Most of my knowledge of diactyl rests come from Palmer's How to Brew, and it applies entirely to lagers. It mainly means bringing the temperature up slowly and letting the lager sit at a slightly higher temperature for a couple of days so the yeast consume the diacetyl produced in the cold fermentation.

Wyeast recommends a thorough diacetyl rest with their ESB yeast, though, and I wonder what in the heck this means.

A very good cask conditioned ale strain, this extremely flocculant yeast produces distinctly malty beers. Attenuation levels are typically less than most other yeast strains which results in a slightly sweeter finish. Ales produced with this strain tend to be fruity, increasingly so with higher fermentation temperatures of 70-74°F (21-23° C). A thorough diacetyl rest is recommended after fermentation is complete. Bright beers are easily achieved within days without any filtration.

What if I'm fermenting at the top of the range anyway?

2 Answers 2


You can always take a gravity reading and taste the beer to determine if you even need to do a diacetyl rest. When you raise the temps on a lager for a diacetyl rest, the purpose is to make the yeast more active in order to reduce the diacetyl. Even if the yeast is less active, giving it more time accomplishes the same thing. That's true of ales, too. You can't really raise the temps, but you can leave the beer on the yeast for more time. In effect, you're doing a diacetyl rest by doing nothing!


I usually take that to mean "hold the temperature at its high point for an extra day or three after the fermentation activity has mostly stopped" (i.e. don't let it peak and fall back down too quickly).

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