My water disappeared

[Christopher Weeks]

If bacteria are converting solids to gasses (as they do when giving off CO2), the volume of the gas should be tremendously greater than the volume of the solid. So the over-time pressure differential should always be greater pressure on the inside.

I think the inflow almost has to be caused by substantial short-term temperature fluctuation. (Like the overnight temperature drop proposed by Rich.)

[Gutted]

If bacteria are converting solids to gasses (as they do when giving off CO2), the volume of the gas should be tremendously greater than the volume of the solid. So the over-time pressure differential should always be greater pressure on the inside.

I think the inflow almost has to be caused by substantial short-term temperature fluctuation. (Like the overnight temperature drop proposed by Rich.)

You might think that but many people have noticed suction when using crocks and this seems to be a constant phenomena after a ferment is started rather than being when temperature changes. Temperature might make the matter worse but I do not think that temperature is the sole causational factor in this problem.

My fermentation crocks lids are always tightly fixed, sucking the lid down which makes me wonder why CO2 needs to escape if the pressure always seems negative. Why does the CO2 not cause the pressure to reduce like it theoretically should?

It does need closer testing to make sure that there is negative pressure inside but from my experience there does seem to be negative pressure. I have not noticed the lid to be easy to lift.

The CO2 produced should counter act the reduction in volume but it does not seem to do that. Can temperature have a larger effect on the internal pressure than we think?

Maybe some science on CO2 and temperature would help.

Also a previous poster did mention that he had very tight temperature control so he should not be having the problem and yet it does look like he does get it.

[Christopher Weeks]

I don't have a water-lock crock, but I sort of wish I did, just to play with it.

I'd be interested, if someone who has one empty was willing to fill the moat of a lidded empty crock and then hit the bottom of it with a hair dryer and report back how much bubbling and how responsive it seemed to be.

The Ideal Gas Law tells us that if the amount of gas is constant (which we can't count on, in fermentation, but it has to be pretty close over short periods of time), then pressure times volume = temperature. So when the gas inside the crock cools, PV decreases as the gas contracts, drawing water in the moat toward the inside. If it cools enough, either water enters the crock proper or bubbles from outside transit through the water and into the crock. The latter is what I assumed would happen, but I suppose it depends on how full the moat is..?

We know for sure that normal lacto-fermentation (and also fungi eating sugar) gives off CO2. And in my experiences with lots of veggies, but no moat-style crocks, when I have sealed jar, pressure always builds up over time and negative pressure never happens. But, y'know, there's lots of room for not knowing stuff.

Maybe one of the processes that our microorganisms engage in is fixing atmospheric gasses into solids in the brine. They might well do that some during reproduction, for instance. As the mass of the colony increases, that matter has to come from somewhere. It could be coming from your produce, but it could also be from the gasses above the brine. Maybe some bugs do that more than others. Or maybe, during some stages of fermentation pipeline, that happens more than during others.

[JohnDulleck]

I tried a google search for air locks being sucked back into the ferment during lacto-fermentation, but only got results for beer or wine, and the air locks in question were the plastic ones that go on top of a jug or carboy.

But then I got to thinking about how all of the water could get sucked out of a crock with a moat, and I really don't see how that could happen, at least not if the crock construction is anything close to reasonable.

Now, I don't have such a crock,so I will make a couple of what I think are reasonable assumptions.

First, I assume that the moat walls are approximately the same height on both the inside and the outside. Now, if the moat, with the lid is in place, is less than half full, then it would be impossible to overflow the moat, even if the lid had no vent holes. But the vent holes give an extra level of protection against overflowing the moat when CO2 is being vented. As soon as the moat level inside is forced lower by pressure, CO2 will bubble through the vent holes in the lid and the levels inside and outside the lid will equalize, more or less.

As far as liquids and gasses are concerned, there is no such thing as pressurization or vacuum, there is only difference in pressure. If the pressure difference inside the crock is positive, then CO2 will be forced out. If the difference is negative, then air will be sucked in. But in either case, the water level cannot change beyond what is dictated by the vent holes in the lid.

Therefore, I think the chance of water being sucked into the crock to the point where the moat is dry is either slim or none, in my opinion. In my opinion the explanation lies elsewhere.

[Tibor]

On my 7.5 L Gartopf crock ,the inner height of the moat is a half inch taller than the outer edge. There are 2 notches in the lid so when it needs water it's all equalized right away. I don't recall ever having liquid sucked into the crock.

[Gutted]

Water in a crock reservoir will tend to evaporate and reduce. However oil in a reservoir will not! If oil is sucked back into the crock it is clearly visible floating on the water inside the crock, which the last time I opened a crock ferment the oil WAS floating on the water and was a total nightmare to remove. Something I will never do again because I will just dump the whole lot straight in the bin rather than spend the hours it took me to remove it the last time.

If you are sure that it does not happen then I suggest you use oil and find out for yourself. There is no mistake with oil because it can clearly be seen.

I bet this is far more common than crock users are aware, it's just that when using water in the reservoir you do not realise that the water is being drawn back into the crock. Topping up the reservoir thinking it has evaporated when it is actually being sucked back into the crock. Trying to lift up the lid a bit at different times after topping up the reservoir should show if there is any suction present. If the lid is tightly held down then there is suction present and anything in the reservoir will be drawn back into the crock. That is a bit of a giveaway IMO .

I am extremely disappointed with fermentation crocks and will not use them unless I find a solution sometime in the future. I have no time to waste ATM because I have much more important issues to deal with.

[Dgocowboy]

That has happened to me with my crock, and as best as I can figure out it was a barometric pressure change creating low pressure inside the crock (hence the vacuum feeling when you try to move the crock). Since nature abhors a vacuum, it sucks in what it can and drains the gutter as it tries to equalize pressure. Your ferment should be fine if you just keep adding water (or brine) to it.