The three stages of sauerkraut fermentation
In order for sauerkraut to be a success, it must go through three specific stages of fermentation.
Stage One
Leuconostoc mesenteroides initiates sauerkraut fermentation. Since Leuconostoc mesenteroides produce carbon dioxide, it effectively replaces the oxygen in the jar, making the environment anaerobic (oxygen-free). When lactic acids reach between .25 and .3%, Leuconostoc mesenteroides bacteria slow down and die off, although enzymes continue to function.
This stage lasts between one and three days, depending on temperature.
Stage Two
Lactobacillus plantarum and Lactobacillus cucumeris continue the ferment until lactic acid level of 1.5-2% is attained.
High salt and low temp inhibit these bacteria, so I hope you didn’t over-salt your cabbage – and be sure not to refrigerate yet.
This stage continues for 10-30 days, depending on temperature.
Stage Three
Lactobacillus brevis (some sources also include Lactobacillus pentoaceticus) finish off the ferment. When lactic acid reaches 2-2.5%, they reach their max growth and the ferment is over.
This final stage lasts under a week.
You will know your sauerkraut is ready for long-term storage (or to eat!), when no more bubbles appear on the sides or top of your jar.
There is a nice image of the stages here.
What can affect the way my sauerkraut turns out?
Although the process is simple, and will complete well on it’s own with the right amount of salt added, there are some factors that do influence how sauerkraut will turn out. These are: moisture, oxygen concentration, temperature, nutrients, and pH. Let’s address these one at a time:
Moisture
Bacteria that love to spoil sauerkraut will have the upper hand if you have an insufficient level of brine. Too low a water/brine level and you’re giving the undesirable aerobic (oxygen-loving) bacteria and yeasts the food they need to grow on the surface. This can cause off-flavors and discoloration at minimum, or even an allergic reaction to those with sensitivities to mold and yeast.
Although white yeast “scum” on the surface can be scraped off without harm to you, mold is another story and will be addressed further in another section. Briefly, one way to eliminate the mold problem (because you certainly can’t drain the moisture out of your ‘kraut) is to make sure oxygen exposure is kept to an absolute minimum since molds need oxygen to survive. Which brings me to…
Oxygen Concentration
Lactobacillus plantarum, the primary bacteria responsible for Stage Two, works best without oxygen. Anaerobically (without oxygen), Lactobacillus plantarum does their job the way we want them to – they cause fermentation of cabbage via lactic acid. Aerobically (with oxygen), it will produce acetic acid (vinegar). Since we’re making sauerkraut, oxygen must be avoided.
Sauerkraut that is allowed oxygen will not contain any vitamin C in the final product after just six days. It will also increase chances of mold forming. If you are regularly getting mold on the top of your cabbage, this is a visible sign you are allowing too much oxygen in. Oxygen also allows pink yeasts to grow and could result in soft ‘kraut.
Finally, don’t mess with your brine. When brine is stirred, you introduce air which make conditions more favorable for growth of spoilage bacteria.
Temperature
Micro-organisms are classified into three categories according to their temperature preferences. Since sauerkraut falls into the mesophilic category, the bacteria involved prefer a minimum of 50-77° F; an optimum of 86-104° F, and a maximum of 95-112°F. These are the temps that all bacteria prefer (non-pathogenic as well as pathogenic).
In the first stage of fermentation as described above, the Leuconostoc mesenteroides from stage one likes a temperature range of 65-72° F. It’s a little flexible, and built to resist some change in temp.
The second- and third-stage bacteria Lactobacillus plantarum, Lactobacillus cucumeris, Lactobacillus pentoaceticus, and Lactobacillus brevis prefer a temp of 72° F – 90° F.
It’s important to keep these temps in mind, to be sure you provide the right environment for these bacteria to grow.
Temperature also affects enzymes, which are destroyed once the temperature has risen to 115 degrees.
Nutrients
Nutrients also affect the outcome of sauerkraut, salt being the primary nutrient of concern.
Salt should be added at a ratio of about 2-3%. Much more than this andthe Lactobacilli can’t thrive. A good rule of thumb is one tablespoon of salt per two pounds of cabbage.
Be sure to add salt as evenly as possible – if you create pockets of cabbage that aren’t salted, you are sending an open invitation for spoilage bacteria to invade and turn your cabbage brown, or for yeasts to turn it pink.
It is essential to use pure sea salt. Salts with added alkali may neutralize the acid, resulting in a failed sauerkraut.
pH
pH is a measure of hydrogen ion concentration. Foods with a pH above 4