I've fermented a 5 gallon lager at 45°F(7°C) for 2 weeks. The OG 1.050 and FG 1.012. At this point, I racked to secondary and put back in the airlock & bung. Increasing temperature to 65°F(18°C) for 2 days. I plan to lower gradually in secondary 5°F(2.5°C) per day until reaching 35°F(2°C) or so for lagering several weeks.

1) Will I notice any airlock activity during diacetyl rest? How else to determine diacetyl rest is occurring?

2) Will I remove airlock during lagering and keep airtight with bung so no air escapes?

1 Answer 1


Your diacetyl rest should be the last couple days of your primary

1) Yes there should be air lock activity as the added heat will give the yeast a boost in activity to clean up the diacetyl precursors.

2) The idea of a slow approach to lager temp is two fold, 1 to allow CO2 production to compensate for gas temp shrinkage and prevent airlock suck back. 2 to allow a gentel change to the yeast doesn't crash out.

Typically I will remove the air lock and wrap the carboy neck in sanitizes foil, to eliminate the suck back risk, on getting to lager temp. Once to temp put the airlock back on.

If you put a plug in, and drop temp too fast it may suck into the carboy.

  • Thanks for the response. It's funny, while cleaning the primary glass carboy with warmer temperatures and putting the plug in, it ended up sucking the plug into the empty primary glass carboy, which gave me a challenge of pulling that thing out with needle-neck pliers. Just a side note. I like the idea of wrapping in foil until reaching 35 degrees F, and then reinserting the airlock at that time. Thanks
    – nhunsaker
    Jan 30, 2016 at 20:28

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