Foam

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Beer is a complex mixture of surface-active compounds, which influence the presence of a stable and attractive head of foam in the consumer’s glass. The balance and interactions between these constituents of diverse chemical structures, such as proteinaceous components, polysaccharides, and hop acids, determine the beer foam quality including quantity, stability, lacing, density, and viscosity. It is commonly accepted that beer polypeptides with molecular weights of >5 kDa display great foaming potential. These polypeptides can be discriminated by their hydrophobicity or their viscosity.

Good foam formation and stability gives an impression of a freshly brewed and well-tasting beer. Beer foam is characterized by its stability, adherence to glass, and texture. Foam occurs on dispensing the beer as a result of the formation of CO2 bubbles released by the reduction in pressure. The CO2 bubbles collect surface-active materials as they rise. These surface-active substances have a low surface tension, this means that within limits they can increase their surface area and also, after the bubbles have risen, they form an elastic skin around the gas bubble. The greater the amount of dissolved CO2 the more foam is formed. But foam formation is not the same as foam stability. Foam is only stable in the presence of these surface-active substances. Beer foam is stabilized by the interaction between certain beer proteins, for example LTP1, and isomerized hop alpha-acids, but destabilized by lipids. The foam stability of proteins is increased by bitter acids derived from hops.

Foam-positive components such as hop acids, proteins, metal ions, gas composition (ratio of nitrogen to carbon dioxide), and gas level, generally improve foam, when increased. Whereas foam negatives, such as lipids, basic amino acids, ethanol, yeast protease activity, and excessive malt modification, decrease foam formation and stability. Free fatty acids, which are extracted during mashing, have a negative effect on foam stability.

the chemical–physical mechanisms through which proteins influence quality parameters are difficult to extrapolate, also because they depend on a series of additional factors. In fact, foam stability is also influenced by hop iso-α-acids, nonstarch polysaccharides, and metal ions.

Whereas the barley LTP1 does not display any foaming properties, the corresponding beer protein is surface active. Such an improvement is related to glycation by Maillard reactions on malting, acylation on mashing, and structural unfolding on boiling. LTP1 is claimed not to influence foam stability but the quantity of foam generated.

Proteinase A degrades LTP1 (but does not influence protein Z) and may have a negative influence on beer foam stability.

In its “foaming structure” LTP1 is susceptible to degradation by yeast proteinase A.

In their proteomic analysis of beer foam, Hao et al. (2006) detected practically all the main beer proteins, also including large fragments of hordeins, demonstrating that the protein interaction in foam can have a level of complexity higher than previously supposed (Kauffman et al., 1994; Kaverva et al., 2005).

Yeast thioredoxin is a possible foam-negative factor. There is conflicting information with regard to how yeast may affect foam-positive proteins.

The pleasant bitterness from hops concentrates in the foam as well as the aromas of hop oils, sweet corn (dimethyl sulfide), cardboard (oxidation), and spice aromas. Absence of foam accentuates malt, caramel, butterscotch (diacetyl), and fruity aromas. Consumers differ in the amount of foam they prefer, but they regard beer without foam or with rapidly collapsing foam as "flat."

The addition of most preparations of lipids to beer reduces head formation and survival. The effects are complex, both because different mixtures of lipids have different effects and because lipid binding proteins (such as LTP1, a 10 kDa albumin) can survive into beer and "mask" the effects of the lipids. Indeed, LTP1 constitutes a major proportion of the protein in foam. At least in some combinations, mixtures of different groups of lipids act synergistically to destroy foam when added experimentally to beer.

Lipid levels in beers made from clear wort are so low that their effects on foam are negligible.

An extended rest at 45°C is not recommended with well-modified malt since this always leads to poorer foam. Proteins that have a positive effect on foam originate from the hordein and glutelin fractions. The lipid transfer protein (LTP1) with 10kDa and the protein Z with 40kDa are particularly positive for foam. Their formation or release only occurs at temperatures above 60°C. However, poorly modified malt does require a protein rest. See Mashing.

Lactobacillus excretes proteases that degrade the proteins that cause foam.

Low pH directly degrades head retention.^{[citation needed]}

Magnesium sulfate affects foam?

Other studies have indicated that protein Z plays no major role in beer foam stability. In this study, normal malt, Z4-deficient malt, Z7-deficient malt and double-deficient malt were used in beer brewing, and no significant beer trait differences were detected among the four types of beer produced, indicating that protein Z is not significantly correlated with the foam stability of beer.

