Friday, September 5, 2008

Fermenting juice with milk kefir (Cheat's Apple Cider)

Hooray! I've just heard that Rebecca has some water kefir ready to send us - so soon I'll be able to ferment all sorts of different sweet drinks (assuming I can keep the kefir grains alive this time.)

In the mean time, my son and I have been fermenting apple juice using milk kefir. The apple juice is from our CSA and is very sweet and concentrated so it lends itself well to fermenting with kefir I think.

Opinion's divided over whether milk kefir grains can or should be used to ferment anything except dairy products. In Wild Fermentation, Sandor Katz writes that you can use them to ferment almost anything you like, as long as you give them some time to recuperate in dairy straight afterwards - so we thought we'd give that a go.

We've developed a system where we use half our grains to ferment apple juice, while the other half ferment milk or cream. Then we do another dairy ferment with all of the grains in together, then divide them in half again and go back to the beginning of the cycle.

I think that means that, taken over time, each milk kefir grain is spending roughly a third of its time in apple juice and the rest in dairy. (Any mathematically minded person able to confirm that?)

Here's some apple juice we fermented - with the grains still floating in it.

We call it our Cheat's Apple Cider. Apparently milk kefir can be very slightly alcoholic, so I suspect this apple juice is too, but only a little. When you take the first gulp, you get that warm feeling flowing through your veins ... but none of us have ever managed to get tipsy from it!


Anonymous said...

I have been fermenting apple cider with milk kefir grains for a few months now. I let it ferment so almost all the sweetness is gone and it has a nice head of foam when you pour it. If I drink a large glass of it, I do feel it. If I drink three, I'm very tipsy. However, it is a different sensation than I get if I were to drink beer or wine. I wonder if the alcohol created is the same, or if it has a slightly different chemical structure. BTW, I've also done grape, orange, and cranberry. They all work well, but my kefir grains are all purple now.

Anonymous said...

Hi, to clear this up, most kinds of yeast will consume sugars and turn them into alcohol. Different yeast strains will have different thresholds to which they'll tolerate the alcohol they produce without dying - this is their toxicity level. Yeasts will also eventually die if there's no more sugar for them to metabolize. The conversion of sugar to alcohol takes time, so the longer you let a yest 'do its thing' and the more sugar the yeast has been given to eat, the more alcohol you'll get (until the yeast dies and fermentation ends). Specialized wine yeasts strains (champagne, montpellier etc.) can handle ABV of up to 18-20% given the proper environment, but most yeasts will reach toxicity much earlier than that. Dairy Kefir is known to reach ABV of about 2%, but as far as I know that's largely due to the sugar (lactose) levels of milk. Kefir grains most probably also include yeast strains that are able to metabolize regular sugar (fructose / sucrose) that's in apple cider and since the sugar levels there are much higher, given long enough, they'll probably go much higher than the 2% they'd live otherwise. I've never seen any definitive research on how far kefir grains will go, but if you culture them to cider and they survive, you could probably manage to ferment most if not all sugar in the juice. Most natural juice / cider blends contain enough sugar to go up to about 5.5-6% abv without modification. If you let your kefir grains sit in your juice long enough, and fermentation persists until all the perceivable sweetness is gone, you've probably gone to 4-6%(you can easily test this with a hydrometer purchased at any home brew shop by taking a reading before and after fermentation). There's more science to it then that, but the basics are the same whether it's kefir grain or brewing yeast. Hope that helps! :)