Tuesday 14 April 2020

Operation Infinite Yeast - Growing Your Own Yeast

There are lots of ways to make bread, and to be honest none of them are hard. But they all come down to one thing - making a dough that when cooked doesn't become so heavy and stodgy you don't want to eat it. The way we're most used to is to use yeast, and of course thats the bread you're most used to buying. 

In normal times I would suggest buying dried yeast to keep in the cupboard in an airtight container for whenever you want to make bread. Its what I've done for years, but apparently now that everyone has been panic buying you just can't buy yeast. So, you're looking at your last little bit of dry yeast and you're wondering what you're going to do to make bread going forward? Well, you've got lots of options, but if you want something most like a loaf of bread that comes down to four techniques. Soda bread, where you use baking soda to raise the bread, saved dough (as covered excellently by Kate here) so you cultivate yeast in the dough and save some over for the next loaf each time, sourdough which is the use of wild yeast and bacteria cultivated from the flour itself, and lastly you can maintain your own yeast culture. 

Basically yeast is a microorganism, its a fungus but a single celled fungus, unlike the molds and mushrooms you're familiar with. And if you give it the right conditions it will grow, and you'll get more of it. But you need to make sure that its got enough of a run up what you're going to grow it in to make sure that what you get is actually your yeast, and not something else.

So, in a few steps, here's how to make your own yeast culture.

1. Seed Culture


This is a bit of a technical term, sorry for that. But in most practical applications of microbiology one of the most important things to do when trying to use microbes to convert any one natural material in to anything else (here its 'flour' into 'more yeast and bread') is to make sure you've got the right microbe growing very, very fast to ensure it outcompetes everything else. If you don't do that here you'll end up with a sourdough rather than a yeast culture, which is delicious but slower to bake with.


So here I recommend making up a seed culture. Get a clean jar and pour in about 100-150ml of water, and stir in a teaspoon of malt extract, half a teaspoon of yeast extract (marmite) and about a dessertspoon of sugar. Cover it, and let it cool to blood temperature. When its cooled, add in some of your dried yeast, a little will do, and stir it again. Again leave it loosely covered and leave it somewhere warm. 

By morning, it will be cloudy, and probably very, very fizzy. Don't shake it, but stir it very gently or there is a very good chance it'll end up all over your kitchen counter top. And this is your 'seed' or 'starter' culture. Its a big, liquid mass of very fast growing yeast cells, and they're ready to out-compete everything in your flour.

2. First Flour Ferment

To 3 dessertspoons of bread flour, add 2 dessertspoons of your starter culture, in another clean jar. Stir it, cover lightly. Later in the day, when its good and fizzy again and you can see air bubbles appearing, add another 2 dessertspoons of water, and 3 more dessertspoons of flour. And by bed time it will be like the jar of fast growing yeast to the right.

So the fast growing yeast you put in this morning has been making enzymes like something called amylase all day. The job of that enzyme is to turn the starch in your flour into smaller carbohydrates (sugars) that it can eat. Bread flour also contains a lot of gluten, which is a protein, and the yeast uses both of these and all of the trace nutrients in the flour to grow and make more yeast. Actively growing yeast generates gas, which you can see as bubbles, and bubbles make noise which you'll hear if you click on the video on the right.

And this is almost ready to use, but probably not yet, because its almost certainly nearly bed time. You can bake your first loaf with this tomorrow afternoon. Put your jar of yeast culture in the fridge overnight.

3. Wake Your Yeast Up

Its not literally asleep, but it has slowed down over night. If you take this and mix it in to your bread dough its just going to sit there and sulk. To make this work you really want your yeast to be growing very fast, and very actively. At this point I add in half a teaspoon of sugar, 3 dessertspoons of flour, 2 of water, mix it in and cover it loosely and, crucially, leave it somewhere warm. Behind the telly, on a warm window ledge, wherever you have. In a few hours you'll be ready to make bread.

4. Make Bread, and Save Your Yeast!

I use most of my yeast culture up on a loaf, saving about a dessertspoon full, and to that I add another dessertspoon of flour, a little less of water, and I let it grow. When it fizzing again and forming air bubbles it goes back into the fridge until I need it again.

As long as you don't kill it, you've got yeast forever. Feed it up to the same volume you started with before putting it in the fridge, and be sure to wake it up in the morning with a fresh feed before using it, and it'll just work.

As for the bread, well, the worlds your oyster. Its basically a live yeast so you make the dough up any way you like - this was one of my standard malted wholegrains, but it'll work for anything you'd use a bread yeast for. 


And thats it - if you can master this then congratulations, you're a yeast farmer. Good luck, and happy baking.

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