Mashing With a Protein Rest


Question: I have two questions for which I can’t get good answers from local homebrew supply stores.

I am a new full-mash brewer. I have been using highly modified two-row pale malt with 10% adjuncts. When mashing on cooler days, I find it hard to keep a steady mash temperature in my plastic mash tun. Typically it drops to about 135 °F (57 °C) after 30 min. I wonder if I am performing a protein rest by accident? Is a protein rest for highly modified two-row malt beneficial, even though it is technically not required? Will I help the mash if I add a higher percentage of adjuncts such as Carapils or crystal?

Dave Miller: I doubt that you are getting much of a protein rest with your mash procedure. Most of the protein-converting enzymes in malt are active between 113 °F and 140 °F (45 °C and 60 °C). At higher temperatures, they are deactivated (a fancy chemical term for cooked). I assume you are starting your mash at around 150 °F (66 °C) — it sounds like you are trying to do a single-temperature infusion mash — so most of the protein-converting enzymes will be out of commission before the temperature drops back to protein rest range.

If you get any protein conversion, it certainly won’t hurt anything. The only problem you can have from a protein rest is that, if you let it go on too long, you may get so much protein breakdown that you don’t have enough large and medium-sized protein molecules in your wort, to the detriment of body and foam retention. For the reasons I mentioned in the previous paragraph, though, I doubt this could happen to you.

If I were you, I would be more concerned about the starch conversion. The speed and efficiency of the starch-to-sugar breakdown depends very much on temperature, and I would be leery of any process that did not give the mash at least 0.5 h at 150 °F (66 °C) or higher. I know that the big commercial breweries often show conversion in 10 min, but their malt is crushed a lot better than ours. They use multistep mashes that allow the grain interiors to absorb water and soften before they hit the critical temperature.

One indicator of whether you are getting full conversion is the extract yield of your grain; however, problems in other areas, including sparging, can also produce low yields. Another possible indicator is starch haze and a starchy taste in the finished beers.

You would almost certainly get better results if you did your mashes in a kettle that can be heated on the stove, which would allow you to maintain starch conversion temperature for 1 h. If you can’t use a kettle, at least wrap some insulation around your plastic bucket mash tun. I bet if you think about it you can find a way to redeploy your brewing vessels so you can heat the mash. Such an arrangement would even enable you to run a step mash deliberately, if you want.

A quibble: products like Carapils (dextrin malt) and crystal malt are not really adjuncts. Adjunct is a specific technical term in brewing and refers to unmalted cereals, such as corn, which are used to augment the starches contained in barley malt. Adjuncts must be cooked before being added to the mash tun. The best form of adjuncts for home brewers is flakes, which have been precooked during the manufacturing process.

The grains you refer to are called specialty malts, which are made by modifying the malting process in various ways. They require no cooking. The specialty malts you mention are little affected by protein-degrading enzymes, though some others, such as rye malt or wheat malt, do contain considerable protein and would be affected. When using such high-protein specialty malts, or high-protein adjuncts like oat or barley flakes, a protein rest is a good idea. In such cases, the protein rest must precede the starch conversion rest. For more discussion of this issue, see the last question in this article.

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