Home brewing can be a tricky science. Of course, there are home brewers who just throw it together and look forward to whatever brews. But making changes along the way, documenting every possible contingency and then tweaking it when it doesnít come out just right is the art of the master brewer.
The one question most brewers ask will always be how potent is their beer going to get. Itís not really all that scientific. You need to know a little math and you need to be aware of a few measurements as you brew. Other than that, itís a piece of cake.
A simple tool you will need before you begin brewing is the hydrometer. Youíll need an original gravity reading and a final gravity reading. The hydrometer can get those readings for you. It actually measures the relative density in a liquid. For instance, milk is a rather dense liquid while water itself isnít. So, youíll need a very specific hydrometer for low-density liquids where the 1.000 for water is placed at the bottom of the hydrometer for a more exact reading.
Original gravity is the reading you get before fermentation starts. After brewing, before you pitch your yeast, take a sample of the wort and pour into your graduated cylinder. Get the reading of your gravity from the hydrometer. Just to give you an idea, your reading might be around 1.060.
The final gravity reading is taken just before bottling. Youíll probably take several gravity readings until fermentation has stopped. Thatís when you get the final gravity reading. To give you an idea, your reading might be around 1.015. Remember to get as exact as you can because thatís where the fun begins. The more exact, the more precise your calculations will be.
Subtract the final gravity from the original gravity. Multiply by the result by 131 and youíll end up with the ABV. Alcohol by Volume is in a percentage and normally around 4 to 6 percent. In the above example, we would subtract 1.015 from 1.06 to get .045. Then, multiply .045 by 131 to 5.91, which is a very good beer.
If youíre not happy with that number, Germans laugh at your brew and call it Bottled Water, then by all means learn how to increase your ABV. Itís simple logic. We just did the calculations. We calculated the original gravity, which is gravity before fermentation. Then we calculated the final gravity, which is gravity after fermentations. If fermentation makes the liquid less dense and the less dense the liquid the higher the ABV, then we have to add fermentation.
In all your tweaking for taste and color, make sure you tweak for maximum fermentation. Learn about top cropping, bottom cropping and everything else that you can about how yeast affects your beerís ABV. Each batch should get closer and closer to the beer youíre trying to chase. Chase your taste!