The Science of Sauerkraut

Sauerkraut-wikipediaFermented foods are often promoted as a good way to get beneficial bacteria into your digestive tract if you have bowel problems like ulcerative colitis, Crohn’s disease or IBS, or one of the many other conditions that come bundled with free bowel dysfunction, such as ME/CFS. And it’s true; gross-tasting fermented food can provide you with much needed friendly bacteria. But it is not a panacea.

The reality is that only certain bacteria are produced in the making of sauerkraut and other fermented foods. If you already have these in your gut and are lacking something else, then sauerkraut isn’t going to fix your problems. You might have endured eating it for no good reason!

So it might be worth a go, but if you want to be really scientific about it then you can first find out what bacteria are in your gut with a test through a company like uBiome or AmericanGut and compare your results to see whether the types of bacteria present in sauerkraut are already present in your gut, or not. You may find there is no need and thus avoid the misery of eating this rank ‘food’.

How does the fermentation process work?
There are a bunch of factors that influence which bacteria are in your sauerkraut, pH, length of fermentation, temperature, salinity, etc. and there is a large turnover of different types of bacteria as the fermentation progresses with the dominant species changing as the fermentation environment becomes more acidic.

What happens is that lactic acid bacteria (LABs) metabolise the glucose and fructose within the cabbage and produce lactic acid, and to a lesser degree acetic acid and mannitol, as by-products. Lactic acid overtakes glucose in concentration after just 7 days of fermentation. As the environment changes, so do the species of bacteria that are more suited to the conditions present.

As the name suggests, LABs are a group of related bacteria that all produce lactic acid, and the production of this acid helps to inhibits pathogenic bacteria and other organisms that might cause spoilage. LABs are generally considered to be safe, and occur in many foods such as cheese, beer and wine. They are present in healthy guts and often absent in autoimmune conditions. They belong to the Order Lactobacillales and if I look at my uBiome results, it seems that mine are much lower than average:


And this is not explained by my having been on long-term antibiotics. Many Lactobacillales are antibiotic resistant [2] and looking at my result compared to the antibiotic comparison group, the normal range is actually a lot higher than other groups, as high as 14.3% (because other types of bacteria are killed while Lactobacillales survived) which is double that of healthy omnivores. Mine are probably low for some other reason; either because of disease, or due to some other unknown factor. Increasing my lacrobacillales is unlikely to cure me of anything, but it may help a bit.

Exactly which bacteria are in the sauerkraut?
There are some limitations to the studies that have tried to answer this question. As fermentation progresses and the environment becomes more acidic, some bacteria that are present at the start of the process may be dead by the end. Some test methods would identify both the living and dead types without being able to say which ones were alive at the end. Other test methods get around this by culturing living bacteria though this also has limitations as some types of bacteria do not culture well.

That said, A 2007 study by Plengvidhya et al [1] looked at cultured isolates and also 16S rRNA gene sequence analysis in commercial samples and reported a rapid increase in the numbers of LABs and a rapid decrease in populations of Enterobacteriaceae in the first week of fermentation.

They conclude that “Under normal conditions, the fermentation is essentially complete within 2 weeks, with the most-acid-tolerant species, Lactobacillus. plantarum, predominating.”

L. plantarum was by far the dominant species, making up between 80% and 100% of the population after 14 days in different samples. Sadly, a small population of bacteria, less than 10%, was classified as “Unknown” at 14 days, followed by relatively small populations of Lactobacillus. brevis and Lactobacillus. paraplantarum.

Before this, at 7 and 9 days you also see these other LABs present that do not survive to 14 days:
Leuconostoc argentinum, Lactobacillus curvatus, Lactobacillus coryniformis, Leuconostoc fallax, Pediococcus pentosaceus. I suppose, if you felt that having these present in your gut were a good thing, then you could consume your sauerkraut at this earlier point.

Leuconostoc mesenteroides, Weissella species and Leuconostoc citreum are present earlier in the process in the first few days and are key for kicking off the fermentation process.

How much bacteria is present? I could just take some pills which taste a lot nicer…
It varies over the course of the fermentation but we are talking about billions of colony forming units per gram. L. plantarum and L. brevis have been well studied and have shown a wide variety of health benefits. You can buy some of the above as pro-biotics, if you prefer.

Fine, I want some of this nasty stuff. How do I make it?

fermenting crock pot

fermenting crock pot

Commercially it is made in big tanks, or in wooden barrels, and you can buy some and save yourself all the effort if you like. Just make sure you buy unpasteurized sauerkraut, or else it’s just sauerkraut with dead bacteria, and unless you like the way it tastes (hardly likely) then there’s little point eating it.

