Boiling
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The boiling process facilitates a number of functions:[1]
- the extraction and transformation of hop components
- formation of polyphenol-protein complexes
- production and removal of unwanted flavour compounds
- thermal destruction of cells
- thermal destruction of enzymes.
As reported by Levis and Young, wort is boiled in a wort boiling “kettle” to inactivate enzymes, remove undesirable flavor components, sterilize the wort, isomerize hop α-acids, and to precipitate haze-forming proteins and polyphenols.[2]
The hot break consists of protein (50–60%), bitter substances (16–20%), and other organic and inorganic substances, such as fatty acids and minerals. The hot-break content of the finished wort is between 400 and 800 mg/L (dry matter, extract-free), eg, 40–80 g dry trub or 200e400 g wet trub per hectoliter.[3]
Cold break can be separated at temperatures below 80°C when cooling down the hot break-free wort. Mainly, it comprises protein (48–57%), tanning agents (11–26%), and carbohydrates (20–36%).[3] Standard values are considered to be <70 mg/L (after Whirlpool) and <100 mg/L Kettle full (<85°C, before hops addition).
The boiled samples of wort from the brewery were the most intensely colored and the least were the barley worts. This finding confirms the importance of heat treatment in color development. Color is developed from the combination of phenols and phenol derivatives with sugars and proteins, through Maillard reactions.[4]
Wort boiling temperature and boiling time might be critical in determining the extent of the denaturing of LTP1 which was related to several beer quality traits such as beer foam, gushing and allergenic properties.[5]
Lengthy boiling could be detrimental to foam stability due to the reduced ability of denatured LTP1 to bind foam destabilizing lipids, particularly when the amount of lipids in the wort is high relative to the amount of LTP1.[6]
After the boil, coagulated proteins, hop particulates, and other insolubles should be removed from the wort before transfer to fermentation to prevent flavor stability, filtration, and yield issues. Trub has been shown to contain lipid levels over 51 times higher than the wort itself.[7]
Minimizing shearing of trub during pumping helps avoid excessive lipid content in the wort.[7] Minimizing foaming or splashing helps avoid lipid oxidation.
By modern standards, a modest 3–6% boil evaporation rate is common.[7]
Avoiding oxygen inclusion in the kettle during filling, heating, boiling, and transfer can minimize the autoxidation of lipids carried over during lautering. This means that splashing, foaming, and leaking pumps should be avoided.[7]
most of the reactions during wort boiling (e.g. trub formation) happen in the early stage of boiling.[8]
antioxidant activity level increases during wort boiling, likely because of the production of Maillard reaction products with antioxidant activity that are formed by the elevated temperatures during boiling.[9]
The degree of thermal solidification depends on the boiling time, which leads to a decrease in total phenolic content if the boiling time exceeds 60 min (Munoz-Insa, Gastl, & Becker, 2015).
- Munoz-Insa, Gastl, & Becker. (2015). Use of polyphenol-rich hop products to reduce sunstruck flavor in beer. Journal of the American Society of Brewing Chemists, 73, 228–235.
During wort boiling, the free wort Ferulic acid (FA) concentration increased by 10%. This net increase was the result of several factors. During wort boiling, thermal decarboxylation of FA will lead to the formation of 4VG. At the end of the boiling process, 0.14 ppm 4VG was found in the wort. This thermal decarboxylation caused the wort FA concentration to diminish by 9%. However, during wort boiling, the wort volume will decrease by 7–8% due to evaporation. This will cause an apparent increase in FA content. Finally, the addition of hop pellets will cause a real increase in wort FA content by 7–11% (based on results obtained in laboratory hop addition experiments). Taking into account these three factors, a net increase of the wort FA content during wort boiling will occur. The reassociation or coprecipitation of free FA with AX, polyphenols or proteins was negligible. Otherwise, no net increase in free FA content would occur during pilot-scale wort boiling. This was confirmed during laboratory-scale wort boiling experiments under reflux (no evaporation) without hop addition. During these experiments, the increase in 4VG corresponded with the decrease in FA.[10]
A whirlpool (extended settling time for hot wort) after boiling leads to lower antioxidant levels in the beer and a decreased flavor stability.[11]
Compared to commercial brewing, smaller scale brewing leads higher surface to volume ratio, which in turn increases oxygen uptake into the wort/beer, and also evaporation of volatile substances.[12]
Historically, a portion (1/3) of the calcium salt additive was added to the boil to ensure good clarity.[13]
Wort boiling diminishes the mineral concentration due to metals binding to the precipitated material. With the addition of hops, minerals are also added.[14]
- Thermodynamic Validation of Wort Boiling Systems
- Optimization of Wort Boiling by Process Reformulation and Design
- De novo Formation of Sesquiterpene Oxidation Products during Wort Boiling and Impact of the Kettle Hopping Regime on Sensory Characteristics of Pilot-Scale Lager Beers
- https://www.mdpi.com/1420-3049/14/3/1081/htm
- https://www.tandfonline.com/doi/full/10.1080/03610470.2020.1795782
- Impact of Different Wort Boiling Temperatures on the Beer Foam Stabilizing Properties of Lipid Transfer Protein 1
- Morikawa, M., Yasui, T., Ogawa, Y. and Ohkochi, M., Influence of wort boiling and wort clarification conditions on cardboard flavour in beer. Proceedings of the European Brewery Convention Congress, Dublin, Fachverlag Hans Carl: Nürnberg, 2003, pp. 775–782.
