Dear Mr. Wizard:
I like to do things the hard way. I usually start my mashes at room temperature and I use a good quantity of medium-modified grains. I'm still looking for the best protein rest time and temperature. My boosts are on the stove, so a 30-minute protein rest might be really 22 minutes, including the boost. What is your favorite time and temperature profile for good head retention? Is more than 30 or 40 minutes really bad? I rested my last batch for 13 minutes total.
Mr. Wizard replies:
Mash profiles mean different things to different brewers. There are many brewers who employ low temperature mash rests and their reasons differ.
If you have read any brewing literature over the last century, you will find references to the "protein rest." Historically, European malts were under-modified and required an extensive mash profile to yield the extract from these malts as well as separating the wort from the mash solids. The low-temperature rest, around 122° F, used in these long mash profiles was given the name protein rest because the bi-products of proteolytic activity were observed during this time. Indeed, the protein rest does increase the concentration of "free-amino nitrogen" or the amino acid ends of proteins, polypeptides and amino acids.
Recent literature indicates that most of the proteolytic activity in the mash increases the concentration of amino acids but does not significantly alter the molecular weight spectrum of proteins and polypeptides found in wort. The molecular- weight spectrum would change significantly if high molecular proteins were broken up in size.
Some believe that the products of protein degradation are "foam positive" and increase foam stability in the finished beer. I don't believe that significant changes in the molecular weight distribution of proteins and polypeptides occur during mashing at any temperature. Most of the demonstrable changes in protein size and solubility are seen in malting where proteases are active. Protease activity dramatically declines during kilning because proteases in malt are rendered unstable by heat and proteolytic activity in finished malt is very low.
However, there are enzymes that degrade beta-glucans (beta-glucanase enzymes), that do survive malt kilning and are active in the mash. Beta-glucanase activity is at its peak around 118° F, about the same temperature as the protein rest. Beta-glucanase activity can be very beneficial, especially when using under-and lightly-modified malts, which still have enough viscous, beta-glucan gums to cause wort separation problems during the lauter process.
This beta-glucanase activity is a more compelling reason for low-temperature mash rests than protease activity. I use a low-temperature rest for beers that contain under-modified or unmalted grains. For example, I use unmalted wheat for my unfiltered, American-style wheat and mash in at 120° F to cope with the unmalted wheat. I'm sure some will disagree, but those are my beliefs.
You have raised some good points about mash temperature and time. There are no hard and fast rules because enzyme activity is governed by both enzyme and substrate (what the enzyme is specific to, for example, starch) concentration. If you have a really "hot" malt that is full of amylase activity, you can use a lot of adjunct grains, like rice, because the malt has more than enough enzymes to get starch conversion completed in a set time. If you have a malt that is low in amylase activity, you may have a hard time converting the rice starch, even in a long mash.
The same holds true for proteases and glucanases - the duration of the rest depends on what you hope to accomplish, how much enzyme is present and how much substrate is present. One of the reasons I'm not a big believer in the protein rest is that there's not much protease activity after kilning and without proteases you don't have much chance for proteolysis.
Now onto foam. Foam is affected by numerous variables. It's most greatly affected by proteins, especially higher-molecular proteins and one low-molecular, weight-native protein called "Protein Z." It's also affected by carbon dioxide content, presence of fats and oils and, in the case of nitrogenated beers, dissolved nitrogen content. Certain beers bottled in clear glass use light-stable hop extracts that have their own foam properties, but these compounds are not widely available to the homebrew community.
I believe the key to producing a beer with a good foam is to keep adjuncts to a minimum, thoroughly rinse soapy cleaners from equipment, carbonate your beer enough to create a foam and use extremely clean glassware. The beers I brew with the best foam are my unfiltered wheats, using a portion of unmalted wheat, and my porter, which is nitrogenated. Unmalted wheat boosts the high molecular protein content and the nitrogen in the porter is the best weapon for creating a thick, creamy foam like draft Guinness. Long live beer foam!
Dear Mr. Wizard:
I bought some malt extract in 10-pound pails. I recently noticed that mold has developed on top of the malt. Has this ruined my extract or will the mold be eliminated in the boil? Can I scrape the top layer off and use what is left? Will refrigeration of the malt prevent mold? Please help!
Mr. Wizard replies:
Malt extract and damp malt will grow mold. Moldy grain certainly should not be used for brewing and I personally would not use malt extract with mold on the surface, though some brewers do. Removing the mold from the surface of the extract may completely remove the mold from the container but then again it may not. Mold is bad for two main reasons. Moldy grain is a known cause of gushing in beer. Certain molds, for example Fusarium species, excrete proteins that act as nucleation sites for carbon dioxide break-out in finished beer. In simple terms this means that when a bottle of beer is opened, the carbon dioxide uncontrollably breaks out of solution and a huge foamy mess gushes from the beer bottle. This is why it is called "gushing." The same thing could possibly result from using moldy malt extract.
Another reason to avoid using moldy malt or malt extract is that certain molds produce mycotoxins (toxins from mold) when they grow. Although many mycotoxins are completely destroyed when heated, some mycotoxins become more toxic when heated, as is the case with certain types of aflotoxin. This same concern applies to eating moldy foods. Not all molds are bad and some add a very nice flavor to food, such as Penicillium roqefortii that is used to make blue cheese.
The mold growing on your malt extract is most likely an airborne mold that came into contact with extract when you first opened it for use. Refrigeration will certainly slow the growth of mold and will extend the shelf-life of pails that are opened and only partially used. However, molds will grow in the refrigerator given enough time. Mold growth can be prevented on grains by storing grain in a dry environment.