Are my homemade pickles supposed to fizz like a soda on opening?
September 27, 2020 7:05 AM   Subscribe

A few weeks ago I bought a jar of homemade pickles from a stand on the side of the road. It's been sitting in a dark cupboard since. On opening today, it made a distinct popping sound and bubbles evolved from the pickling liquid for a couple of minutes, similar to CO2 outgassing when opening a bottle of soda. It is clear that some kind of fermentation has been going on since the lid was closed. Is there any kind of pickling process where this is a normal result or is this a clear indication of bad things happening?

It's a half liter clear glass jar filled with whole small green tomatoes, small onions, disks of carrot and what looks like celery leaves. The liquid is transparent but not entirely clear and leaves enough headspace in the jar that the very top of the pickles is uncovered. The cap was screwed on tight, but looks like it's been on there for a while - would not be surprised if this was from last year's harvest. I didn't get any noticeable odor on opening the jar, and I'm not getting any funny smells from the pickles.

Please note that I understand discarding it is safer than eating it, I don't need to be reminded thank you very much. Also I have not tasted anything yet and understand that food poisoning is serious business and no fun at all.

My question is if this *could* be a normal result of the pickling process, and any information you might have on what that process would be.
posted by each day we work to Food & Drink (16 answers total)
Best answer: Traditional pickles are fermented and can fizz when opened. A dead giveaway that you have fermented pickles is that the liquid is kind of murky-white.

We are more used to vinegar pickles, which are not fermented and do not fizz.
posted by slkinsey at 7:11 AM on September 27, 2020 [5 favorites]

I think this is a bad sign, sorry. I have been checking in various home-canning forums and they all have warnings against fizzy pickles - it's a sign of some kind of bacterial activity, and the particular kind of bacteria that it might be could be dangerous.
posted by EmpressCallipygos at 7:36 AM on September 27, 2020 [5 favorites]

I've definitely bought fermented (not vinegar- but salt-based) pickles before that has some pressure build up / fizziness. It's also standard in other fermentation processes I'm aware of like picking lemons. If you're not trying for it, like if your pickle recipe doesn't have the right chemistry for safe fermentation while killing botulism, it would be bad.

One way to tell would be the container: if it's labeled with something about pressure/fizz, or if it has a pinhole poked in the lid to avoid explosive build up.
posted by Lady Li at 7:47 AM on September 27, 2020 [1 favorite]

Short answer: unless the labeling says it's supposed to fizz, assume something has gone wrong.

Long answer:

If something is supposed to be under a vacuum seal, fizzing is a very bad sign. For instance, if it's commercially processed in a jar with a pop-up-button lid, or if it was pressure-canned or hot-water canned in a Mason jar, it absolutely should not fizz. Those kinds of processing are supposed to kill microorganisms, and if anything has survived or snuck in that can produce CO2, something is wrong.

On the other hand, if a ferment with live culture is packed without heat — just poured or stuffed into a jar at room temperature, and a lid screwed on — then popping and fizzing can be okay. Kimchi in a jar often isn't heat-treated in any way, and so often has live culture, and it can be really vigorously fizzy when you open it.

Commercial stuff with live culture tends to go way out of its way to tell you about that. My grocery store kimchi brand is all WARNING! THIS WILL FIZZ AND POP WHEN YOU OPEN IT! THAT IS NORMAL! on the lid. A responsible farm stand would do the same thing on a live culture pickle jar. So if there's nothing on it that indicates that it's supposed to do this, and it wasn't specifically sold as having live culture, you should be on the conservative side and assume that something's gone wrong.
posted by nebulawindphone at 7:50 AM on September 27, 2020 [10 favorites]

Best answer: Fizzing with CO2 is 100% normal for fermented vegetables. It's a good sign! Lactofermentation produces CO2; if it isn't allowed to vent it builds up in the jar and then fizzes out when produced.

Fizzing with CO2 is a bad sign for a sterile heat canned item. Canned vegetables are supposed to have literally no bacteria growing in them. If CO2 is present it suggests they weren't sterilized properly. The real danger with canning is that botulin bacteria survives a not-quite-completed sterilization process better than anything. And you can't easily detect botulism, and it really can kill you.

