Lesson 2 - Beer Foam
In this lesson we will discuss the physics and mechanics of foam formation and collapse, along with the chemistry of the compounds involved with beer foam.
Foam is affected by the brewing of raw materials and by wort and beer processing within and outside the brewery. The measuring of foam will be discussed and we will end the lesson by looking at gushing.
Wort Production Influences on Foam
In the brewhouse, several factors can affect foam stability. In brewing, processing aspects that favour one aspect may be detrimental to another. This is especially true in the brewhouse area.
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High gravity brewing – this is negative to foam potential due to:
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A proportionally higher loss of foam protein
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Protease excretion as a yeast stress product
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The destabilising effect of higher ethanol content.
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If adjuncts are used, these will further reduce foam stabilising protein.
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Exogenous enzymes – their use might lower foam stability if a preparation, such as β-glucanase, contains traces of protease (which will hydrolyse foam protein).
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Mash temperature – a low mash proteolytic stand at 50 °C would favour proteolysis and breakdown of the foam proteins. At this temperature, increased activity of lipoxygenase enzyme would be experienced with associated increases in oxidised lipids, which are known to be foam-negative.
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Wort separation – the device and its operation will affect lipid carryover. Older mash filter designs produced higher levels of fatty acids than a lauter tun; however, modern mash filters produce less lipid carryover than lauter tuns. The running of worts to a gravity that is too low, encourages polyphenol extraction from malt husks, which in turn will bind and remove protein.
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Wort boiling – this is a key step for foam stability in the brewhouse. Like many aspects in brewing, boiling is a compromise; on the one hand, we need a vigorous boil to concentrate the wort, drive off volatiles and precipitate unwanted haze forming proteins, polyphenols and lipids. On the other hand, we want to preserve foam-positive factors. Let us try to summarise some of the key concepts here:
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Heating wort to boiling point denatures and rearranges LTP1 protein, activating it as a foam stabilising protein.
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Excessive boiling will, however, precipitate the foam-positive proteins, which are also lost in foam sticking to the kettle surfaces in an overly vigorous boil.
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Boiling extracts and isomerises the hop α-acids, which are beneficial to foam.
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Foam-negative lipid material is precipitated with the trub.
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Maillard reactions take place, forming carbohydrate-protein products that are associated with improving foam-positive proteins.
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Post-boiling wort clarification effectiveness will affect wort lipids levels. Cloudy worts contain higher levels of foam-negative lipids and a surplus that is not removed by yeast would persist into the final beer – this would produce foam-negative effects.
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