During the malting and brewing processes, LTP1 becomes a surface-active protein that concentrates in beer foam (10). In fact, the native barley seed nonspecific LTP1 (nsLTP1) displays poor foaming properties and becomes a foam-promoting agent only after unfolding on wort boiling. Because LTP is stabilized by disulfide bonds, reducing conditions (e.g. the presence of sulfites, but also possibly natural malt components) induce unfolding AND stabilize the foam-positive product.

Protein content in barley above 11% improves foam power, content below 9.5% reduces it.

Beer components (protein Z4, free amino nitrogen, b-glucan, arabinoxylan, and viscosity) are correlated with foam stability (evans et al, 1999).

Iimura et al. correlated proteins identified by 2-DE with beer foam stability across different cultivars and different modification conditions. They identified three protein ’spots’ that correlate with foam stability. They extended these findings and their general applicability by showing that one was protein Z from barley and another was yeast thioredoxin. The third was barley dimeric a-amylase inhibitor-1 (BDAI-1). Both BDAI-1 and protein Z were foam-positive factors. However, yeast thioredoxin was reported as a novel foam-negative factor, so there emerges a more comprehensive and collective view of foam stability.

The quantity and stability of beer foam indicates that the beer is fresh, pleasing to behold and properly carbonated, while consumers judge that beer that displays haze as not being fresh or stale.

Protein Z4 and protein Z7 are positively and negatively correlated with beer foam stability, respectively. Barley lipid transfer protein 1 (LTP1) is another factor associated with beer foam stability.

Proteins are essential in the foaming properties of a beer in forming a visco-elastic film around gas bubbles. Other components can infl uence the formation and stability of beer foam. For example, ethanol improves foam formation but decreases its stability. Hop acids increase foam stability in forming complexes with protein at the gas–liquid interface. Lipids are the main foam-negative substance of beer. These hydrophobic and/or amphiphilic molecules adsorb rapidly at the interface and destabilize the protein film by displacing protein and decreasing protein–protein interactions. This leads to the rupture and coalescence of foam bubbles.

Lipids and especially FFAs are detrimental to the formation and stability of beer foam. Trapping of the major barley FFA (i.e. linoleic acid) by LTP1 through the combined activity of LOX and AOS should limit the accumulation of the foam-destabilizing FFAs. This mechanism could act synergistically with the non-covalent lipid binding to protect beer against lipid-induced foam destabilization. Finally, it should be emphasized that the quality of beer foam is not due to a unique protein but to complex associations between the different beer proteins and between proteins and other components (phenolic compounds, hop acids, minerals, etc.) as well as to the technological process (i.e. malting and brewing) that induce different structural modifications essential to generate pro-foaming entities.

LTP1 is modified during wort boiling, and promotes foam stability (Sorensen et al., 1993). On the other hand, van Nierop, Evans, Axcell, Cantrell, and Rautenbach (2004) showed that modified LTP1 does not properly bind to foam negative lipids. They also suggested that wort boiling temperature was a key factor controlling LTP1 modification in beer, since the basic isoelectric point of intact LTP1 is modified during wort boiling by the Maillard reaction, and the resulting glycated LTP1 has an acidic isoelectric point (Hippeli & Hecht, 2009; Jégou, Douliez, Mollé, Boivin, & Marion, 2000). The modification of protein Z, glycation and partial digestion, has been well studied. Protein Z is glycated in the malting process by the Maillard reaction and the resulting glycated protein Z affects beer foam stability (Curioni, Pressi, Furegon, & Dal Belin Peruffo, 1995).

It has been demonstrated that LTP1, which is modified during wort boiling, promotes foam formation (Sorensen et al., 1993). van Nierop et al. (2004) showed that intact LTP1 contributes to foam stability because it binds to foam negative lipids. They showed that wort boiling temperature was critical in determining beer LTP1 content and conformation. Hippeli and Hecht (2009) and Jégou et al. (2000) suggested that the basic amino acid residues of LTP1, such as lysine and arginine react with reducing sugars through a Maillard reaction, to produce glycated LTP1, and that the isoelectric point of LTP1 shifts to acidic. The results of the present research showed that the spot intensities of LTP1 with a basic pI in the boiled wort were lower than that in the sweet wort (Fig. 2). In the current sweet wort proteome map, LTP1 was only identified in the basic pI range (6.92–8.58) (Fig. 6). On the other hand, LTP1 in beer was identified in a broad range of pIs (4.36–8.37) (Iimure et al., 2010). Therefore, our data supported the suggestion of Hippeli and Hecht (2009).

