pickled cucumbers seemingly lasting "forever"

My girlfriend's grandma has made pickled cucumbers for decades and distributed them to her whole family.

They are delicious, despite the jars looking like swamp water.

On one occasion, we got her some new jars and she later said that the older jars were better because they are not as tight as the new ones. Apparently they produce some gas and need to vent and I noticed that the sides of the jars show some dried liquid, so it is clear they all leak somewhat.

So, I'm wondering how can food which is not airtight and not refrigerated can last for months without spoiling? She's been doing that for 50+ years so somehow the technique works, but I'm curious about it.

Edit:

Today I had the opportunity to question grandma about her method :)

She's 85 so she just knows what's she's always done :) the pickling is not using any heat, it's cucumbers, vinegar, salt, tons of spices and herbs. she puts everything in jars that will 'gas out' and leak for a few days, and then after that another process seems to take place where the jar seals itself, doesn't leak anymore and becomes harder to open, so I guess the air inside is somehow consumed.

food-safety pickling

Best Answer

I have to admit I am speculating a bit here. Your pickles are fermented, which itself is a form of preservation. The type of fermentation taking place is likely acetic, since the added vinegar could work as a starter, but it's also possible that you have a lacto component. It depends on the proportions of salt and vinegar used.

That said, as whatever bacteria and natural yeast get to work, they convert sugars naturally present in your vegetables to various acids, alcohol, and carbon dioxide. The production of carbon dioxide will indeed cause an increase in pressure and make a sealed jar leak.

As the fermentation settles down what will often happen is the lid will glue itself shut with a combination of partially digested sugars and salt that dry out. This doesn't really indicate negative pressure, but can make a jar a major pain to open.

As for how it works - the short version is comprised of two parts. Part one is that the good bacteria and yeast go through and eat everything, making it harder for bad bacteria to get a foothold. Part 2 is that as a result of the fermentation, the brine in the pickle jar is very acidic (not to mention salted) and therefore very unfriendly to most bacteria even if there was sugar to be had.

That's an extremely simplified version, obviously. But fermentation has a long, long history as food preservation. It's an absolute classic from a cultural perspective, and is biologically complex. I would make sure that grandma's recipe is written down (if you can), since it can be dangerous to fool around with an untested fermentation procedure. (I personally consider 50+ years to be "tested" enough...)