# What strength of brine will completely inhibit growth of lactobacillus (and friends)?

As per the title. How strong does a brine have to be before it will completely inhibit growth of the bacteria that are traditionally employed to create pickled foods?

The backstory is that I decided to make some sauerkraut the other day. The recipe I looked at said to use a 3.5% w/w brine. I filled the jars with the sliced cabbage I had to see how much they would take, and the cabbage I had filled two jars. So I measured the volume of the jars, remove the cabbage into a large bowl and added the correct amount of salt for a 3.5% brine that completely filled both jars. However after an hour of contact with the salt, the cabbage had wilted enough that all of it fit in one jar, leaving me with effectively a 7% brine after adding enough water to cover the cabbage. It's been two days since I left the jars covered with some muslin to ferment, however they don't smell particularly lactic. I'm partly worried that I may have added too much salt and thus inhibited the growth of the lactobacillus, but I'm aware that fermentation can take time, especially in cold conditions.

Mostly I'm just curious for future reference as to how strong a brine is too strong to stop lacto-fermentation.

• I have just fermented vegetables using brine, from the guidance in the "Noma Guide to Fermentation" book. In that, they take the weight of plain water AND the vegetables, and calculate 2% salt by weight, which is effectively saying the veg are 100% water by weight. So basically fill your jar with the veg, cover with the plain water, weigh the whole thing. Subtract weight of the empty jar, work out 2% of that by weight, for salt. Pour the water out of the jar, completely dissolve the salt, return it to the veg jar, close, and agitate to mix completely and remove bubbles. Hope that is of help ! May 30, 2019 at 13:07

In brief, your question has no possible general answer for the kind of scenario you posit (where you add a certain amount of salt to a certain volume of food) or even a scenario where you add a brine of concentration X to a certain amount of food.

Most vegetable (and animal) sources for food contain significant amounts of water, and some of that water will be released when placed into a brine solution. The amount of water that is released will alter the final brine concentration, often significantly. Reputable recipes for food preservation and brining will take into account the average amount of water released to arrive at a final brine concentration that will ensure food safety (while not making the food unpalatable and perhaps allowing bacteria to grow if fermentation is desired). The safety of such recipes is generally determined empirically through extensive testing to ensure the final products are stable. There's no general formula you can use.

Now, if you actually have a way of determining the final brine concentration after the food has released all of its water, you can answer your question for various bacteria strains. This paper has a summary of minimum levels of water activity (in Table 5) that will allow bacteria to grow. For Lactobacillus, using Table 4 in the paper, you can see that the maximum salt concentration which will allow growth could be anywhere from 7% to 16.5%, depending on the particular strain of Lactobacillus.

However, note that these are absolute maximum salt concentrations that can allow any growth. At high concentrations, the activity of Lactobacillus and other fermentation bacteria will slow significantly. By the time you get above a 10% solution or so, you're going to see very slow fermentation, and it is possible that other bacteria, yeast, and mold that can survive such high salt concentrations might grow first. (Lactic acid fermentation works by using both salt and resulting acidity as preservatives; if the lactic acid bacteria cannot grow fast enough, the lower acidity may allow other bad things to grow.)