previous distillation run — the spent, acidic byproduct called "backset" or "setback." In the sour mash process, a portion of that backset is added to the fresh grain mash before fermentation begins.

That backset is acidic — hence "sour." Adding it to the new batch lowers the pH of the mash, which does two important things: it creates a hostile environment for unwanted bacteria, and it gives the distiller a consistent starting point from batch to batch. The yeast, working in a predictable environment, produces a predictable fermentation. Batch 1,000 tastes like Batch 1.

The Alternative: Sweet Mash

The opposite of sour mash is sweet mash — no backset, just fresh grain and fresh yeast every time. Sweet mash fermentations are less stable, more susceptible to microbial contamination, and harder to keep consistent. That's exactly why sour mash became the industry standard over the last two centuries.

True sweet mash whiskeys exist, but they're rare. Makers Mark and Woodford Reserve are two well-known names that have experimented with sweet mash expressions — usually as limited releases specifically because the technique is so unpredictable.

Why Michter's Calls It Out

If almost everyone uses sour mash, why does Michter's put it on the label? Because for most of the industry, it's background process — assumed, unremarkable. Michter's leaning into it is a positioning move: they're telling you this whiskey was made with care toward consistency and craft, not just grain-to-glass efficiency. Whether you find that compelling or eye-roll-worthy probably depends on how many marketing decks you've read this year.

Worth noting: Jack Daniel's Tennessee Whiskey also makes sour mash a centerpiece of its identity — the Lincoln County Process (charcoal filtering) gets more attention, but the sour mash fermentation is baked into their story too.

Does It Affect the Taste?

Not directly. Sour mash is a process control tool, not a flavor driver. It influences the fermentation environment, which can affect ester and congener development — but tracing those effects through distillation and years of barrel aging is nearly impossible in the finished glass.

What it does affect: consistency. When you open a bottle of Michter's US*1 Sour Mash and it tastes like you expected, sour mash fermentation is part of why.

The Bottom Line

Sour mash is how almost all American whiskey is made. It's a practical technique that keeps fermentation stable and flavor consistent from batch to batch. When you see it on a label, you're not being told something exotic — you're being told the distillery is proud of their process. That's worth knowing before you decide how much weight to give it.

If you want to see how it shows up in the glass, the Michter's US*1 Original Sour Mash review is a good place to start.