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Fermenting Day


So the wort is cooled to room temperature. Potentially you could store it like that for a long period, as long as there isn’t too much air floating round in there but you probably want to get on with turning the sweet wort into satisfying beer. The thing that will take longest is rehydrating the yeast, if, like me, you are using dried yeast. Ideally, look up the instructions from the yeast manufacturer online but here is my routine.

Boil a decent amount of water, pour it into a jug and swill it round to cover the whole internal surface. This sterilises it – you can then pour out most of the water, leaving about 50ml, cover with clingfilm and stick in the fridge. You are waiting for water to cool to about 25-30°C, so keep an eye on it. While this is going on, get the VWP out and do some more sanitising. You will want to take a gravity sample, so that’s a sample tube, hydrometer and something to draw out your sample of wort. I use a syringe but, at a push, a suitable glass or jug would work. Also make sure your stockpot is cleaned and sanitised.

The original gravity sample is important if you want to know how strong your beer turns out, so make a note of it. If you aren’t close to the temperature the hydrometer was calibrated for, find an online tool to calculate the actual gravity. If the gravity reading isn’t close to what the recipe expected you can either live with it or make adjustments – dried malt extract or brewing sugar to increase gravity or water to dilute it down. I normally stick to simply making a note of what the gravity is.

By now, the water in the fridge should be approaching temperature so you are almost ready to start on the yeast. Since I normally brew less than the standard 20-25l, I tend to use half of an 11g packet of yeast; this is slightly over-pitching, but is fairly easy to measure if your scales are accurate. Sprinkle over the top of the water but don’t stir. The jug, still covered with the cling film, will now sit outside the fridge. Now you are into a process of gradually getting the yeast used to swimming around in sugary liquid, creating alcohol.

After ten minutes, give it a gentle shake. Wait another ten minutes or so and add about 1/3 of the contents of your sample, with another gentle shake. Repeat after another ten minutes. Ten minutes on and… pour the yeasty liquid into the stockpot. Now pour on the rest of the wort. Don’t worry about most of the kettle trub getting in there – it doesn’t seem to hurt. You are looking for a generous pour which aerates the mixture well.

That’s it. The yeasty magic which turns wort to beer should now be underway (aside: in Medieval times, yeast was sometimes known as God-is-goode). Ideally, you’ll have something like a brew belt to apply some heat and an easy way to monitor the temperature (I use my Raspberry Pi, a temperature probe and a simple bit of software I wrote) but somewhere that keeps a reasonably constant temperature round about 17-20°C would suffice.

Fermenting is underway but, if you followed the instruction, you will still have about 1/3 of the sample left. What to do with that? Go on and sample it. It won’t give you an exact idea of the final taste but it’s a treat you can enjoy!