Haze Formation: Ways to induce or reduce its presence in beer
To understand haze formation prevalent in many beer styles, we must realize that one of the most common causes of haze is created by colloidal particles binding (joining) and cleaving (separating) due to their Brownian motion (this is described as the erratic and random movement of microscopic substances suspended in liquid). As these substances collide and form bonds, they can eventually form larger visible aggregates we call haze.
Turbidity is the way folks measure the level of haze; highly turbid liquids are more opaque while less turbid liquids are more clear. Factors that can have an impact on colloidal stability include protein molecular weight, temperature, oxidation, polyphenolic (tannin) concentration, light exposure, and acidity. The interaction of phenolic polymers (polyphenols) and certain proteins is a common source of many hazy beers and will be the focus of this piece as it is these interactions we observe in hefeweizens, kellerbiers, and hazy IPAs.
But just to make clear (no pun intended), there are several types of haze . . . some are desired and some not depending on the style of beer being produced. Too much residual starch from not properly mashing grains can cause haze, and bacterial infections can cause haze as well.
Another type that is familiar to most experienced brewers is chill haze. This is used to describe a haze that only appears when the beer is cold but then disappears when it is warmed up to room temperature. Chill haze happens due to loose, non-covalent bonds between medium molecular weight proteins and polyphenols. Although proteins and polyphenols are the primary constituents of chill haze, salts and metal ions are also bound up in haze particles.
Molecules vibrate rapidly at warmer temperatures, making it difficult for these protein-phenol bonds to remain intact. Thus the bonds are stronger at cooler temperatures; creating the chill haze phenomenon. The time it takes to form this haze can vary tremendously. In general, it usually appears two to three weeks after packaging. As time goes on chill haze can become permanent haze, which means that it does not dissolve at warmer temperatures as the non-covalent bonds turn into covalently bound haze particles.
Polyphenols and Proteins
Both malt and hops contain polyphenols and proteins. Polyphenols are polymers, or chains, of phenolic compounds (such as tannins, which can be derived from sources such as the husk of malt). The majority of the polyphenols found in beer come from cereal grains with hops typically contributing about 20%. Nearly all of the protein in beer also comes from the grains, with just a little contributed by hops and yeast suspension.
Malt modification has a large impact on the protein composition that makes it into the brewer’s wort. During the malting process, proteolytic enzymes reduce the size of malt proteins making the proteins (glutens commonly) less likely to precipitate out during the brewing process resulting in visible colloidal aggregates. In a study by Sofie A. Depraetere, F. Delvaux, S. Coghe, F.R. Delvaux published in the Journal of The Institute of Brewing, they compared nearly identical beers with the key differences being one beer used malt that had a longer germination time (more modified) and found that the beer made with higher modified malt had more permanent haze.
A key indicator for knowing how modified the malt may be is the Kolbach index. The more modified the malt is, the higher the Kolbach index reference will be. So the use of our modern, highly modified malts as a base malt in your hazy IPA or hefeweizen recipe may actually be helping induce haze thanks to the shorter and medium polypeptide/protein chains.
Digging deeper, let’s talk briefly about amino acids, which are the building blocks for peptides and proteins. Of these amino acids many are strong binders with polyphenols. Through the course of many studies, it appears one of the largest factors in colloidal induction is from a specific amino acid named proline, which has a strong ability to bind with polyphenols. The polyphenol flavan-3-ol and the amino acid proline attraction is a significant haze-forming interaction. The flavan-3-ol can come from both malts and hops, but beers with lots of late addition hops and dry hops will contain a high level of polyphenols. The hydrogen bonding between haze-active proteins and these polyphenols seems to occur at the proline site of the protein.
When the levels of polyphenols and proline-containing proteins found in suspension in beer are nearly equal, the beer is most inclined to be highly turbid. A heavy hand of end of boil hops and dry hopping can greatly assist to produce such results. Certain hop components such as beta acids are also known to be found in the haze particles, aiding in the formation of these large aggregates.
Wheat
Wheat berries contain high levels of protein. Even though the varieties of wheat chosen for wheat malts are selected because they contain lower protein levels than wheat selected for bread flour; relative to other cereal grains used in brewing they are still high. The higher protein levels combined with a lack of husk can contribute to haze but also decreased lauterability in the mash. The process of malting has an impact on the reaction of polyphenols and protein similar to barley in that it leads to lower molecular weight proteins. These medium-weight proteins and peptides are then more likely to stay suspended in the beer and have the capacity to interact with the polyphenols. In general, about 30% of proteins from the wort will find their way into the finished beer.
Malt modification has a large impact on the protein composition that makes it into the brewer’s wort.
Unmalted grains, however, have a different protein index. A study comparing beers made with malted wheat vs. unmalted wheat found that increasing the unmalted portion 20–40% yielded more clarity in the final product. There are a number of reasons this could occur, it is possible that the proteins (glutens) found in unmalted wheat will precipitate out earlier due to their large size. The same study also found that the higher the percentage of wheat vs. barley, the lower the number of polyphenols measured in the beer. This makes sense, as wheat does not have a husk, which is a rich source of polyphenols.
Oats, and other adjuncts
Oats are rich in proteins and soluble beta glucans, a carbohydrate that can produce turbidity. Other grains also contain beta glucans but oats happen to contain significantly more soluble forms than most brewing grains.
