Lacto-fermentation: An upgrade and an experiment

In my last post about lacto-fermentation, I mentioned an improved method for keeping carbon dioxide on top of the vegetables. Here's the blog post where I read about it. Just like wine fermentation, an airlock is used to allow carbon dioxide to escape (pushing the air out ahead of it) without letting oxygen in.

I bought a couple more airlocks (I have a dozen or so, but they're all in use) for 50p each from the health food shop where I buy my home brew stuff then went to the hardware shop in search of rubber seals. I wandered around the shop looking at various bits of rubber that weren't quite what I wanted, but might do, then approached the lady at the counter. I presented an airlock and explained, I'm looking for something that'll seal that into a jar lid. A rubber grommet would be ideal... I don't suppose you have anything suitable? She reached behind her and took a small box marked Grommets from the shelf, and tried several until she was sure she had the right size, then sold them to me for 15p each. I bought four.

With a bit of trial and error, I found the best way of gripping a jar lid for drilling. Trying to grip the edge doesn't work very well, as the edge slips easily if gripped loosely and the lid is flimsy and bends if you grip it more tightly. However, a lid is designed to grip to something - the jar itself - and the jar can be gripped more easily.

I drilled a pilot hole first, then used the flat drill bit to make the correct sized hole.

It wasn't easy getting the grommets into the holes as I'd drilled the holes to be a very tight fit, and also smeared Vaseline into the groove to stop the cut lid going rusty. I did manage to get them in without too much swearing, though, and then the air lock fitted in quite easily.

My next two vegetables for lacto-fermentation - samphire and sloes, of which more in a future post - both had a much higher salt content than the courgettes and beans I'd started with. They both showed signs of fermentation but very, very slowly. I suspected that the bacteria were not thriving in this very salty environment. I decided that the next time I had a suitable opportunity, I'd compare different levels of salt to see whether it made a difference to the speed of fermentation.

The opportunity presented itself when a neighbour gave me a couple of marrows (the same neighbour who'd given me courgettes earlier in the year - he now has a great many marrows). I modified the lids of a couple of large jars that a friend had given me (thanks, Steve!) to make two similar fermenting vessels.

To keep the two jars as similar as possible apart from the salt content, I filled them at the same time: From the heap of marrow pieces, one handful in this jar, one handful in that jar. After each layer of marrow, I sprinkled in salt: One pinch per layer in one jar, three pinches per layer in the other jar. This is still quite a lot less salty than the samphire and sloes, but I don't want my marrows that salty. Comparing three pinches with one pinch should give a clear difference in salt content, even allowing for variations in pinch size (which shouldn't be systematic, in any case). I pressed down the veg as I went and plenty of water was drawn out, so I didn't need to add any to either jar. Instead of blackcurrant leaves, I inoculated the jars with liquid from the fermented courgettes to get the right bacteria in there*.

Two jars of marrow pieces, matched (reasonably) carefully on everything except salt content

I had imagined these air locks bubbling as they do with wine, so that I'd be able to count bubbles per minute or some equivalent. Unfortunately it didn't quite happen like that. The bubbles certainly formed in the jars but with the jars so packed full of marrow, they couldn't rise to the top so they just stayed there. Eventually, of course, enough pressure built up that something had to give. What gave was not gas but liquid, which got a little messy.

More salt is currently in the lead

At this stage the 'three pinch' jar was looking distinctly more active than the lower salt jar. I started to worry that I hadn't matched them adequately and had overfilled the 'three pinch' jar, which was why it was overflowing. Although I was reluctant to break the air locks, I opened both jars to push the veg down. There was no sign that I'd overfilled the higher salt jar; in fact, having overflowed, it now had less liquid than the other one. I spooned a little liquid out of the 'one pinch' jar to compensate, and resealed the lids.

After that nothing much happened for a few days because the temperature's quite a bit cooler than it was in the summer. I put both jars on top of the cooker for a bit to encourage some action and again, it was the 'three pinch' jar that lifted its cap. Things continued in this vein for a couple more weeks, until I decided that it must be time to open the jars and taste the results of my experiment. At this point another difference became apparent.

More salt still winning

I had noticed some mould forming at the top of the jars (or is it yeast? Either way, it doesn't smell very nice), and it's not very surprising that there's more in the lower-salt jar. I scooped out all of the mouldy marrow pieces (rather more from the lower-salt jar) and tasted the fermented marrow. Both jars tasted OK - the only difference was that the more-salt one was... saltier. A bit too salty for my taste, actually, so I'm glad I didn't try a higher concentration of salt for the experiment - I would have ended up with a whole jar full that I didn't want to eat. I couldn't detect any difference in acidity, which surprised me, given the apparent differences in fermentation activity, but perhaps I just couldn't tell over the saltiness.

The presence of mould indicates that the upgrade wasn't entirely successful. That space at the top was supposed to fill up with carbon dioxide so the mould wouldn't grow there (unless of course it's yeast, which can grow anaerobically, in which case pushing out the oxygen wouldn't help). The fact that the bubbles were getting stuck was a sign that things weren't going entirely to plan. I wonder if I need a little more liquid per vegetable solid, or maybe I just need to cut the pieces smaller so it's easier for the bubbles to find a way through. Either way, I don't want a stack of solid pieces that trap the bubbles when they form. Probably.

Conclusion: Three pinches of salt per layer appear to provide a better environment for fermentation than one pinch per layer, though there was no obvious difference in flavour apart from the salt itself, which favoured the less-salt jar.

You'll notice that I don't generalise to 'more salt is better for fermentation' which you might think is a cop-out just because the results didn't go the way I predicted, but there is a reason: From some reading I did at the same time as running this experiment, I learnt that whilst salt is generally bad for bacteria (which is why salting is an effective method of preserving food) lacto-bacili are more resistant to salt than most. The reason for adding salt here is to kill off the bacteria that we don't want, leaving no competition for the ones we do want. If we add too much salt we'll kill off our friendly bacteria as well.

There is an optimum level of salt and it appears to be closer to three pinches per layer than one pinch per layer of marrow. It's still possible that my samphire and sloes had too much salt, but this experiment didn't really address that question because I didn't include such high levels of salt. You could legitimately say that this is a weakness of my experimental design.

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* Some people believe that this method gives an inferior result, as what you really want is the progression of microbes that occur naturally, to give the full complexity of flavour, not just the one that comes in at the end and makes the acid. Others say it's hard to tell the difference. I don't think I'm that fussy, at least not at this stage.