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Old 09-08-2011, 10:42 PM   #1
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Default Effect of temperature and pressure during fermentation to reduce/remove diacetyl rest

I've now completed three lagers, Pilsner, Helles, Dark Lager with different yeasts, using pressure fermentation techniques. The yeasts were all built up from starters, the wort oxygenated via SS stone and O2 bottle, pitched and fermented at a target temp of 48 deg. The pressure rates were 2psi through 50% fermentation, ramped to 10psi to 75% fermentation, then ramped to 16psi and temp reduced over 2 days to 33 degrees.

Once at 33 degrees, I'll take a larger sample de-gas, use my hydrometer for a proper reading(refractometer used prior), and taste. I'm very familiar with the buttery feel/taste associated with Diacetyl and not one of my lagers has shown any signs.

I'm fully comfortable with the if it ain't broke policy but I wanted to put it to the more scientific folks within this forum to get your thoughts. The reason is it is quite a challenge to bring 10 gallons from 48 degrees to 58 or higher without using a heat source.

Is there any science to this or have I stumbled onto a good routine and I'll keep it routine?

Matt

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Old 09-08-2011, 11:35 PM   #2
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No question that temperature has a profound effect on how yeast perform and pressure does too though it's not as dramatic. Mega breweries use unitanks so large that they worry about the effects of hydrostatic pressure on the yeast at the bottom. I know very little about this except that I seem to recall seeing that pressure is not good for yeast. Nonetheless I also seem to remember that lagering is often carried out at a couple of psi positive pressure and they wouldn't do that if there weren't benefit.

All this aside, if you manage a lager fermentation properly i.e. pitch and ferment at a low temperature, hold under 50 °F until within a couple of °P of terminal, slowly cool down to near freezing, condition there for a couple of weeks and then transfer to kegs with a lot of yeast you should have no problem with diacetyl (assuming, of course, that the yeast were healthy, pitched in proper quantity and were not contaiminated).

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Old 09-11-2011, 08:32 PM   #3
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Thx for the note. I definitely built a great starter and i just tasted a sample. It's coming out nicely.

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