Ask the Beer Fox - Astringency in Beer
Question: Concerning astringency in beer, you recommend removing the brown scum as it is formed, thus preventing it being stirred back in. Are you referring to the beginning of the boil? Where can I find additional info about this brown astringent scum? bucko, Brewtown, USA
Beer Fox Answer: No, when I refer to the “brown scum”, I am not referring to substances that form at the beginning of the boil, but to those formed in the initial stages of fermentation.
During the initial stages of fermentation a frothy substance forms on the surface of the wort. This is called kraeusen. The surface of this kraeusen is glazed with a bitter, brown, resiny scum. Some of this scum will adhere to the sides of the fermenter. After 3 to 6 days, this kraeusen falls back into the beer, and has the potential to add its bitter, tannic, astringent taste to the character of the beer.
If you use a closed fermentation system, with blow-out tube and glass carboy, this kraeusen is automatically removed during the initial stages of fermentation. When you remove this bitter resin, you will have gained the added benefit of diminishing the fusel oils that are a result of fermentation. These fusel oils are responsible for symptoms of "beer headache." If, however, you are using an open fermentation system, contamination can easily occur if you try to remove this scum, creating greater levels of off-flavors than if you had just allowed the kraeusen to settle back into the beer. Disturb the beer as little as possible so this scum remains undisturbed, and the flavors imparted to your beer will be minimal.
For further information, you can find a comprehensive list of books in the following article:
Homebrewing – Books & Resources – Novice to Expert
In particular, I would highly recommend Charlie Papazian’s book, The Complete Joy of Homebrewing, 3rd Edition. Among crafters of beer, it is regarded as the indispensable bible for homebrewers. Although Papazian started his career with a degree in Nuclear Engineering, he provides a down-to-earth explanation of the art and science of brewing in an easy to understand format, while adding advanced information as you gently glide into higher experience levels.
Question: Thanks for your quick response to my brown scum question. However, the brown scum that I am referring to forms at the beginning of the boil and if not removed it will dissolve into the wort inside of about ten or 15 minutes. I have heard that it is protein matter that has a lot of tannins in it and is very similar to the brown scum that appears on top of the yeast during fermentation. Does this brown scum that briefly appears at the beginning of the boil contain tannins that could be removed easier here than when they appear on top of the yeast during fermentation? bucko, Still Brewing in Brewtown, USA
Beer Fox Answer: Throughout the process of boiling and cooling beer wort, several physical/chemical reactions occur. At the beginning of the boil, foam forms on top of the wort. A brown scum quickly begins to accumulate on the surface of this foam, and within 10-15 minutes coagulated flakes begin to cloud the wort. These are the undesirable proteins and polyphenols that fall out of solution during a phase called the “hot break.” During this open, rolling boil, undesirable sulphur compounds, hop oils, ketones and esters evaporate; salts for correct boil pH are stabilized; bacteria, fungi and wild yeast are destroyed; enzymatic action halts; hop alpha acids are extracted, isomerized and dissolved in solution; some of the wort sugars caramelize; the stage is set for the formation of melanoidins; and wort is condensed to the proper volume and gravity, due to the significant evaporation of water vapor. A full, rolling boil helps with clarity, as well.
During the “cold break,” when the wort is rapidly cooled prior to pitching the yeast, more undesirable proteins coagulate and fall out of solution.
These materials collect as sediment and are known as trub (pronounced “troob”). Trub does not produce off-flavors, and always settles to the bottom. Its presence in homebrewing is not significant, although professionals and more-seasoned brewers may choose to remove this trub, either by more sophisticated filtering equipment, or by careful siphoning of the beer away from the trub in the transfer to the fermenter.
It is not necessary to scoop the scum and foam off the surface, as you suggest. Harsh tastes associated with tannins are extracted from grain husks during improper sparging. If you restrict sparging and exhibit close monitoring to adjust the pH to 5.7, you will avoid these unpleasant flavors. Avoid allowing the pH to rise above 6.0, although this may not be practicable if you are brewing a beer with high alcohol content.
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