This LTP1 form concentrates in beer foams to contribute widely to foam formation, whereas foam stability depends on protein Z. The structural and chemical modifications of the two proteins during the brewing process may explain their foaming potential in beer. In fact, protein Z displays different isoforms with acidic pI (6) further to its glycation during processing through the Maillard reaction (9). Recently, it has also been shown that beer LTP1 is glycated, probably by Maillard reaction that occurs on malting (17, 18). Glycation might prevent protein from precipitation on unfolding during the wort boiling step. Both glycation and denaturation should increase the amphiphilicity of LTP1 polypeptides and then contribute to a better adsorption at air-water interfaces of beer foam. However, it is noteworthy that a significant part of the beer LTP1 is not denatured and could prevent beer foam destabilization by lipids.

Boiling wort for a longer time leads to decreasing foam stability, possibly due to removal of Protein Z, which slowly binds with other proteins and precipitates.

Using proteome analysis, Iimure et al. (2008, 2009) identified additional beer foam proteins (BDAI-1 and yeast thioredoxin) and haze active proteins (BDAI-1, CMb and CMe).

In the presence of sulfite, lipid adduction increased significantly the thermal stability of LTP1, whereas glycation has no or only a slight effect on the structural stability. Therefore, whatever LTP1 modification, lipid adduction or glycation, heating and reducing environment act synergistically on LTP unfolding. (Glycation, lipid adduction, and unfolding observed on malting and brewing, in this work and in previous studies (9, 17), should contribute to the transformation of barley LTP1 from a poor foaming to a foam-promoting protein.)

The malting and brewing process transforms the barley albumins into foaming proteins. The mechanism involved in these structural maturation has been recently delineated, especially for one of the major beer proteins, LTP1. Actually, the barley LTP1 does not form any foam while the corresponding beer protein display good foaming properties. In beer, LTP1 is a mixture of glycated proteins displaying different unfolding state. Glycation occurs on kilning during the malting process while unfolding occurs on brewing. Heat-induced unfolding of LTP1 is strengthened by the reduction of disulfi de bonds of the protein during the extraction of malt. The disulfide bond reducing mechanism of malt has not been identified yet, but it should involve the thioredoxin and/or glutathione oxido-reducing pathways. The other important modifi cation is the acylation of LTP1. This acylation is catalyzed by two enzymes from the embryo, a 9-lipoxygenase (9-LOX) and an allene oxide synthase (AOS). 9-LOX generates a 9-hydroperoxide from linoleic acid, the major polyunsaturated free fatty acids (FFAs) from cereal seeds while the AOS transforms the hydroperoxide in the corresponding allene oxide. The electrophilic attack of the unstable allene oxide by an acidic side chain of the protein (Asp7) leads to the covalent binding of an alpha-ketol to LTP1. This acylation has been observed in beer for the glycated LTP1. Up to two alpha-ketol can be covalently bound to the barley LTP1. Finally, glycation and acylation increase the amphiphilic character of the protein while unfolding improves spreading of the protein at the air–water interface allowing a better anchoring in the interface through the acyl adducts and formation of protein–protein interaction in the film surrounding gas bubbles.

LTP1 would appear to have different modes of action in relation to beer foam quality. Firstly in isolation, beer LTP1 has excellent foam generation but poor foam stabilizing properties. The foam stabilizing properties are substantially enhanced when it is combined with an isolated LMW hordein/glutelin or HMW foam fraction that contains protein Z (Sorensen et al., 1993). This efficacy with other proteins to provide foam stability was also observed by Douma et al. (1997). Bech et al. (1995a,b) found that increasing the beer LTP1 content resulted in improvements in foam stability when foam performance was assessed by a digital analysis system that was the fore-runner to the Lg automatic tester. Similarly Lusk et al. (1995) also concluded that LTP1 was an important determinant of foam stability as judged by the Constant foam analysis test. Conversely, small scale (600–800 ml) and pilot (50l) trials that primarily used the Rudin foam analysis procedure found an ambiguous relationship between LTP1 and foam stability with different trials showing positive, negative or no correlation (Evans et al., 1999c, 2003). In part the explanation for these observations might be that the Rudin analysis measures foam stability and takes no account of the amount of foam formed. Alternatively, the second mode of action of LTP1, as a lipid binding protein may explain the discrepancies outlined above. Van Nierop et al. (2004) observed that increased denaturation of LTP1 by boiling could in fact be detrimental to foam stability due to the reduced ability of denatured LTP1 to bind foam destabilizing lipids. Where the level of lipids in beer was low or the level of LTP1 was high there was little impact on beer foam stability, however where the level in beer of LTP1 was low, and the level of lipids high, substantial reductions in foam stability were observed (Table 1.2).

