So you bought an artisanal jar of pickles from a stand on the side of the road or, a while ago, pickled a few cukes yourself. You stored them—as you always should—in the root cellar, pantry, or a dark cupboard.
A few weeks in, you got the munchies. So you thought to give the pickles a try. Then this happened: on opening the jar, the lid popped, and bubbles began to appear for a couple of minutes, just like they do when opening a can of soda or hard seltzer.
Are fizzing pickles safe to eat, though? Can you eat them, or should you throw them in the bin?
The answer depends on whether the pickles were fermented or canned. While fizzing is normal for fermented pickles, in canned, heat-treated pickles, it is not. If a jar of canned pickles is fizzing, throw it away.
Unless stated otherwise by their producer, assume that store-bought pickles are canned and therefore should not pop or fizz when opened. If you made them yourself or bought them from a farmer’s market and you know for sure that they’re fermented, then popping and fizzing is most probably okay.
In any case, an off odor, funky taste, or excess mushiness of the pickles is a sign of spoilage. Fuzzy mold, green or blue, is another obvious sign that something’s gone really wrong in that jar of yours. Since spoiled food can be bad for you, the best thing to do when in doubt is to discard it and not to take the risk.
To understand why, you need to know the difference between fermenting foods and canning them.
What Are Fermented Pickles?
Fermentation is basically another way to say “bacterial breakdown of foods.”
When you ferment foods, you leave them at the mercy of friendly, non-harmful bacteria that feed on the sugars and starches contained in them, farting out carbon dioxide (CO2) as a byproduct.
This is called lactofermentation, and it imparts your cukes with a pleasantly sour taste and, as long as you keep them submerged in the salty brine, extends their shelf life to 4-9 months.
You make deli-style, half-sour fermented pickles by dipping them in a brine of water, salt, spices (mixed peppercorn, celery, coriander, fennel, and mustard seeds), fresh dill, and sliced onion, then letting them ferment for 3-4 weeks in a cool and dark place with a temperature of 70-75°F (lower temperatures require longer fermentation times).
“I remember getting pickles from a local store as a kid,” a member of a gardening forum says, “that kept them in a big barrel by their deli counter. I loved their half-sours and my sister loved their kosher dills, and mom a good ole sour pickle!”
At home, store fermented pickles in a canning jar or food container with a twist-top lid. These bacteria feed on carbohydrates and emit carbon dioxide in the form of gas bubbles. These gas bubbles accumulate in the container and you will need to open it occasionally to release them.
Unsurprisingly, when you open a container of fermented pickles, the lid will pop, and the brine will fizz. So fizzing from the buildup of carbon dioxide is normal—and expected—in fermented pickles.
The same, however, can’t be said for canned pickles.
What Are Canned Pickles?
Canning is when you jar cucumbers in an acidic brine and heat-treat the jar in boiling water. During the heating, the air gets driven out of the jar and, as the jar cools, a vacuum seal is formed.
The technical term for this is “sterilization.” You sterilize foods to destroy the microorganisms, which could otherwise induce food-borne illness, and inactivate the enzymes that could cause it to spoil.
To make canned pickles, you first need to make a pickling brine, usually with water, distilled white vinegar, pickling salt, and sugar that you bring to a boil. Then, you pack small and in-season cucumbers, along with bay leaves, dill stems, garlic cloves, and peppercorns, in jars, pouring the brine and leaving 1/2 an inch of space between the brine and lid.
Sealing the lids tightly, you submerge the cans in a canner or a big pot of water and bring to a boil, heat-treating the pickles for at least 15 minutes to kill the bacteria and inactivate the enzymes in them.
Last but not least, you leave them undisturbed for 24 hours before testing the seal on the jars:
Most store-bought pickles, especially those sold on shelves and not at the deli counter, are sterilized.
On a properly sterilized jar of pickles, the lid should never bulge. When opening the jar and breaking the seal, you shouldn’t hear a popping sound, nor should you see the brine fizzing.
If you just opened a jar of canned pickles (by “canned,” I mean heat-treated and therefore sterilized) and it started to fizz, that’s a tell-tale sign of bacterial growth. Throw them away immediately so that no one at home makes the mistake of eating them.
Fermented vs. Canned Pickles
Fermented pickles are cukes aged in salty brine and kept in a cool and dark place. A jar of fermented pickles contains living and breathing bacteria that feed on sugars and churn out gas bubbles.
Canned pickles are cukes jarred in an acidic brine and heat-treated to kill the bacteria, inactivate the enzymes, and form a vacuum seal on the package. As with all canned foods, the lids should never bulge or pop when opened, and the brine should never bubble or fizz.