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I’m using lactic fermentation to make a batch of sauerkraut, fermented berries, etc. Rather than going the glass jar route I’ve placed everything in a vacuum sealed bag. This is a technique which Noma uses.

Over the next few days the contents will create a large balloon of carbon dioxide within the bag. Can the exposure to carbon dioxide spoil the contents, in the same way that exposure to air would?

Example image: enter image description here

Would it be feasible to “burp” the bag, freeze the contents, vacuum, then allow to thaw to continue the ferment? This way I would be able to reseal the bag without worrying about the wet juices being sucked out by the vacuum sealer.

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    In general, modifying a tested food preservation recipe is a bad idea. If it comes from a trusted source, follow it exactly. If it's not from a trusted source, find a different recipe.
    – user141592
    Jun 13, 2020 at 17:15
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    The recipe will not be modified. I am however wondering if the presence of carbon dioxide comprises an aerobic environment which can cause spoilage. As for the freezing portion, I know that frozen ingredients can be used during the start of the process, and that refrigeration can be used during the process, but I find no comments on freezing rather than refrigeration and if lactobacillus would survive that process.
    – Halaster
    Jun 13, 2020 at 18:05
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    If the recipe doesn't call for burping the bag, then don't. An aerobic environment refers to an environment with free oxygen, not an environment with carbon dioxide.
    – user141592
    Jun 13, 2020 at 18:48
  • That’s a great point, thanks. The recipe does call for burping and resealing if the bag looks like it might burst. However with all the wet contents I can’t really vacuum seal it, hence I was considering freezing it to help create a vacuum.
    – Halaster
    Jun 13, 2020 at 19:01

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Great question!

Firstly, the build up of carbon dioxide should not jeopardize the ferment in any way. In fact, it probably serves to protect your ferment further from going bad or taking a turn in the wrong direction. Lactic acid bacteria grow under anaerobic conditions (absence of oxygen) during lacto-fermentation. These are the microbes that you really want to have thriving on the fruit or vegetable in the bag. As more carbon dioxide builds up in the bag, it further inhibits the growth of other competing aerobic microbes (that require oxygen to grow) such as mould that would spoil the ferment, encouraging lactic acid bacteria to prevail and dominate.

Secondly, you should not really have too much problems with running the vacuum sealer unless there is really a huge amount of liquid. You could pour out some of the excess liquid to reduce the level in the bag before resealing. You may also try sealing with a weaker suction.

I would strongly advise against freezing and then thawing the ferment. The freeze thaw process would affect the viability of the microbes and you would end up with a handicapped ferment as some proportion of the microbial population would die off as they are being frozen. You should only freeze your ferment for storage after it has reached your desired end state.

In fact, burping is probably not necessary if your ferment progresses fast enough to reach your desired end maturity. By then you would be concluding the ferment by cutting open the bag to harvest the contents.

Ultimately, I think the purpose of burping is simply to prevent the bag from bursting due to excess gas build-up.

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