Beer, kombucha, wine, hard liquors, water kefir, cider, wild sodas – they all have one thing in common – yeast!
The key for making fermented beverages is the use of healthy microbes. There are different ways of approaching the process. I will try to explain in simple words what happens when juice meets yeast
First of all - what is yeast?
Yeast is a single-celled microorganism, that multiplies when provided with enough nutrients (sugars and minerals). Yeast cannot be seen by human eye (unless it grows into a big colony) and appears all around us (even in air!) There are at least 1500 species, some of which have been domesticated by human and used for making delicious foods and drinks.
Now - how is yeast useful?
Yeast is a catabolic microbe that (with the consumption of sugars) creates alcohol compounds and carbon dioxide (CO2). And this is why to make beer or wine we need to pitch in an isolated strain of preferred yeast culture! This often comes in a form of dry granules. It’s the same with baking bread or making pizza dough! Whenever you need to make a fluffy loaf you can get a small sachet from a supermarket, dissolve it (activate) in lukewarm water and add to your flour mixture. For other applications liquid form of yeast is used. The process is called backslopping.
Backslopping? What does this vicious word mean?
Let’s take kombucha as an example.Backslopping is a term coined to a method of pitching yeast from a previous batch of a beverage, accelerating a new one. This liquid (old unpasteurized kombucha) is full of active yeast cells that jump straight to action in a fresh sweetened substrate. Backslopping is used in continous brewing of beer and can also be coined to making miso (seed miso) or lactoferments (such as kimchi).
Does yeast always create alcohol?
The answer is yes. Different strains of yeast have specific capability when it comes to handling certain concentrations of alcohol. This is why wine yeast and beer yeast are different. Even within the world of beer there are various strain that can build up more or less alcohol in the final product. When it comes to kombucha and water kefir – the alcohol by volume is very low (<1.2%). It’s because dominating strains of yeast in these types of beverages (called no-lo from “no or low alcohol”) cannot handle more than that. It will continue to multiply, but after reaching it’s limit – it will die and fall to the bottom of your fermentation vessel.
And what about CO2?
Carbon dioxide is the second byproduct of yeast activity. It also derives from a natural process. If the fermentation happens in an open vessel, then it will be pushed to the top of the liquid and simply disperse in the air. When the goal is to make a fizzy drink – the liquid has to be closed in a bottle or a container with a tight lid in the last stage of fermentation. Yeast continues to digest remaining sugars, but since CO2 has nowhere to go – it gets incorporated into the liquid.
Pretty much yes! But be careful! Bare in mind that CO2 closed in the bottles creates pressure. To much of it can lead an explosion and make a mess in the kitchen (not to mention that flying class can hurt you or people around you!). So be cautious and if you have little experience – I suggest to bottle your no-lo’s in plastic bottles. It is easier to verify if the pressure builds up and learn when your kombucha is refreshingly fizzy and ready to be served on ice.
You should also know, that yeast is active in specific temperature. And again – different strains prefer different temperature. In general a range between 15-25C is ideal for healthy growth of our helpful friends.
World of fermented beverages is vast and there is a lot of science behind it. On this portal you will find applications and theory explained in simple words. Brewing and high-proof alcohol making is not something I do often. But surely you should go to the blog section and explore more about other delicious non-alcoholic beverages!