Back to Ask the Brewmaster.
Question: What is a protein rest and what does it do for my beer?
Answer: A protein rest is a portion of the mashing process. Typically, it is the first step in mashing. To conduct a protein rest, add 1 quart of water to each pound of grain. Hold at about 120 to 135°F for 20 to 30 minutes. Then, proceed on to the starch conversion rest by adding another half quart of boiling water.
Adding a protein rest will improve the clarity of your beer and especially helps in the prevention of chill haze. However, there is some disagreement in the literature as to just why this happens. The conventional wisdom is that proteolytic enzymes break down the long chain proteins in the malt into intermediate length fragments called albumens, short length fragments called peptides, and some free amino acids. Since the longer-chain proteins contribute to chill haze, shortening the chains improves clarity. The intermediate length chains contribute to head retention while the amino acids are necessary nutrients for the yeast. Higher protein rest temperatures favor the intermediate-length proteins which contribute to good head retention. An excessive protein rest at the lower end of the temperature range will degrade too many intermediate length chains and cause poor head retention.
The controversy comes from the fact that the kilning process during malting destroys most of the required enzymes. Only under-modified low-kilned pilsner malt contains any significant amount. With the fully modified malts available today, most of the enzymatic action has already taken place during the malting process, making the step unnecessary. Hence, as a matter of simplicity, many brewers skip right over the protein rest and go straight for starch conversion. I find that whenever I do this, I get chill haze. This happens even with Gambrinus pale ale malt, a well-modified variety. This leads me to believe that pale malt indeed does have a significant amount of enzyme. I've further noted that in extract batches with crystal malt, the chill haze is especially bad. This makes sense, since the caramelizing temperature during crystal malt production is considerably higher. I've found that adding a pound of pale malt in with the crystal seems to cure this problem.
Given that the protein rest improves clarity, you can evaluate its worth based on the type of beer you are brewing. If you're making a stout, who cares? Skip the rest. However, if you're making a pilsner, a protein rest is probably worthwhile. Protein rests are also important if you are using other high-protein malts such as six-row malt and malted wheat. Also note that clarity can be improved by use of Irish moss or isinglass.