Process: Milling, Mashing, Lautering

The first phase of brewing beer is the extraction of sugar from malted barley. This sugar is what yeast will consume to produce alcohol. 

Malted barley contains both starches and the enzymes that will break those starches into sugars. The starches are extracted with hot water, and the temperature of that water effects the properties of the wort, the sugary liquid that will be fermented into beer.

Milling

The beer brewing process begins with the milling of the grain. The idea here is to increase the exposed surface area of the barley malt - similar to the process of grinding coffee beans before making coffee. The starches are then extracted by soaking the milled grain, or grist, in hot water.

Too course a grind will result in an incomplete extraction of the starches.

Too find a grind may result in the grain forming a thick cake that does not allow the liquid to drain easily. This lack of drainage is called a stuck mash. Sometimes additional husks (also called hulls) are added to the grain to promote proper drainage.

Milling the barley too finely also damages the husks, which act as a filter bed when draining liquid from the crushed grains. These damaged husks will release tannins, which will give an undesireable astringency to the finished beer.

Mashing

The next step is to soak the milled grain in hot water in a process called mashing.

Brewers call water liquor, but for clarity of explanation, I'm going to call it water, but you should know that the proper brewing term for water is liquor. 

(I used to work in a distillery. Visitors often asked why we used liquor to make liquor. Explaining this often caused even more confusion, so now I tend to avoid technical jargon.)

Soaking the milled barley malt in hot water accomplishes two things:

First, it liberates the starches from the grain and puts them into solution. Think of steeping a tea bag to make tea. Brewers call this barley tea "wort" (say it "wert").
   
Starches are large molecules composed of many sugar molecules linked together. Yeast can't consume starch, but they can consume sugars.

Malted barley is used for brewing because it contains the enzymes necessary to convert starches to sugars.
  
Soaking the barley in water activates these enzymes.

The temperature of the mash water alters the effectiveness of those enzymes, so the temperature of the water effects the sugars made available to the yeast for fermentation.

An illustrated guide to mash temperatures 

There are several types of sugars released during mashing, and the most abundant of these sugars is called maltose.

The main enzyme in this process is amylase. This enzyme exists in two forms, labeled alpha and beta. 

(Side note: amylase is also present in human saliva and sweet potatoes, both of which can be used to brew beer).

The temperature of the mash is about 140 - 160 degrees F.
 
Higher mash temperatures favor Alpha-amylase, which does not do as thorough a job as Beta-amylase does at converting starch to sugar.  

Alpha-amylase leaves behind lots of unfermentable sugars. Since these sugars don't ferment, this wort will produce less alcohol. The sugars that remain in the wort aren't necessarily sweet, but they contribute to a fuller body in the finished beer. 

A lower steeping temperature will favor Beta-amylase, which will result in a more complete conversion of starch to sugar. This wort will ferment to a beer with lighter body and higher alcohol than if the mash was done at a higher temperature.

Variations on the Mash

Adjunct grains usually require higher mash temperatures than barley, so these grains are mashed first. The mash then cools before the barley is added.

Decoction mashing is a traditional German technique. Pilsner Urquel is an easy to find Bohemian pilsner made with a decoction mash. In decoction mashing, a portion of the mash, grain and all, is removed and boiled. The boiling results in increased flavor extraction and some caramelization of the sugars. The boiled portion is then returned to the mash vessel, called a mash tun, raising the temperature of the mash water.


Lautering

Once starches have been extracted and converted to sugars, the wort must be separated from the milled grain in a process called lautering. The mash tun has a perforated false bottom used to retain the spent grain while the wort is drained off.

Sometimes additional heat is applied to stop the enzyme activity and to make the wort flow more freely. This step is called the mash out.

The first bit of runoff drained from the mash tun often contains debris and proteins. This initial runoff is recirculated into the top of the mash tun so that the grain bed can act as a filter. This is step is called vorlauf.
 

After the wort has been drained, the grains are then rinsed with additional hot water in a process called sparging. This rinsing is done to extract as much sugar as possible from the grains. Excessive sparging, or sparging with excessively hot water, can leach tannins out of the barley husks. This can make the beer astringent.

The resulting clear wort is now ready for boiling, which I'll cover in the next post.

For additional research:

How to Brew 
by John Palmer
Ch. 14 - 18

Mastering Homebrew 
by Randy Mosher
p. 121 - 145