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I am bottle-conditioning and storing beer in a storage room with temperatures reaching as low as -5°C (significantly below the freezing temperature of water). There are few sudden changes in temperature, and the beer itself does not seem to freeze inside the bottles. Already-carbonated beer that has been left there as the temperature have fallen tastes fine, but I am curious however as to what impact these kind of temperatures have on the beer - especially since I now want to bottle-condition some freshly brewed beer.

  • Will the yeast survive below-zero temperatures?
  • What eventual effects might below-zero storage have on the yeast if it recovers?
  • Would there be a difference when it comes to the type of yeast (e.g. top vs bottom fermenters etc.), or is this irrelevant at these temperatures?
  • Will maturation be harmed, and in what way?
  • Will the beer be affected by below-zero storage in other ways?

Looking forward to your comments and answers.

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It's fairly safe to say that bottle conditioning at -5°c will not yield good results.

Even high ABV beers stored below freezing will form ice crystals and force a separation of the water and ethanol. (Eisbock)

While many yeasts can survive freezing temperatures the become dormant or have their metabolism slowed down so much they no longer perform useful fuctions to a brewer.

Also if ice crystals are forming they also can form in the water inside the yeast cell and rupture the cell wall, killing the yeast.

Also you run the risk of bottles breaking or caps popping from ice expansion.

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I am assuming you are saying for a few days it will be this cold, not permenatly. If you hope to get carbonation with long term sub zero storage it is unlikly to work for the reasons of slowed metabolism laid out by EZ.

I will try cover all your questions:

  • Will the yeast survive below-zero temperatures?

Yes, most of it will some of it will not, yeast is pretty hardy but repeated freezing and thawing will kill off some of the yeast.

  • What eventual effects might below-zero storage have on the yeast if it recovers?

It will select for yeast cells with a stronger cold stress response.

  • Would there be a difference when it comes to the type of yeast (e.g. top vs bottom fermenters etc.), or is this irrelevant at these temperatures?

I would guess that lager yeast may be more resistant to these low temperatures but that is purely guess work based on the fact they derive from a strain of yeast from high mountain regions.

  • Will maturation be harmed, and in what way?

It may be harmed but the lower the temperature the longer you will need to reach desired carbonation and conditioning levels.

  • Will the beer be affected by below-zero storage in other ways?

I have accidentally frozen and thawed beer before and the flavour was not as expected, it had taken on an unplesant bitterness. But just making the beer cold without freezing should not affect it.

You may slow the degradation of fresh hop charchter by keeping it so cold, so there may be some unexpected benefits.

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