The Mash Tun

We mix the crushed malt with hot water to make the mash — something that looks like warm oatmeal and smells like fresh bread. The single most important bit of chemistry in brewing happens right here.

The malt's enzymes wake up in the warm water and start cutting long starch chains into shorter sugars. Temperature is everything. Around 63 °C, beta-amylase produces lots of fermentable sugar that yeast will eat completely — giving a drier, stronger beer. Around 72 °C, alpha-amylase takes over and leaves more unfermentable sugar — giving a fuller, sweeter beer.

So a brewer doesn't choose sweetness by adding sugar; they choose it by setting a thermometer. A couple of degrees here is tasted in the glass.

After 60 to 90 minutes an iodine test confirms no starch remains. Conversion is done, and we move on.