I'm brewing a Belgian golden strong ale for the first time. According to the fermentation schedule, it should cold crash and lager at 32°F (0°C) for three weeks. Even though I've cold crashed before, my technique has been to momentarily replace the airlock with sanitized foil. Keeping the airlock while cooling will suck water into the tank. A similar approach is mentioned in Lager Diacetyl Rest and Lagering Without Air Escape.

  • Is there a better way to do this using a glass carboy?
  • Is there a risk of oxidation since oxygen will enter the tank?

2 Answers 2


This is a valid way to do it.

There will be a slight amount of air and therefore oxygen sucked in, but not enough that I would worry about it.


Keep in mind that the CO2 is heavier than any oxygen that may be pulled in from cold crashing. That CO2 "blanket" at the beer's surface should keep the O2 from affecting your beer. Or if your fermentation is complete, you could even cap the tank during cold crash and prevent the O2 from getting in at all.

  • I had read that pressure will implode a glass carboy. Hence, I refrained from doing so. I have caps, so it might be worth a try given sage conditions.
    – Martin
    Mar 29, 2018 at 16:50
  • This is wishful thinking. The oxygen will diffuse into the CO2. If gasses separated out based on density all oxygen breathing life on Earth would have suffocated long ago. Apr 1, 2018 at 7:00
  • There's no wind in a carboy? May 1, 2018 at 17:06

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