Adjunct
Lactose
Milk-derived sugar that brewing yeast cannot ferment, leaving sweetness and body in the finished beer.
Brewing yeast cannot ferment lactose. It has no enzyme for it, so whatever goes in stays in as sweetness and body, and that is the entire reason it is used. It is what makes a sweet stout sweet and what gives a milkshake IPA its weight.
Two consequences follow. A hydrometer cannot tell lactose apart from unfermented wort sugar, so a lactose beer's apparent attenuation and calculated ABV both read wrong unless the brewer accounts for it. And because it is a milk derivative, a beer containing it is not vegan and not suitable for anyone avoiding dairy — which is worth knowing, because the label does not always make it obvious.
What it is for
Lactose. Milk sugar, which brewing yeast cannot ferment. It stays in the beer as sweetness and body, and it makes the beer unsuitable for anyone avoiding dairy.
- Adds unfermentable sweetness
- Builds body and mouthfeel
Whether it ferments
| Fermentable | No — brewing yeast cannot take it, so whatever goes in stays in. It contributes flavour, and where it is a sugar, sweetness and body that survive into the glass. |
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Beers containing lactose are not vegan and are unsuitable for anyone avoiding lactose. Labelling is inconsistent across sweet stout, milkshake IPA and pastry stout.
What it contributes
The contribution of the ingredient, not the profile of a finished beer. How much of it reaches the glass depends on quantity, timing and what else is in the recipe.
Styles it defines
- Milkshake IPA
A hazy IPA with lactose and fruit added for sweetness and a fuller, creamier body.
- Sweet stout
A stout sweetened with lactose, giving chocolate and cream character over a full body and gentle roast.
- Pastry stout
A heavily adjuncted sweet stout built to taste like dessert, using lactose, vanilla, cocoa and similar additions.
- Kettle sour
Beer soured with Lactobacillus in the kettle over hours rather than months, then boiled and fermented normally — usually fruited.
Styles where this is characteristic rather than optional. Plenty of other beers use it — these are the ones that would not be themselves without it.