Like a fine wine, sauerkraut improves with age, not only in flavor but also in the population of good bacteria. Beneficial lactic acid bacteria (LAB) multiple into the TRILLIONS as a jar of sauerkraut is fermenting! Some sources say 10 trillion bacteria in one serving size of fermented sauerkraut.
Fermentation happens in stages and takes time depending upon the vegetables you’re fermenting and ambient room temperature.
To obtain the greatest health benefits from eating probiotic-rich sauerkraut, you’ll want to let your sauerkraut or vegetables ferment long enough to go through the three stages of fermentation at the end of which the population of various types of LAB reach their peak levels.
Let’s first cover the three stages of fermentation, followed by a few factors that impact how long it takes for these stages to unfold.
- Fermentation Stages
- Salt Concentration, Temperature, and Vegetable Quality
- How Long to Ferment?
Stage One: Days 1-5, approx.
The first stage of fermentation starts from the moment you mix salt into your sliced cabbage and prepared vegetables.
Surprisingly, the levels of LAB are at extremely low levels in the starting ingredients—sliced cabbage, specific vegetables used in any particular batch, salt and seasonings, which may suggest that only trace amounts of LAB are necessary to initiate fermentation.
In this first stage of fermentation, the L. mesenteroides—the most common organisms associated with vegetables—do most of their work. They are the smallest of the three bacteria studied and are able to tolerate salty conditions.
They break down available sugars to produce lactic acid, acetic acid (vinegar), ethyl alcohol, and mannitol which all contribute to the characteristic flavor of high-quality sauerkraut. If the fermentation temperature is higher than 72° Fahrenheit (22° Celsius) they might not grow, which would be detrimental to the flavor of sauerkraut.
The L. mesenteroides also produce carbon dioxide (soda gas), hence the bubbles you see floating to the surface along with brine being pushed out of the jar. The carbon dioxide displaces any oxygen in the jar—or brine—to help create an anaerobic fermentation environment.
Once all the oxygen is used up, stage two begins.
Stage Two: Days 5 to 7, approx.
The L. plantarum does most of the work for the longest time period, from day 3 to day 16. Its only job is to eat sugar and produce lactic acid. The lactic acid that acts as a preservative, supports digestion, inhibits growth of harmful bacteria, increases the bio-availability of Vitamin C, among other jobs. Ideally, you don’t want to stop the work of the lactic acid bacteria by putting your sauerkraut into cold storage before day 16.
The L. pentoaceticus “finish-off” the sauerkraut during days 16-20 by lowering the acid level a slight bit more.
So, make it your goal to ferment for the full 3 weeks if your fermentation temperature is in the ideal range of 65-72° Fahrenheit (18–22° Celsius).
When I teach my workshops, I have people open their sauerkraut on day 7 and taste. If they like it, put it in the fridge. Then, with the next batch they make, ferment it for two weeks. Taste and evaluate. If it is too salty, there is not enough tang or if it is too crunchy, let it ferment longer and try it in another week. Work with it until you find a taste and texture everyone is happy with.
The best quality sauerkraut is fermented for a minimum of 20 days. This time span ensures good flavor development, proper acidity level, and complete consumption of all the sugars in the cabbage.
Salt Concentration, Temperature, and Vegetable Quality
There are four variables you can play with that impact the taste, texture, and tang of your sauerkraut:
- Salt Concentration
- Vegetable Quality
I like to keep coming back to these factors when tasting my sauerkraut. Some like it salty, some like it soft, some like it crunchy. And, some want as many beneficial bacteria swarming around in their jar as possible.
Salinity (Amount of Salt Used)
1 Tablespoon (15 ml) Salt for 1 ¾ Pound (28 ounces, 800 grams) Vegetables
The amount of salt you mix with your cabbage and vegetables determines the salinity of the fermentation environment. The best quality sauerkraut is made with 2-2.5% salt. This calls for mixing
1 tablespoon of salt (or 16 grams if weighing your salt) with 1 ¾’s pounds (28 ounces, 800 grams) cabbage and vegetables, or
3 tablespoons of salt (or 48 grams if weighing your salt) for 5 pounds (2400 grams, 2.4 kilograms) of cabbage and vegetables.
