Some of us may remember Griff Rhys Jones telling the nation this back in the 70s, and basically he hit the nail on the head: yeast turns sugar to alcohol, and the more of the sugar it turns to alcohol, the drier (sorry, Griff, cleaner) it gets. [End of obscure TV advertising references.]
Now, if you start with fruit juice (wine, cider) you are starting with a mixture of water, sugar, fruit acids, and other flavoursome things all provided ready-made in a handy container (grape, apple) by Mother Nature. And in fact, the good lady can even provide the yeast, too, as what happens in the apparently true stories of pigs getting drunk on windfall apples.
But what about cereals? I mean, you can make bread, and cakes, and muesli and porridge, but a drink?
Well, they are all full of starch, which at a molecular level, is lots of sugar molecules joined together in a long string. The trick here is two-fold: get the starch to turn to sugar (’cause the yeast can’t do that), and get it out of the grain, and into the water where the yeast is waiting hungrily.
Barley is the king of cereals when it comes to brewing, because of what happens when you let it germinate: it produces lots of enzymes that start turning the starch into tasty sugars. Tasty for the yeast for the most part, but there are some that the yeast rejects, and which we humans rather like because it makes the beer taste, well, malty. So what the maltster does is wet the barley, rather like a loving gardening watering the new seeds, waits till the little sprouts start to appear, and then not like a loving gardener, toasts it! The toasting stops the germination (you want enzymes, not plants), and depending on how you toast it, gives you all sorts of interesting flavours and colours.
So, back to the malt. Each grain is like a pot noodle: it has starch and enzymes, and it just needs hot water. Just like a pot noodle, you need to open it (crush the grain) and add hot water (mashing, in the jargon). So you crush it, mix it with hot water, and wait.
After an hour or so, you have turned all the starch to sugar. See where we’re going with this? Good. Now we have to get the sugar out. You wash it. Simple. Rinse it out with lots of hot water (sparging or lautering in the jargon). Now you have a lot of brown, sticky, sweet, malty water (sweet wort to a brewer). It is surprisingly sweet. This really is one of the wonders of the process: start with horse-food, and end up with syrup!
Good to go then? Not quite. We like sugary goo, yeast likes sugar goo, but so do lots of nasty bacteria. Also, beer made like this is a bit dull to taste, so we add flavourings. Apparently, before about the 8th or 9th century, people used to use various herbs, but then the Church taxed them, so they started using a hedge-weed known as hops. So that was taxed, so they went back to the herbs, and so it went for a while, ’till people realised that the hops were too good to miss out on.
So: add the hops, and boil. This sterilises the wort, extracts bitterness and other flavours from the hops, and helps sort out some of the non-sugary stuff from the barley (proteins, for example).
Good to go now? Not quite. Yeast doesn’t like things that hot, so you have to cool it to room temperature, and put it in a nice sterile vessel. Now? Yes! Yes! Add the yeast, and watch it froth and bubble in its yeasty excitement. This, incidentally, is one of my little joys: the gurgling, happy bubbliness of fermenting beer!