Stages of Fermentation
Posted by Chris
The fermentation process is fascinating kitchen alchemy. Cucumbers become dill pickles and cabbage becomes sauerkraut, following a predictable step by step process. But we are the observers. The real heroes in this performance are the bacteria.
Looking at the transformation of cucumbers into pickles or cabbage into sauerkraut will give a better understanding of the stages of fermentation and what we can expect in our fermentation jars. This transformation involves three successive colonizations of helpful bacteria that are dependent on the acidity of the brine solution.
When you understand what these three colonizations are and what you will observe from each, you’ll be better able to gauge the progress of your ferments.
The Fermentation Process
The first 24 hours
In the first 24 hours, the brine solution inhibits the colonization of putrefying bacteria, allowing beneficial bacteria to colonize the jar. This beneficial bacterium is already on the outside of the cabbage leaves or cucumbers. You can favor the good bacteria by adding a few tablespoons of culture from a successful batch of fermented vegetables, or by adding whey. But the addition of an active culture is optional.
While we speak of “Lacto-bacteria,” as the catalyst for preserving vegetables by fermentation, in reality, the Lacto-bacteria require an acidic environment, which develops gradually during the fermentation process.
24 to 48 hours later
After 24 to 48 hours you will see fine bubbles forming on the sides of the jar. If you press gently on the glass weight with a clean knife, you’ll see bubbles rushing up to the surface. The pH drops within the brine as Coliform bacteria begins the fermentation process. The acidity is increasing inside the jar.
You can carefully push the weight down with the knife to release the trapped carbon dioxide bubbles, held under the weight. This will ensure that your vegetables remain in contact with the brine and that the fermentation process continues in the absence of oxygen.
After four days
After four days your fermentation will be active. You’ll notice gas bubbles forming in the brine. As the environment becomes more favorable, the Coliform bacteria drops off and the Leuconostoc bacteria begins to proliferate, further increasing the acidity of the brine.
The vegetables seem to be pushing the weight up in the shoulders of the jar. If the brine overflows through the fermentation lock because of the pressure, replenish the fluid levels with filtered water.
After six days
After six to 10 days, you’ll notice the bubbles inside the jar diminish. The conditions within the crock are acidic enough for Lactobacillus to proliferate, while the other bacteria drops off.
The fluid level seems to lessen, as the pressure from the ferment decreases. There may be a gap between the glass weight and the top of the vegetables in the brine. The active fermentation is completed but the sauerkraut or the pickles aren’t ready to eat yet.
The cabbage changes color from a bright green to a grey-ish, olive green. Cucumbers will change from a deep green to an olive green. The lactic acid reaches a high enough concentration inside the jar to preserve the vegetables.
However the ferment has not yet reached its best flavor. It will need a month or two inside your fridge before the Lactobacillus permeates the vegetables, souring it and causing it to become fully fragrant and sour-sweet like traditional sauerkraut or kosher dill pickles.
The fermentation process is predictable but dependent on temperature and humidity. If your ferment is progressing too quickly, you can slow it down by moving it to a cooler area. If it seems stagnant and reluctant to get going, move it to a warmer place.
But not too warm. Very high temperatures or exposing your ferments to direct sunlight can kill the beneficial bacteria and stop the process all together.
Now that you understand what happens on a microscopic level inside your jars you can have confidence that your fermentation projects are progressing as you hope.
Sandor Katz. The Art of Fermentation: An In-Depth Exploration of Essential Concepts and Processes from around the World (Chelsea Green Publishing, 2012).