Leiper et al. studied beer proteins that are involved in haze and foam formation. All proteins were found to be glycosylated to varying degrees. The size range of the polypeptides which make up the glycoprotein fraction of beer is relatively narrow and the range was found to be from 10 to 46 kDa. The glycoproteins were found to consist of proteins, six carbon sugars (hexoses), and five carbon sugars (pentoses). Beer glycoproteins were found to exist in three forms; those responsible for causing haze, those responsible for providing foam stability, and a third group that appeared to have no role in physical or foam stability. Approximately 25% of beer glycoproteins are involved in foam and foam stability. As 3–7% of beer glycoproteins have been identified as being involved in haze formation, this leaves around 70% of beer glycoproteins that appear to have no role in either physical and/or foam stability. This fraction contains the most abundant beer polypeptide, protein Z, which is glycosylated with both hexoses and pentoses. It has been estimated that about 16 % of the lysine content of protein Z are glycated during the brewing process through Maillard reaction.

Degradation of beer ns-LTP1 by yeast proteinase A (released by autolysis from dead yeast cells) causes a decrease in beer foam stability during beer storage10. Activity of proteinase A could be reduced by application of low proteinase A activity yeast strains, low fermentation and maturation temperatures, and fast yeast separation after fermentation. The employment of high gravity brewing negatively influences foam promoting protein levels142.

The components that influence foam stability include proteins, substances from hops, metalions and polysaccharides. cites:

• Iimure T, Nankami N, Sirota N, Transu Z, Hoki T, Kihara M, Hayashi K, Kazutoshi I, Sato K (2010) Food Chem 118:566–574
• Evans DE, Sheehan MC (2002) J Am Soc Brew Chem 60:47–57

While over 99.5% of barley lipids are lost throughout the brewing process (Fig. 8), those that do survive can negatively impact foam stability, even at low levels. Specialty malts that are intensely heated during production can inhibit foaming when included in the grain bill, such as crystal 75L (Lovibond). This appears to be a result of the elevated levels of TAGs and lipid hydroperoxides in the wort due to the inclusion of these malts. Beers brewed with LOX-less malts in the grist bill saw improved foam stability.

Other potential sources of lipids that can negatively impact foam stability are poor glassware washing or lubricant inclusion (11).

The stability of beer foam is mostly due to hydrophobic interactions between a variety of species including polypeptides, polysaccharides, iso-α-acids and lipids, whereas competing surfactants and chaotropic agents (e.g., ethanol, magnesium chloride) disrupt this stability [38,43].

The addition of hop extract resulted in a negative effect on foam formation. This can be explained by the specific type of hop α-acids present in the applied hop extracts, possibly having a negative effect on foam formation.

The lower stability in the beer sample with higher amount of Caraamber malt can be explained by its higher content of nitrogen compounds (amino acids and oligopeptides) obtained during roasting of malt, that when in higher concentrations, are able to banish polypeptides from the film of gas bubbles, decreasing foam stability (Gresser 2009).

Both foam retention and lacing have been found to be influenced by longer chain fatty acids, with shorter chain fatty acids (C10 and shorter) having little effect. Concentrations of the individual long chain fatty acids in wort are invariably too low to influence foam in a significant way. However, the combined action of several long chain fatty acids could conceivably have an observable effect. It has also been found that if foam negative lipids are introduced to wort, their effect is temporally limited and, given enough time, the detrimental effect of these lipids will be negated, probably via interaction with lipid-binding proteins. The use of immobilized lipid-binding protein has been shown to improve the foam stability of a number of commercial beers and the different susceptibilities of different beers to the effects of lipids on foam may be related to the relative content of lipid-binding proteins in the respective beers. Lipid-binding proteins derived from wheat have been found to improve the foam stability of beers and this may, to an extent, explain the superior foaming characteristics of wheat beers relative to all-malt lager beers. It may be the case that other foam-negative factors introduced at the point of dispense (e.g., detergents) or during drinking (e.g., cosmetics or foods) will have a greater influence on foam characteristics than either malt- or yeast-derived fatty acids.