Even though there can be more total protein content in some of these grains, this doesn’t mean they will produce more haze. As mentioned previously, this depends on the molecular weight of these proteins, the types of proteins, and amino acid content. For instance, malted buckwheat and quinoa have much more total protein than malted barley but the protein contents of these are mainly albumins and globulins compared to that of malted barley whose main proteins are hordeins that contain much more of the amino acid proline. Because of this, grains like buckwheat and quinoa will produce less haze.
Hops, Polyphenols, and Yeast
As mentioned before, both hops and malt contain polyphenols. Polyphenol content in hops is rather low, averaging about 5% by weight, but when added in the dry hop stage, upwards of 50–60% of those polyphenols can make their way into beer. There does seem to be a connection with the varieties of higher alpha acid yielding lower polyphenol content, though there are some varieties that don’t fall in line with this. Coupling this with more recent popularity of heavy late-hopping schedules, it’s no surprise beers have become more and more hazy. Even though the total polyphenol content of hops isn’t immense, the increase of polyphenol addition can create a substantial enough reaction with the protein portion of the beer resulting in permanent haze.
Dry hopping early in a beer’s fermentation cycle has become popular in the production of modern hazy IPAs. This can have an effect on haze stability. A study conducted in 2013 by Berner, T., Jacobsen, S., and Arneborg, N. analyzed what happens to proteins during fermentation. Using two different ale strains (White Labs WLP001 California Ale and a European ale strain KVL011) it was found that protein content dropped during active fermentation with both yeast strains. The authors suggested this was likely due to enzymatic degradation of the proteins and/or proteins binding with yeast cells and subsequently flocculating out of suspension. WLP001 had a 16% percent decrease in total protein while KVL011 had a 42% decrease.
Dry hopping early, or before fermentation concludes, will allow more protein-polyphenol polymerization to occur before degradation and/or flocculation of the proteins during fermentation. Even though early dry hopping can create permanent haze, this occurs when the pH is out of the target range that is best for the binding process of polyphenols and proteins. A pH of around 4.2 has been shown to be the best for the induction of permanent haze. The pH affects the net charge of the proteins, in turn affecting how they bind. A study by Karl J. Siebert and P. Y. Lynn published by the American Society of Brewing Chemists found that a pH of 3.8–4.3 resulted in the highest turbidity.
Yeast decrease beer pH during active fermentation by absorbing basic ammonium ions and excreting organic acids. Reviewing the studies from above we can deduce dry hopping both early and late (not just one or the other) could yield the best colloidal stability.
Ways to Haze
While not groundbreaking news, the basic premise of these findings show that moderation in non-barley additions to the grain bill is good for inducing haze. 20% is probably a starting place, say 10% malted wheat and 10% flaked oats seems like a happy place for polyphenol, protein, and beta glucan contributions from the grain bill. The bulk of the remaining grain bill should be well-modified barley malt. If a large load of polyphenols from hops is not part of the recipe, as is the case with hefeweizens and wit beers, then there are clear exceptions to this rule.
If brewing a hazy IPA, then a healthy load of late boil or whirlpool hops, plus a two-stage dry hopping regime (one during active fermentation, the other after completion) is a great way of providing the necessary polyphenols and miscellaneous hop compounds to help induce a long-term haze in beer.
Ways to Unhaze
There are several ways to reduce haze in your beer. Keeping the protein count low is probably one of the easiest ways to do this, but polyphenols and beta glucans can also be mitigated. Fining your beer in both the kettle and fermenter is a common way for homebrewers to reduce haze.
Kettle-fining agents — Additives such as Irish moss and Whirlfloc behave in a different way than fermenter-finings such as gelatin or isinglass. Irish moss and Whirlfloc are rich in carrageenans (polysaccharides derived from seaweeds). These agents are added near the end of the boil and carry a positive charge. Meanwhile many proteins at a pH of 5–5.7 carry a negative charge. When adding these kettle finings to the boil they attract certain proteins, which will in turn increase cold break formation and help improve beer clarity.
Isinglass — Some proteins found in beer at <5 pH are positively charged and while collagen-based fining agents such as isinglass and gelatin have no effect on these ions by themselves, they do have an effect on protein-tannin reaction by slowing or inhibiting this interaction. An added benefit from isinglass is flocculation of yeast and tannins, which could lead to a less astringent beer.
PVPP — Polyvinylpolypyrrolidone is a fine powder that attracts and absorbs polyphenols including tannins. PVPP (also known as crospovidone) is mixed with cooled sterile water to form a slurry that is then added to the fermentation vessel. The slurry needs to be mixed thoroughly with the beer and allowed to settle out. The beer is then racked off of the sediment left at the bottom (or filtered out).
Clarity Ferm — Produced by DSM under the name Brewer’s Clarex®, White Labs Clarity Ferm contains an endoprotease that can reduce haze by hydrolyzing proline sequences in proteins/polypeptides. The enzyme does not select by size, rather by amino acid sequences. Proline is still able to bond haze-active polyphenols but the size of these chains alone are not large enough to cause turbidity.
Tanal B — A plant-based tannic acid that acts to absorb low weight proteins and encourages precipitation of these proteins. Tanal B is highly effective with proline-containing proteins but (according to the manufacturer, Wyeast) does not affect foam-positive proteins. This fining agent is used in the hot side of the brewing process.
Tanal A — Much like Tanal B, Tanal A is a plant-based agent. Though, it serves the opposite purpose. Tanal A encourages polymerization of tannin/protein reaction. This is meant to create permanent haze stability.
