Beer School. Jonny Garrett

gravity is a tricky little game played by brewers once the mash is over. The malt has been steeped, stirred and broken down to release its sugar, so now the brewer needs to collect it. This is done by opening up the bottom of the mash tun and pouring hot water (around 168ºF) in from the top. This water filters through the grain, collecting all the sugar before making its way into the next vessel, the kettle. This process is known as “sparging” or, when using a second vessel called a lauter tun, “lautering.”

      As it goes through, the brewer takes a sample to measure. From that, he works out how much water he’ll need to get the right original gravity. This happens several times during the so-called “run off” because the first few litres of wort are usually more concentrated than the last few. Lovely as water is, the last thing he wants to do is add too much and end up diluting the beer.