The Science-y Reason Your Beer Smells The Way It Does

April 30, 2017

Ever taken a whiff of a Belgian witbier and smelled a distinctive banana aroma, even when no bananas are in sight? Or maybe you’ve noticed that some IPAs give off a scent exactly like a piney forest floor in October. Where do those scents come from? Many beers attain their aromas from beer’s four primary ingredients alone—water, malt, yeast, and hops— but some contain actual spices, herbs, fruits, and even vegetables.

What's that aroma? Photo by Mark Weinberg

For starters, gently-spiced ales have a long history in Belgium where the renowned witbier is traditionally brewed with coriander and orange peel. Germans too—despite centuries under the restrictive Reinheitsgebot, or “beer purity law”—sometimes add spices to ales like Gose which contains coriander and salt. British- and Belgian-style Christmas ales and winter warmers are more heavily spiced and often feature cloves, cinnamon, nutmeg, and cardamom.

Fruit-infused sour ales and IPAs, as well as vegetable-infused ales, are now some of the most popular styles in the States, but fruity, spice-like aromas can also result just from fermentation. Esters and phenols are two of several products of fermentation in which yeasts convert the sugars in unfermented beer into alcohol and carbon dioxide. Belgian ale yeast strains are notorious for producing complex spice and fruit aromas while German strains, like ones used for hefeweizen, result in a distinctive clove-like scent from phenols. Other strains like Brettanomyces—common in Lambics and Flanders red ales—add a funky, barnyard-like bouquet. Lagers, fermented at much lower temperatures than ales and with a different yeast strain, are clean-fermented and rarely display overt ester or phenol aromas like those found in ales. Hops, particularly American, Australian, and New Zealand varieties, add huge aromas of grapefruit, lime, gooseberry, pine, tropical fruits, and ever white wine to beer , all originating from their own inherent chemical compounds rather than from additional fruits or spices.

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So, next time you sniff your brew, trade thoughts on the scents with your drinking partner—it's a good way to test your nose and apply your learnings to other beers.

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