What is SRM? According to the American Homebrewers Association, SRM stands for Standard Reference Method. SRM is the unit of measurement for...the colour of beer! But first, to understand SRM we'll have to know what causes colour formation in beer.
Why does beer change colour?
The two main reactions that cause a colour change in beer is the Maillard reaction and caramelization.
The Maillard reaction is the reaction that occurs when we toast bread. It is the reaction of amino acid with a sugar molecule in the presence of heat and causes a brown colour in beer.
Caramelization, on the other hand, is the reaction of sugar molecules with high heat! Also creating a browning colour in beer.
Playing with colour...and flavours!
Playing with these two reactions gives the brewer more control to achieve certain colours and even flavours!
For example, someone looking to make a bready tasting beer may want to encourage the Maillard reaction in their beer! On the other hand, a brewer looking to have a nutty or caramel flavour may want to encourage a caramelization reaction to achieve this!
Let's get down to it; What is SRM?
Now that we know what reactions take place in the colour formation of beer, let's talk about SRM.
To measure SRM, a brewery need a spectrometer, which essentially uses light waves to measure the SRM. (It's a bit more complicated than that. Read more on the BeerSmith Home Brewing Blog)
This in turn tells the brewery what degree of colour the beer is. The higher the number, the darker the beer. This seems complicated for just measuring colour, so why would a brewery decide to do this? By measuring SRM, a brewery can keep its product more consistent in colour. Ensuring the consumers get the same product every time they buy it!
A cool way to help understand SRM and colour in beer is to get a tasting flight at the Trois-Lacs Microbrewery and see what SRM each beer is and compare it with the colour of the others. This will help get a better grasp on what SRM is and how it relates to beer colour!
Remember; Beer is as much art as it is science.