Can Yeast Metabolize Lactose?

(This is an Oculyze Yeast Glossary entry)

This is a question you certainly stumbled upon if you’ve ever considered experimenting with adding lactose to your beer. Because, yes, some brewers do that. Lactose is added to beer for sweetness, but also for that milky mouthfeel. Additionally, lactose can complement certain notes, such as malt and chocolate, but also fruity flavors, for a more milkshake-y experience.

So, can yeast metabolize lactose? No, it cannot. It is actually why brewers can play with it as they wish, without the fear of messing up the fermentation process.

Yeast typically uses monosaccharides such as glucose, fructose, and maltose to satisfy its energy needs and lactose is a disaccharide composed of glucose and galactose. Yeast lacks the necessary enzymes to break down lactose into its constituent sugars, and therefore cannot metabolize it.

So while lactose can be broken down by some bacteria, such as lactobacilli, it cannot be metabolized by yeast.

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