So the question is; were these fermented pickles or canned ones? My guess is probably fermented. If the jar doesn't have a sealed canning lid that's a big clue. If it's got a lot of salt in it that also suggests it was intended for fermentation (fermented are typically done in 2-5% salinity brine).
posted by Nelson at 7:57 AM on September 27, 2020 [8 favorites]

Best answer: It is absolutely normal for lacto-fermented pickles to produce carbon dioxide. That is precisely how the process works. Heterofermentative lactic acid bacteria consume sugar and produce lactic acid, as well as smaller amounts of ethanol and carbon dioxide.

So yes, this absolutely could be a normal result of the pickling process. And since, this was bought at a farm stand, I wouldn't expect much in the way of warning labels. I would absolutely try them myself, and if they didn't taste bad, continue to eat them with gusto. When live ferments go wrong, you usually know it immediately.

(Fermentation is pretty much the opposite of canning, so canning forums wouldn't be the best place for information here.)
posted by neroli at 7:57 AM on September 27, 2020 [5 favorites]

What nebulawindphone said! Well put. If it's fermented pickles then maybe read this description and see if it matches: UMN extension on making fermented pickles.
posted by Lady Li at 7:59 AM on September 27, 2020 [2 favorites]

Response by poster: This did not have any kind of label on it - it's just a clear glass screwtop jar. Sold to me by a really old guy at a stand at the edge of a field, probably made by some member of his family.

No venting holes or gaskets either, it does not look like it has been heat-treated. Also I am not in the US, home canning with a pressure vessel is very unusual here.
posted by each day we work at 8:04 AM on September 27, 2020

When you say it's a screwtop jar - is the lid in one piece, or two pieces?
posted by EmpressCallipygos at 8:06 AM on September 27, 2020

Response by poster: One piece, made of thin lightweight metal - shiny yellow on the outside, some kind of white coating on the inside.
posted by each day we work at 8:12 AM on September 27, 2020

Best answer: Given your description of the whole situation, I would guess that these are wild fermented (as opposed to inoculated with specific microbes) pickles and totally safe to eat. They're clearly alive (fizzing) so it's technically a risk...but one I would take with great enthusiasm. Your description of the fizzing and the liquid sounds exactly like the lactofermented everything I make regularly. A slimy film or obvious mold on the top of the exposed veggies, or a truly unpleasant odor (as opposed to the usual mild pickle funk) would be cause for concern, but your pickles sound delicious. Please eat them!

If you're worried, try a couple small pieces and see how you feel. The next day, assuming all is well, eat those pickles with abandon!
posted by JuliaIglesias at 8:24 AM on September 27, 2020 [8 favorites]

Yeah, my answer definitely assumed US canning styles and US norms about food safety. Sorry about that.

If it's a popular pickle style where you are, maybe you could around about whether it's usually made with salt brine or with vinegar? (Salt brine: fizzing is normal and good; vinegar: probably shouldn't fizz.)
posted by nebulawindphone at 12:58 PM on September 27, 2020

Um, I'd try to find the stand/farmer to ask. Otherwise, I wouldn't risk it. The odds of a problem may be low, but the consequences of a problem are very large, and the risk/benefit ratio doesn't appeal to me.
posted by amtho at 1:51 PM on September 27, 2020 [1 favorite]

probably fine. as stated above, lacto-fermented veg is often fizzy from CO2. i personally like a nice fizzy kimchi.
posted by dudemanlives at 4:17 PM on September 27, 2020 [2 favorites]

TLDR: confirmed cases of foodborne botulism in the US hovers around 30-40 cases per year in a nation of 300+ million
posted by dudemanlives at 4:24 PM on September 27, 2020 [1 favorite]

Response by poster: Pickle update: Tried one of the smaller tomatoes, it was briny and delicious.
posted by each day we work at 2:53 AM on September 29, 2020 [3 favorites]

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