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John Palmer on Diacetyl rest?

Hello I been reading through john palmer 4th edition of How to Brew. An I came across what he recommend for when to do a Diacetyl rest an he say Lager’s in table 6.2 the suggestion is to raise the temperature of the fermentation by 14-18f around day 4 , assuming that the high-growth phase (steady bubbling in the airlock) is going to last until day 6, you would then raise the temperature for the Diacetyl rest. In his book this information is on page 94 of 582. I also know he said to preform a Diacetyl rest when your 2 to 5 gravity points from FG but my question is he said to raise your lager temp on day 4 but I thought with lager’s it take a lot long to reach the 2 to 5 gravity points from the final gravity for the Diacetyl rest ?

I just wait until it slows down and warm it. You can’t really count days to many variables.

  1. Diacetyl rest is only needed if you actually smell or taste diacetyl after a few days into fermentation. If you try a sample after several days into fermentation and do not smell or taste any buttery or butterscotch notes, then it is safe to just leave it alone. I only get diacetyl on my lagers about half the time or less than half the time.

  2. If you decide that you do need to do a diacetyl rest, you’ll want to do it when the specific gravity points are about half of what you started with. So for example, for a 1.050 lager, you should try to start the d rest when specific gravity is at about 1.025 plus or minus a few points.

Number of days doesn’t matter. The degree of fermentation according to specific gravity is what matters.

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