Milk Kefir Sourdough Starter

In my Universal Pancake Recipe, I mentioned that a little milk kefir mixed with flour makes a good, low-commitment sourdough starter. Today, I'm going to go into a little bit more detail about how that works, and how to make and maintain your starter.

Let's start with the basics: What is sourdough?

For the purposes of this blog, sourdough is any dough which uses a starter culture containing a diverse mixture of wild yeasts and bacteria. Store-bought yeasts consist of a near-monoculture of the yeast species Saccharomyces cerevisiae (the same species as the yeast used for brewing beer, but a different strain). A sourdough starter contains both Saccharomyces cerevisiae and lactobacillus bacteria (the same stuff that makes lacto-fermented pickles and turns milk into yogurt). Unless you are growing your culture in a tightly controlled laboratory environment, it will also become home to lots of other types of wild yeast and bacteria, creating its own little ecosystem.

When flour is mixed with water, the enzyme amylase starts to break down starches into sugars, which are then consumed by the bacteria and yeast. The yeast convert sugars into alcohol and carbon dioxide. In brewing, the carbon dioxide escapes through the airlock and the alcohol is retained. In baking, the alcohol gets cooked off and the bubbles of carbon dioxide are trapped in the dough.

The lactobacillus bacteria convert sugars to lactic and acetic acids, lowering the pH of the dough to around 3.8. This is what gives sourdough its sour flavor, and adds complexity to the taste and aroma of bread.

If you don't have a friend who can give you a starter, you can buy one from any number of companies, but the traditional way of starting a sourdough is simply to mix flour and water and wait for it to start bubbling. Flour naturally contains a wide variety of bacteria and yeasts, as does the air in your kitchen. As long as you continue to feed your culture fresh flour and water every day, it's only a matter of time before you will develop your own, 100% local sourdough starter.

I've done this before and it's very satisfying, if a bit unpredictable. (In our kitchen in Scotland, our native sourdough was only so-so for baking, but it made incredible booze.) The trouble is, cultivating a sourdough starter from scratch takes several days, and then requires that you use or discard some and feed it fresh flour and water every single day.  It is possible to send your starter into hibernation by putting it in the fridge, but then it takes a few days to revive it enough to start baking with it again. If you're like me and your energy levels and areas of interest fluctuate wildly from one week to the next (or one day to the next), that can be a bit discouraging.

That's where milk kefir comes in.

Kefir is a cultured milk drink inoculated with yeast and bacteria. The result is similar to yogurt, but thinner (similar to cultured buttermilk in consistency) and very slightly carbonated due to the yeast. Unlike yogurt, which is made with thermophilic (heat-loving) bacteria, kefir contains mesophilic (middle-loving) bacteria, meaning that it will culture just fine at room temperature. There's no need to pre-heat the milk or keep it warm overnight. Because it's so easy to make and useful for so many different things, we pretty much always have a little jar of milk kefir culturing on the counter.

Rather conveniently, kefir contains many of the same types of yeast and bacteria that are found in sourdough. This means that when the urge to bake suddenly comes upon you, all you need to do is mix a little bit of kefir with flour, and voila! You have a sourdough starter. When you get tired of baking, just use up the last of your starter, secure in the knowledge that you can whip up another batch at the drop of a hat!

By using kefir, you're skipping the process of trying to attract wild bacteria and yeast, almost as if you got a dollop of established sourdough starter from a friend. It's had a change of environment and might take a day or two to reach peak performance, but all of the beneficial microorganisms are already present in large numbers.

It is possible to mix a starter and bake with it the same day, but your colony of bacteria and yeast will be much more vigorous if you let it get used to its new flour substrate by letting it acclimate at least overnight and feeding it with flour and water at least once before baking. If you're in a hurry and absolutely must bake with it the same day, it really is essential to keep your dough/batter warmer than room temperature while it rises.

It shouldn't surprise you to learn that I don't measure the amounts of flour or liquid when making my starter; I pour a little heap of flour into a jar and stir in milk kefir a little at a time until it has the consistency of a thick batter. I tend to use brown rice, sorghum, cassava, or an all-purpose blend in order to keep the flavor fairly neutral, but any kind of flour will work.


If you've used sourdough before, you can skip the rest of this post. After the initial mixing of kefir and flour, treat your starter exactly as you would an ordinary sourdough. For those of you who might be new to sourdough baking, however, here are a few basic instructions:

You need to feed your starter every day. The accepted wisdom is to use or discard half of your starter each day, and then add more flour and water until it's back to its original volume. You're supposed to measure equal quantities of flour and water by weight (not volume!), but I generally just go by consistency, aiming for something like a thick cake batter.

When working with sourdough, hydration levels can affect the population of your starter culture. A wetter starter tends to favor bacteria, and a drier starter tends to favor yeast. If you notice your starter becoming sour and slow to rise, try feeding it more flour or less water. The yeast seem to need warmer temperatures than bacteria to thrive, so you might also try leaving your starter in a warmer place.

If you're baking like a mad thing, you can of course feed your starter more than once a day, or in larger quantities. Whenever your starter has bubbles all through it, it can handle another feeding. If it isn't bubbling fast enough, try keeping it in a warmer place. (I'll sometimes set the jar on top of my mug of tea while it's brewing to speed up the process.)

I also tend to cheat on discarding half of the starter each day. I hate throwing out perfectly good food, but rarely have the energy to make bread on a weeknight, so here's what I do if I want to keep a starter going from one week to the next: once I've finished my baking for the weekend, I'll leave just a spoonful of starter at the bottom of the jar. Each day, I'll feed it enough to double its volume, but because I've started with such a small amount, by the time Friday rolls around there's just enough to make a batch of bread dough. I'll use and feed it generously during the weekend, and then use up all but a Tablespoon or two on Sunday.

If you're interested in learning more about milk kefir, sourdough, or gluten-free sourdough, there's loads of good information over at Cultures for Health. (Pro tip: their free ebooks are a compilation of all of the relevant articles on their website, and are actually quite good. EVERY TIME you load a page or mouse over the menu of your browser window, you will be confronted with an annoying pop-up ad inviting you to download the aforementioned ebooks. Just get the ebooks and you will never need to visit their site again.)

I hope you've found this little introduction to milk kefir sourdough useful. If you try it, let me know how it goes and what you've made!