Lipids may in fact have a positive effect on foam character. For example, basic amino acids have been identified as foam negative factors by Furukubo et al.74, a result which the authors ascribed to a possible interaction between the amino acids and foam positive iso-α-acids. It would be expected that this negative effect would be mitigated through the increased amino nitrogen uptake associated with turbid or UFA-supplemented wort196. High ethanol concentrations may indirectly decrease foam stability by causing release of proteinase A during fermentation29. This enzyme may persist in the beer and have a negative effect on foaming potential by interfering with foam-stabilizing proteins29. The influence of maltderived lipids on foam may in some cases be negative124,186 and in others neutral111.

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• Robinson LH et al (2004) The interaction between malt protein quality and brewing conditions and their impact on beer colloidal stability. Tech Q MBAA Communicator 41(4):353–362 "oxygen during the brewing process influences haze stability of beer"
• Bamforth, C. (2004). The relative significance of physics and chemistry for beer foam excellence: Theory and practice. Journal of the Institute of Brewing, 110(4), 259–266.
• Evans, D. E., Sheehan, M., & Stewart, D. (1999). The impact of malt derived proteins on beer foam quality. Part II: The influence of malt foam-positive proteins and non-starch polysaccharides on beer foam quality. Journal of the Institute of Brewing, 105(3), 171–178.
• http://www.themodernbrewhouse.com/uncategorized/foam/
• http://www.themodernbrewhouse.com/wp-content/uploads/2020/06/32_6.pdf
• Mathematical modeling of beer foam.
• Impact of different wort boiling temperatures on the beer foam stabilizing properties of lipid transfer protein 1.
• Application of ELISA to Quantitative Evaluation of Foam-Active Protein in the Malting and Brewing Processes.
• Don't Be Fobbed Off: The Substance of Beer Foam—A Review
• Chapter 10 - Controlling Beer Foam and Gushing
• https://books.google.com/books?hl=en&lr=&id=2UqCFxskEnMC&oi=fnd&pg=PA1&dq=info:njv25IasXREJ:scholar.google.com/&ots=fmdhu5z8UU&sig=_xZ_QieDgvYf8LaNMG9qcmMoD4I#v=onepage&q&f=false
• Recent discoveries in beer foam.
• The foaming properties of beer
• Degradation of a foam‐promoting barley protein by a proteinase from brewing yeast
• The release of yeast proteolytic enzymes into beer
• An immunochemical analysis of beer foam
• Assessment of beer foam stability by high performance liquid immunoaffinity chromatography (HPLIAC)
• see Handbook of Brewing 10.9
• https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.1999.tb00016.x
• https://www.mbaa.com/publications/tq/tqPastIssues/1989/Abstracts/tq89ab25.htm
• Ishibashi Y et al (1997) Application of ELISA to quantitative evaluation of foam-active protein in the malting and brewing processes. J Am Soc Brew Chem 55(1):20–23
• Hydrocolloids as beers foam stabilizer
• Gupta, M., Abu-Ghannam, N., and Gallaghar, E. 2010. Barley for brewing: Characteristic changes during malting, brewing and applications of its by-products. Compr. Rev. Food Sci. Food Saf. 9:318-328.
• D. Evan Evans, Charles W. Bamforth. Beer foam: achieving a suitable head. 2009,,, 1-60. https://doi.org/10.1016/B978-0-12-669201-3.00001-4
• Iimure, T., Kimura, T., Araki, S., Kihara, M., Sato, M., Yamada, S., Shiryou, T., Sato, K., 2012b. Mutation analysis of barley malt protein Z4 and protein Z7 on beer foam stability. J. Agric. Food Chem. 60, 1548–1554.
• Malt derived proteins: Effect of protein Z on beer foam stability
• Degradation of a Foam-Promoting Barley Protein by a Proteinase from Brewing Yeast
• Circular dichroism and infrared spectroscopic characterization of secondary structure components of protein Z during mashing and boiling processes
• Role of Beer Lipid-Binding Proteins in Preventing Lipid Destabilization of Foam
• Destabilization of beer foam by lipids: Structural and interfacial effects
• Prediction of Beer Foam Stability from Malt Components
• Lewis, M.J.; Lewis, A.S. Correlation of beer foam with other beer properties. Tech. Q. Master Brew. Assoc. Am. 2003, 40, 114–124.
• Evans, D. E., Finn, J. E. C., Robinson, L. H., Eglinton, J. K., Sheehy, M., and Stewart, D. C. (2011) The effects of hop-α-acids and proline-specific endoprotease (PSEP) treatments on the foam quality of beer, J. Inst. Brew. 117, 335–342.
• https://onlinelibrary.wiley.com/doi/full/10.1002/jib.594