I don't know, but it sure does look like the bacterial debris that sinks to the bottom of a naturally fermented pickle. Tell us about the recipe.

I had a lot of raw unripe cherry tomatoes that I rinsed well in hot
water and packed into jars. These were the last of the few trays of baby
greens. I had already had a long day of canning pints of them too.
Super cute, eaten too soon :)
Brought to a boil a 50/50 ratio of white vinegar if I am recalling right, plus two tablespoons caning salt.
Put seasonings into bottom jar. Whole mustard seed, pepper flake,
coriander, fennel seed. Then warm washed tomatoes. Then boiling brine.

Then I loose capped them and left them out on the front porch in the
cooling cabinet for a few hours since it was extra cold that day.
Hovering around freezing.

Then tossed the jars into the back of my fridge before went to bed that night and forgot about them.

Lol.. This was around mid October last year. So they have been in the back of the fridge for a while.

So they were never processed? Never vacuum sealed? Then the air left in the jars would allow for bacterial, mold, or fungus growth. Most pickled green tomato recipes call for almost straight vinegar and for the seasons and tomatoes to be heated in the brine as well. Especially if they aren't going to be processed.

Dave

I've never canned fridge pickles? Thought that was part of the point was that you don't do the canning.

But anywho, I dug through my notes. I was processing so much at that time, heh. Turns out this was the lacto-fermented batch, not a straight up fridge pickle batch. So the previous note about how I processed them is wrong, that was a different something, lol.

So what I did was at the end of the canning night- I water bath pickled a few jars of green cherry tomatoes, and was pretty wiped out to do another batch.I brought the jars up to a brief boil while I prepped up the tomatoes.

Pulled jars out of hot water,. into each jar went 2t mustard seed, 1t peppercorns, 1t dill seed , 1/2t hot pepper flake, 1 bay leaf, and a couple small whole fresh garlic cloves.

Brine was 10 cups water, and 50 grams of salt, I used 30 grams of canning salt, and 20 grams of large flake sea salt. Brought briefly up to a boil and salt added in, then cooled down to room temp before pouring over the tomatoes.

Weights went into the top of the jars, then the jars got capped with clean coffee filters bonnets. Sat on the counter for 4 days or so till they stopped bubbling. Then they got their solid cap and ring, and went into the back of the fridge. This was in October.

Only four days of fermenting sure sounds short. But from the looks of the jar, they must have continued some fermenting even in the fridge. When I fermented green tomatoes they never had visible bubbles in the brine, so maybe yours fermented faster than mine. Did you smell these when you made the photos?