|Yeasts about to begin fermentation requires a certain amount of oxygen to fuel some of its biochemical pathways.
This is notably for the production of unsaturated fatty acids and esters. It is normal practice to add oxygen to the
wort prior to fermentation; absence of sufficient oxygen will hamper yeast reproduction and can lead to disaster.
Historically aeration may have simply meant allowing the wort to cool in the presence of air by dropping the
wort into a fermentation vessel from above. Modern brewing practice dictates that oxygen be added directly
to the wort after it has been cooled.
Either filtered compressed air of oxygen from a cylinder is used and introduced into the flowing wort. The
solubility of the oxygen in wort is lower than in water because of the dissolved solids already in the wort.
The stronger the wort, the lower the solubility of the oxygen.
Calculating the amount of oxygen dissolved in the wort is possible but depends on the temperature of the wort
and the oxygen as well as their relative flow rates. Brewers will generally place a dissolved oxygen measuring
device downstream to achieve dissolved oxygen concentrations.
Bloom is a cloudy condition on the surface of glass bottles that can appear after a period of time, especially on
re-usable bottles that have been run several times through a washer and filler. Bloom is a chemical reaction and
part of the aging of glass. Technically, residual mobile ions, such as sodium ions, leach out of the silica sol and
react with ambient moisture. The newly formed sodium hydroxide, or lye, gradually dissolves the glossy outer layer
of the glass and turns it hazy. This may take months, but will not occur in dry and relatively cool environments.
There are various methods of removing bloom. Just washing a bottle with water can remove minor bloom, but
severe bloom requires a soaking for about five minutes in HCL and a subsequent rinse. To retard bloom, many
glass manufacturers apply a protective coating of sulfur, fluoride, or Freon compounds to their bottles.
Protein Rest is a period of enzyme activity during mashing when excess protein is removed and digested.
It is typically part of a series of temperature holds arranged in a sequence to ensure progressive digestion
of beta-glucans, proteins, and starches.
Not all mashes require a protein rest, but if poorly modified malt or high protein adjuncts are used, excess protein
is likely to be released into the wort, leading to possible hazes in finished beer. Removing protein from wort
involves both precipitation and enzyme digestion. A temperature of 119oF is optimal for these and results in the
removal of intact proteins in a precipitate and their breakdown into polypeptides and amino acids. This digestion is
most effectively achieved using natural protease enzymes derived from the barley malt. It has been suggested that
the term “protein rest” is a misnomer and that it should be called a “beta-glucan rest” because it is the breakdown
of beta-glucans by heat-sensitive beta-glucanases that is much more relevant at these lower temperatures.
Many brewers seek a middle ground between the optimum temperatures for peptidase and proteinase activity,
settling on a rest temperature of 122oF with the typical stand lasting from 10 to 20 minutes. Yet other brewers feel
that given today’s well-modified malts, the protein rest is an unnecessary anachronism. As in many other areas of
brewing, actual practice is often assembled from a blend of theory, observation, and tradition, with each brewer
deciding individually upon what he thinks works best for his beer and his brewing system.
Hope you found this month's column of interest. If you have any questions about beer or brewing
or just want to submit a word for me to discuss here just e-mail it to me.
Thanks and Cheers!
|Yeasts// Bloom // Protein Rest
|A new column by
|Jack O'Reilly attended the
famous Siebel Institute/ World
Brewing Academy in Chicago.
|I'm very excited to be part of the BeerNexus team. I think my many years in the
beer business both as a brewer and manger will enable me to explain and
investigate many topics of interest for those who really love craft beer.
Hope you join me every month.
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|Techniques and insights
for the serious ceft beer
fan and home brewer.