Hops get plenty of attention. Malt brings the grain, the color, and much of beer’s backbone. But yeast? Yeast is the tiny living ingredient that turns a brewer’s hard work into beer.

Its main job sounds simple: consume sugar and produce alcohol and carbon dioxide. Along the way, it also helps shape how a beer smells, tastes, and finishes. That’s a pretty big contribution from something you can’t see without a microscope.

Let’s give yeast a little credit.

Before yeast gets involved, brewers make a sweet liquid called wort (pronounced “wert”). During the mash, enzymes break down starches in the grain into sugars. The brewer then separates that liquid from the grain, boils it with hops, and cools it before adding yeast.

That’s when fermentation begins. Yeast uses the fermentable sugars in the wort, producing alcohol and carbon dioxide in the process. The alcohol stays in the beer. The carbon dioxide can escape during fermentation or be captured to help carbonate it; brewers can also add carbonation later.

But making alcohol is only part of the story.

Ever smelled banana in a wheat beer that didn’t have bananas in the recipe? Yeast may be responsible. Certain strains produce aromatic compounds called esters, which can give beer fruity notes. Some strains also produce spicy compounds called phenols, including the clove-like character associated with certain wheat beers.

Those flavors can come from fermentation itself. No fruit bowl or spice rack required. Different yeast strains produce different combinations of these compounds, giving brewers another way to shape a beer’s personality.

Sometimes, though, a brewer wants yeast to keep a lower profile. A more restrained fermentation character lets other ingredients take center stage: the toastiness of malt, for example, or the citrus aroma of hops.

This is also where the distinction between ales and lagers comes in. They generally use different types of brewing yeast. Ale fermentation usually happens at warmer temperatures, while lager fermentation typically happens cooler. Those yeast choices and conditions help create different flavor profiles, although there’s plenty of variety within both families.

Yeast strains also differ in how much of the wort’s sugar they can ferment. That helps influence the beer’s strength and whether it finishes relatively dry or retains more sweetness and fullness. The recipe matters, too; yeast is one member of the brewing team.

Because yeast is alive, brewers have to give it the right conditions to work.

Temperature is a big one. Fermentation creates heat, and changes in temperature can change the flavors yeast produces. Warmer doesn’t automatically mean better or worse; the right temperature depends on the strain and the beer the brewer wants to make. Keeping fermentation under control helps turn a good recipe into a consistent pint.

So, what does yeast actually do? It turns sugary wort into beer, makes alcohol and carbon dioxide, and contributes flavors that help make each style recognizable.

The next time you enjoy a Walnut River beer, take a moment before that first sip. Notice the aroma, then pay attention to the flavor and the finish. Some of what you’re enjoying started with a microscopic organism getting to work.

Small ingredient. Big job. We’ll drink to that.