Too little salt speeds up the fermentation and might produce soft or slimy kraut. Adding too much salt slows down the fermentation and will inhibit the growth of the lactic acid bacteria, just the bacteria you want.
More on salt:
Ideal 65-72 Degrees Fahrenheit (18–22 Degrees Celsius)
The best quality sauerkraut is produced at a temperature range of 65-72° Fahrenheit (18–22° Celsius) without more than a 5° Fahrenheit (3° Celsius) swing in temperature. If your house is warmer than this, try fermenting for a shorter time period. If your house is cooler, then you will need to ferment for a longer time period.
Do find a place to ferment that is below 75° Fahrenheit (24° Celsius). This may require testing out different spots in your home or not fermenting during the warmer summer months. Traditionally, sauerkraut is made in the fall when temperatures are lower. In Korea, pots are buried in the ground in the fall to ensure ideal fermentation temperatures in their warmer climate.
If you have great temperature swings in your house – maybe it’s winter and you’re heating your house with a wood store – then you are continually stopping and starting the process and may end up with mushy kraut and need to look for a more stable environment.
65° Fahrenheit (18° Celsius), has the best flavor and color and higher vitamin C levels.
60° Fahrenheit (16° Celsius), the curing may take 6 to 8 weeks.
70 to 75° Fahrenheit (21-24° Celsius), however, also has good flavor and is ready in only a week or two.
Above 90° Fahrenheit (32° Celsius), the kraut will ferment in just seven to ten days, but most of the work will be done by homofermentative bacteria, which produce lactic acid but not acetic acid and other flavors which contribute to the complex flavor of really good sauerkraut.
The Best Quality, Ideally Local and In Season
Cabbage and vegetables of the highest quality will produce the best sauerkraut. More on vegetables to use for sauerkraut here.
Remember, you are feeding the bacteria that live on the cabbage. Feed them well with high-quality, ideally locally grown vegetables.
In addition, the sweeter the cabbage the higher the final quality of the sauerkraut. Remember, the lactic-acid bacteria eat the sugars (carbohydrates) in the cabbage. The sweeter it is, the more they have to eat.
Learn more about how to choose the best cabbage for sauerkraut.
Play with it! Have fun! Realize that every batch will be different. As much as we want to control the fermentation process, really we can’t. But, go back to salinity, temperature, time and vegetable quality when evaluating your sauerkraut.
And remember, your sauerkraut will continue to ferment in your refrigerator, though at a much slower rate. So, if you feel uncomfortable leaving it on your counter to ferment for 3-4 weeks, then move it to your refrigeration and forget about it for a few months. The flavor will have evolved and developed at a deeper level.
All these nitty-gritty details are covered in my photo-rich easy-peasy recipe. Check it out, you’ll be pleasantly surprised!
How Long to Ferment?
Safety. Taste. Bacteria.
So, just how long should you ferment your sauerkraut? For starters, until you like the taste, texture, and tang of your sauerkraut! After all, you have to like it to eat it.
Many have a hard time waiting for three weeks with their first few jars of sauerkraut. Plus, it is rather unnerving to leave a jar of food just sitting on your counter. As you feel more comfortable inviting trillions of critters from the microbial world into your kitchen, you will be able to let it ferment for a longer time period.
That being said, the minimum length, that I recommend, to ferment sauerkraut in your jar on top of the counter is one week. This gives it time to establish some beneficial bacteria, create lots of brine (which peaks around day four) and also prevents disturbing the nice anaerobic environment you’ve established.
The purists out there will tell you the minimum time to ferment is three weeks and that is what I aim for. This three-week time period gives an opportunity for a wider spectrum of beneficial bacteria to establish themselves. Some strains of bacteria populate that jar of yours at one week and others peak at the three-week mark.
I take care of all these details for you in my photo-rich recipe. Click below to try it out – it’s free – and you’ll be on your way to making probiotic-rich sauerkraut!
Now let’s look more closely at three factors that impact fermentation and can play a factor in how long any particular batch should ferment.