At home, it is typically made one of two ways: in a fermenting crock, or in a sealed jar. In either case, one of the main things you’re trying to do is remove all the oxygen from the equation. Lactic acid bacteria do not need it and many pathogenic bacteria do. I have not tried making it in a jar yet; it appears to be a bit hit and miss while using a fermenting crock makes it easy to keep the oxygen out. If you are going to try it in a jar then use a one way valve – this will allow any oxygen out but not let new oxygen back in.

How do fermenting crocks work?
It is just a container with a special top with a moat in it that you poor water in, and the lid sits in this moat, meaning that air cannot get in. Air from inside (the original air and the gasses produced by the bacteria) are allowed to escape via a couple of small nooks in the lid; they work to let air out but not in.

The other thing it comes with are some weights, usually ceramic which help to hold the cabbage under the salt water. This again helps to keep things anaerobic.

You don’t need a starter or anything like that, the bacteria naturally on the cabbage itself are what will multiply in the fermenting process. The only ingredients are cabbage (obviously), water and salt. Last time I used a standard cabbage, this time it is an organic one. I think either should work fine.

So, fermenting with a crock. They can be quite expensive. I bought mine, a second-hand 5 litre one made by Gairtpf for £20 on ebay. It was open but never actually used. They are heavy so you can get them for a bargain if you are local to the seller.

Things you’ll need
Cabbage (go figure)
Any other veg if you want, such as carrot or onion. I plan on trying this next time.
Water (I use natural mineral water but tap water would be okay)

First, before you begin, make sure everything is really clean, but also rinsed well to ensure there are no antibacterial agents left about, especially inside the container, as they may interfere with what we’re trying to do here.

My cabbage weighed 1.6lb. I used two cabbages last time, which turned into three or four large jars at the end of the process. But I didn’t eat it all (did I mention that I don’t like this stuff because it tastes like sour cabbage?….oh). Take two big outer leaves off the cabbage and set them aside. Shred the rest of the cabbage. It doesn’t matter how finely.

sauerkraut2Once you have shredded the cabbage, you add it to the crock in layers with the salt. Once it is all added you are supposed to pound the cabbage to get it to release its liquid from inside. You need approximately one tablespoon of salt per 1.5lb of cabbage. I did this but because I have ME/CFS I have little strength, so I just do a little and it seems to work fine even though it is not well pounded. The salt pulls water out of the cabbage, through osmosis. 24 hours later (or right away if you get knackered like I did and just want the ordeal to be over) you add the two leaves that you set aside, on top (this helps to keep the shredded cabbage from floating to the top) you place the weights on top of everything and then add enough water to just cover the cabbage and the weights.

Now you cover the Fermentation crock and fill the moat with water. Remember to check the moat daily as the water will evaporate and you will need to top it up. If you are making it in a jar then put the lid on it. Place it somewhere coolish (ideally, 18 degrees C, but room temperature is fine).

How do you know when it is done?
pH. It generally takes 2-4 weeks and as discussed above, the bacteria in the pot changes over time. So you will get different bacteria depending on when you decide to tuck in, and perhaps this will influence when you consider yours ready.

Last time I made sauerkraut it took 3 weeks. I tested the pH at two weeks and that told me it wasn’t ready (though it would have been safe to eat). After three weeks I was down around 3.6 which is where you want to be if you want completely cured sauerkraut. So get yourself some litmus paper.

Once it’s ready it keeps really well. You put it in a jar with a lid and cover it in the brine. It does not have to be refrigerated but it is a good idea and will extend its shelf life. You do, perhaps, start to get used to it once you eat it, and I suspect that if you grew up eating it, rather than say custard doughnuts, chocolate or pretzels, then you may even have convinced yourself that you like it. Personally, I think the bacteria ate the good bit and left me the pungent nastiness that is sauerkraut because they hate me. But I’m still gonna eat it, not for my sake, but for my gut’s.

If you want to help people like me who suffer from ME/CFS who have waited a long time for world class research into our gut microbiome, then please check out the Microbe Discovery Project and consider helping out.

1. Plengvidhya V et al. Appl Environ Microbiol. Dec 2007. DNA Fingerprinting of Lactic Acid Bacteria in Sauerkraut Fermentations
2. Zhou N et al. J Dairy Sci. Sep 2012. Antibiotic resistance of lactic acid bacteria isolated from Chinese yogurts
Image credit: sauerkraut in jar – wikipedia commons.


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