Tuesday, July 26, 2011

Food Science: What happens when you rinse kefir grains?

So, ignore the name of my blog for this post.  That's right.  It's time for some food science.  But in my defense, it involves traditional food (kefir) and good ol' falsifiable science.  That's right.  I did a an experiment to determine whether or not one should rinse kefir grains before adding them to a fresh batch of milk.

Kefir is not a popular food, at least not compared to its yogurt-y cousin.  So when you decide to go out and make it on your own, you have to rely on what you can dig up on the internet.  And true to the internet's reputation, you can find any possible answer for whatever question you are asking.  One simple question that I had was whether or not I should be rinsing the grains between batches.  The information I received with my grains said I should not rinse them.  However, Nourishing Traditions seems to suggest that they should be rinsed.  There was only one way to find out.  I hypothesized that rinsing the grains would blunt their capacity for producing kefir, and therefore produce a milder kefir.

Fig 1.  Separated and weighed to 10 grams

The grains were rinsed and randomized.  Two groups, each weighing 10 grams (g) and containing 18 grains (Fig 1), were formed.  Most batches were made with 8 ounces of organic pasteurized whole milk; the last couple of batches were a bit over 8 ounces to accommodate the increased fermentation.  Fermentation was 12-14 hours per day. Clean jars were used each time.

Fig 2.  Kefir preparation.  Clean jars, 8 oz. milk, cover with paper towel. 

The time and temperature were not always consistent.  However, because the jars were adjacent to each other at all times, any day-to-day variation would affect each group equally, and would therefore not bias the results.  The only difference between the groups was that the experimental (washed) group was rinsed under cold tap water in a stainless steel strainer until curds were removed, roughly 10 seconds.  The control group was simply placed in a new batch of fresh milk.  The experiment ran for 11 days, and on the 7th and 11th days, both groups of grains were washed and weighed, and the two different batches were tasted by a blind taster a.k.a. the girlfriend.

Both groups increased in weight at the same rate.  However, the grains in the unwashed group were more dense than the washed group on day 7 (0.67 g/grain vs. 0.48 g/grain) and on day 11 (0.74 g/grain vs. 0.51 g/grain).  Thus, rinsing reduced the density of the grains by 30%, and produced many small grains (Figs. 3-5).

Fig 3. Unwashed (left) and washed (right) groups at the end of the study.

Fig. 4 Results of control (unwashed)
Fig 5.  Results of experimental (washed) group.

Tasting results were consistent between the 7th and 11th day.  Both batches of kefir reportedly tasted as kefir should, and both batches were similarly thick, both in the glass and in mouthfeel.  However, the unwashed kefir was "definitely more sour."  Furthermore, the washed kefir had a lighter effervescence with smaller bubbles and "a more full kefir taste."  The unwashed group appears to ferment faster, as there was usually more whey present (Fig 6).

Fig 6.  The unwashed (left) was usually more fermented.

This experiment demonstrates that rinsing kefir grains between batches produces more and smaller grains than when grains are left unwashed.  Furthermore, these rinsed grains tend to produce a milder kefir.  While I can surmize that this occurs because the unwashed grains produce kefir at a faster rate (and therefore make a more kefir, kefir), that will require another experiment.

I'm definitely confident in these results, but I would love to hear other peoples' experience with washing their grains.  The results might have been more dramatic had I not rinsed and weighed the grains mid-experiment, but then again, this added a bit of reproducibility within the study.  Unfortunately, I was not blinded to the treatment group.  And come to think of it, the kefir wasn't blinded with a placebo.  I already anthropomorphize my kefir grains enough as it is, but perhaps they knew what group they were in...

So, what can we take away from this bit of food science?  There are likely many recommendations for treating kefir grains because there is no obvious best way.  While I would argue that the density produced by leaving the grains unwashed is evidence of "healthier" grains, if you prefer the taste of a mild kefir, then you would be better off rinsing them, at least occasionally.  Or, as I've started doing, rinse the grains on warmer days or when you might make it home late and risk over fermenting the kefir.  Either way, it's between you and your kefir.

Now, it's time for a kefir smoothy.  Theory into practice, I suppose.  Cheers!

This post is shared on Real Food Whole Health's Traditional Tuesdays.


  1. Great research! Never tried kefir and kefir products though, but I think it is a good food to be part of.

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  2. Woops! Sorry, but I am not a woman/mom.

    Although I can understand the confusion, as the food blog community does seem to be saturated with moms :)

    1. Your experiment confirms what I noticed regarding size and density. I was told to rinse them when I got my first batch. Personal issues caused me a lapse for 2 or 3 months and they went slimy. I got another batch a couple of weeks ago from a guy who says not to wash them ever, because it removes the smallest micro-organisms and I haven't rinsed those. The grains are much larger and denser. HOWEVER, your experiment is only superficial. I'd like to see one that compares the good bacteria/organisms of the rinsed versus non-rinsed, from the same non-rinsed batch. I guess you would have to be a chemist to do that or at least, you would need a very fine microscope. I suppose identifying each micro-organism wouldn't be an easy job for a layman. Such an experiment would likely show whether or not there really is a loss in micro-organisms in the rinsed batch, what MO's were lost in weekly rinsing, if any, compared to a non-rinsed batch. Such experiments are usually not conducted unless there is some huge profit to be made - not the case here.

  3. Thanks for the informative and detailed experiment. I also wondered about the difference between washed/unwashed kefir and had read conflicting answers. This was very helpful!

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  5. Wouldn't rinsing remove Kefiran, a slimy substance said to be very healthy? http://users.chariot.net.au/~dna/kefiran.htm

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  10. What about the chemicals in your tap water? maybe next one you can use spring water or filtered.

  11. Thanks for looking into this as I had the same question. Wouldn't the increased weight be attributed to the excess liquid that was not washed away? Since that liquid is sticky wouldn't that also account for the washed group having a larger amount of smaller grains? (since they are not held together) It would be interesting to compare the microbial content between the two.

  12. Thanks for looking into this as I had the same question. Wouldn't the increased weight be attributed to the excess liquid that was not washed away? Since that liquid is sticky wouldn't that also account for the washed group having a larger amount of smaller grains? (since they are not held together) It would be interesting to compare the microbial content between the two.

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  15. I appreciate anyone whom goes to the trouble of answering questions and sifting through the mire of the Internet, where the most paid for answer wins. A fundamental flaw here however, is that you have used tap water. You never, ever use tap water. I ferment quite a few things, chlorinated water is an antibacterial and fermenters are bacteria Farmer's. For what it's worth, I never rinse but if I was to it would be with milk.

  16. I come from Chile and I grew up eating what we called yogurt from small grains which now I believe is kefir. The grains there, however, are fat and the final product is a rather sour liquid. Now I got my own grains here in the US and they are considerably smaller. I did started the process like we do in Chile, placing them in milk and then rinsing them with a bit of tap water the next day after taking the yogurt out. However, as the grains here seemed to multiply but now grow, I was wondering if the water rinsing had anything to do with it. I am glad I found this research. My grains are multiplying, as the chart above shows, but not necessarily growing. The kefir I get is very nice, not so sour.
    My only puzzle now is why the Chilean kefir grows so much bigger even though the are water rinsed?

  17. After a while did the washed kefir begin to ferment as fast as the unwashed kefir did?

  18. possible confounding variable: stainless steel container?