Beer Fact Friday: Milling
For the next several weeks, we’re going to go in-depth into every stage of the brewing process, from start to finish. Today we touch on the first step that occurs at the brewery: milling.
Most of a beer’s color, sweetness, and alcohol content is imparted by malt: grains (barley, wheat, rye, or oats) that have undergone special processing prior to their arrival at the brewery. In the case of barley malt—the malt most commonly used by brewers—the grain arrives at the brewery in the form of whole kernels, with an outer husk protecting a seedling known as the “starchy endosperm.” It’s this core that the brewer needs to access, because it contains flavorful starches and sugars as well as the enzymes that will assist in breaking them down into fermentable components.
So how does a brewer gain access to the endosperm? Milling. Milling is the physical act of crushing malt kernels into smaller particles in preparation for the next stages of the brewing process: mashing and lautering.
The most common type of mill found at breweries is a roller mill—essentially a pair of cylinders that spin downward in opposite directions and at different speeds. As the grain passes through, the rollers press and shear each kernel, allowing access to the endosperm while leaving the husk mostly intact. (At least, that’s the goal.) When carried out with dry grain, the milling process can create a large amount of malt dust, which is highly flammable and can be ignited by, for instance, sparks created when metal objects inadvertently scrape the rollers. Due to the danger of explosion, many brewers set up their mills in special blast-proof rooms separate from the rest of the brewing equipment.
The process of milling malt is a delicate balancing act. Crush the grain too finely and you end up with something resembling flour: You’ll be able to extract every bit of the grain’s sugars and flavor when you combine the grain with hot water during the mashing stage, but you’ll also end up with a clumpy, sticky goop that’s nearly impossible to work with. Conversely, a coarse grind will make mashing and lautering easy-peasy, but you’ll likely end up with a weak, watery wort lacking in flavor. Because the size of grain kernels can vary year over year or between different malt providers, brewers must constantly tweak the settings on their mills to achieve the perfect grind.
Once the grain is milled, it’s moved inside a brewhouse vessel called a “mash tun” in preparation for the next stage of the process: mashing. We’ll cover that one next week.
Beer Fact Friday is our weekly exploration of the topics that make beer the world’s most interesting beverage. Check back here next week—or follow us on Facebook, Instagram, or Twitter—for more fascinating beer trivia.