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Myths vs. Facts:
Listed below are a few misconceptions conveyed to homebrewers.
Yeast Respiration
Myth: “Wort aeration is needed because yeast require oxygen for respiration”
Fact: Wort aeration is essential for the metabolism of the yeast and normal cell growth. The brewer should supply plentiful amounts of oxygen prior to fermentation for the metabolism to occur. Even when no oxygen is provided, many brewing yeast will ferment the wort, but this will result in a slow lag phase and the yeast will not be in good condition at the end of the fermentation. The oxygen provided by aerating the wort is not used to respire. It is used by the yeast to produce unsaturated fatty acids to make cell membranes. When an inadequate amount of oxygen is supplied, the membranes produced will be rigid and this will greatly affect transport of nutrients into the cell.
Protein Rest
Myth: “The protein rest is to create the nutrients required by the yeast to ferment the finished wort.”
Fact: Proteins are complex chains of amino-acid joined by peptide bonds. Proteins have a biochemical function in their native state. When the proteins are outside of their native state, the proteins is called a polypeptide or a denatured protein. There are few proteins in their native state found in malt since most are degraded during the kilning process. Proteins found in their native state in malt include for example, enzymes like alpha and beta amylases and beta glucanases.
Beta glucanases consist of several enzymes that break down various gums in barely and malt and are active during malting. However, because of their low resistance to increasing temperatures, they quickly denatured during mashing. Their activity in the mash can be increased by use of protein rest at a relatively low temperature. A better name for this is a “Beta glucanase rest”.
Hops
Myth: “Hop resins have a strong anti-microbial character.”
Fact: This myth is a little misleading as hop resins do have anti-microbial characteristics but these are limited. The iso-alpha-acids need to be in sufficient amount and a low pH for this claim to be true. Most beers today (lower hopped beers) do not have high enough levels of these resins for the anti-microbial characteristics to be effective. Furthermore, only gram positive bacteria are affected by the hops and, unfortunately, most bactria affecting the brewing process are resitant to the hop resins. It is true though, that boiling the wort and using hops will improve the microbiological stability of beer.
Microbial Infection
Myth: “Microbial infection destroys beer.”
Fact: It is very true that microbes can severly alter and change the flavors of beer to the effect that the beer tastes terrible. This, however, is not an infection but rather is a result of contamination. Infection denotes disease and the off flavors in the beer are not a result of the beer catching the flu. Refer to this as a contamination in the future.
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