- Osamu, O., Imai, T., Ogawa, Y. and Ohkochi, M., Influence of wort boiling and wort clarification conditions on aging-relevant carbonyl compounds in beer. Tech. Q. Master Brew. Assoc. Am., 2006, 43(2), 121–126.
- Carpentier, B., van Haecht, J.L. and Dufour, J.P., Influence of the trub content of the pitching wort on yeast by-products synthesis. Proceedings of the Inst. Brew., Centr. & South African Sect., 1991, 3, 144–149.
- A New Validation of Relevant Substances for the Evaluation of Beer Aging Depending on the Employed Boiling System
- Release and Evaporation of Volatiles during Boiling of Unhopped Wort
- Protein precipitation during wort boiling: Quality aspects of diminished wort boiling times of brews prepared from proanthocyanidin-free or regular raw materials
- [BOOK] The influence of thermal load during wort boiling on the flavour stability of beer
Foam control agents see Handbook of Brewing 10.5 Clarifiers see 10.6 Boiling technology 11.9
No-boil[edit]
While neither barley limit dextrinase nor glucoamylase have strong activity during a typical mashing operation, there is evidence that these enzymes survive the mashing process and may be active during fermentation in a beer that wasn't boiled.[15][16] It has been suggested that limit dextrinase-inhibitor complexes could dissociate as the pH drops during fermentation, increasing its activity.[17] This will lead to additional degradation of dextrins and therefore a higher attenuation.
References[edit]
- ↑ https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.2010.tb00425.x
- ↑ Jin B, Li L, Liu GQ, Li B, Zhu YK, Liao LN. Structural changes of malt protein during boiling. Molecules. 2009;14(3):1081–1097.
- ↑ a b Pahl R, Meyer B, Biurrun R. Wort and Wort Quality Parameters. In: Bamforth CW, ed. Brewing Materials and Processes: A Practical Approach to Beer Excellence. Academic Press; 2016.
- ↑ Osman AM, Coverdale SM, Onley-Watson K, Bell D, Healy P. The gel filtration chromatographic-profiles of proteins and peptides of wort and beer: effects of processing—malting, mashing, kettle boiling, fermentation and filtering. J Inst Brew. 2003;109(1):41–50.
- ↑ Iimure T, Nankaku N, Kihara M, Yamada S, Sato K. Proteome analysis of the wort boiling process. Food Res Int. 2012;45(1):262–271.
- ↑ Evans DE, Bamforth CW. Beer foam: achieving a suitable head. In: Beer: A Quality Perspective. Academic Press; 2009:1−60.
- ↑ a b c d 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.
- ↑ Kühbeck F, Back W, Krottenthaler M. Influence of lauter turbidity on wort composition, fermentation performance and beer quality in large-scale trials. J Inst Brew. 2006;112(3):222–231.
- ↑ Pascoe HM, Ames JM, Chandra S. Critical stages of the brewing process for changes in antioxidant activity and levels of phenolic compounds in ale. J Am Soc Brew Chem. 2003;61(4):203–209.
- ↑ Vanbeneden N, Van Roey T, Willems F, Delvaux F, Delvaux FR. Release of phenolic flavor precursors during wort production: Influence of process parameters and grist composition on ferulic acid release during brewing. Food Chem. 2008;111(1):83–91.
- ↑ Uchida M, Ono M. Technological approach to improve beer flavor stability: analysis of the effect of brewing processes on beer flavor stability by the electron spin resonance method. J Am Soc Brew Chem. 2000;58(1):8–13.
- ↑ Biering J. Reliable scale up/scale down in process development—New possibilities to close the gap between lab, pilot brewery, and industrial scale. Slides presented at: Annual meeting of American Society of Brewing Chemists. June 4–7, 2017; Fort Myers, FL.
- ↑ Palmer J, Kaminski C. Water: A Comprehensive Guide for Brewers. Brewers Publications; 2013.
- ↑ Montanari L, Mayer H, Marconi O, Fantozzi P. Chapter 34: Minerals in beer. In: Preedy VR, ed. Beer in Health and Disease Prevention. Academic Press; 2009:359–365.
- ↑ Vriesekoop F, Rathband A, MacKinlay J, Bryce JH. The evolution of dextrins during the mashing and fermentation of all-malt whisky production. J Inst Brew. 2010;116(3):230–238.
- ↑ Walker JW, Bringhurst TA, Broadhead AL, Brosnan JM, Pearson SY. The survival of limit dextrinase during fermentation in the production of Scotch whisky. J Inst Brew. 2001;107(2):99–106.
- ↑ McCafferty CA, Jenkinson HR, Brosnan JM, Bryce JH. Limit dextrinase — Does its malt activity relate to its activity during brewing? J Inst Brew. 2004;110(4):284–296.