Trub
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During wort boiling and chilling, lipids, proteins, and other substances coagulate into solids call trub, making the wort cloudy. Denaturation of proteins renders them insoluble, as it exposes their hydrophobic regions, and lipids bind to this region because they are only partially soluble. Consequently, the trub contains a large amount of fatty acids, as much as 50–70% lipids by weight.[1][2] These lipids are undesirable in the wort because they contribute to the appearance of off-flavors during beer aging (see Lipids). Therefore, brewers should seek to transfer only clear wort to the fermentation vessel, leaving behind as much trub as possible. Trub formation ranges from 6,000 to 8,000 mg/L of wort, and after separation, 100 mg/L or less should remain in the wort.
Hot trub formation during wort boiling is mainly influenced by the release of intramolecular disulfide bonds by reduction to thiol groups and subsequent formation of new intermolecular disulfide bonds. This leads to coarser particles which eventually precipitate. Hot trub consists of proteins (40% to 70%), bitter substances (7% to 32%), organic substances (e. g., polyphenols) (20% to 30%) and ash (5%). The amount of hot trub formed depends on boiling time (Kuhbeck et al., 2006), which ¨ is in accordance with results by Munoz-Insa et al., where boiling ˜ times >60 min led to a decrease in polyphenol content. (i.e. greater phenolic precipitation)?[3]
In course of the brewing process, on average, 4.8% of the metals ions measured were found in the hot break and, thus, it made up the second biggest by-product for total metal ion release. Cu was found to be highest in concentration by far in the hot break (30.4%), which may be traced back to its affinity to bind to proteins (14). High losses of Cu in the hot trub were also reported by Zufall and Tyrell (52).[4]
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References[edit]
- ↑ Fix G. Principles of Brewing Science. 2nd ed. Brewers Publications; 1999.
- ↑ Golston AM. The impact of barley lipids on the brewing process and final beer quality: A mini-review. Tech Q Master Brew Assoc Am. 2021;58(1):43–51.
- ↑ Wannenmacher J, Gastl M, Becker T. Phenolic substances in beer: Structural diversity, reactive potential and relevance for brewing process and beer quality. Compr Rev Food Sci Food Saf. 2018;17(4):953–988.
- ↑ Wietstock PC, Kunz T, Waterkamp H, Methner FJ. Uptake and release of Ca, Cu, Fe, Mg, and Zn during beer production. J Am Soc Brew Chem. 2015;73(2):179–184.