is a diacetyl rest needs if fermenting under pressure at ale temps?

[odie]

I'm fermenting a lager under pressure. About 7 psi and 67 degrees. Is a diacetyl rest even needed since my fermentation temps are elevated?

Or can I just leave if alone until it reaches final gravity and then drink right away?

 

[Spundit]

Typically a diacetyl rest would involve raising the temp and letting it sit for a few days. In your case, I would not increase the temp.... But I always let beers sit for a couple days after final gravity is reached. Just a simple practice to help ensure the yeast have cleaned up everything they can.

If you are in a rush, you could taste the beer to ensure nothing tastes off before you package it. That is always an option.

 

[Craiginthecorn]

Diacetyl is cleaned up more quickly at ale temps, but certain yeast strains generate more then others. It is possible that you'll have diacetyl or, more likely, precursors remaining. Do a forced diacetyl test. A quick Google search will reveal several articles about it, but regardless of process, I like this suggestion from Josh Weikert of Beer & Brewing to have a control sample:

"From your primary fermentor, draw two samples into two jars and seal the jars. Heat one of those jars (a hot-water bath works well) to about 140°F (60°C). Hold it there for about fifteen minutes, then cool to the same temperature as your unheated sample. Now, smell/taste both. If they taste the same, then you’re in the clear! There’s likely very little chance of a meaningful diacetyl flavor. However, if the heated beer tastes strongly of diacetyl, you should let the yeast continue to work on it (and maybe increase the temperature a bit to goose the yeast cells into activity)."

 

[cactusgarrett]

Facetious answer: it's needed if it's needed.

Whether diacetyl (precursors) is generated (and how well it's cleaned up) depends on everything that goes into the recipe: process as well as ingredients. You don't know for sure if a d-rest is needed unless diacetyl is actually present. That said, to do it is easy insurance.

 

[DuncB]

Agree good insurance to do it, don't be scared of bumping the pressure up, if near end of ferment set spund to vols target for that temperature.