Colloidal Brew
CE 547
4/4/00
Larry Heverley III
Joseph Leonard
Laura Rusinski
Carol Schuster
Abstract
Colloids in beer contribute to beer haze and premature shelf-life of the product. Methods
to minimize, and in some cases, eliminate, the formation of colloidal particles such as proteins
and polyphenols have been developed since beer production began, and those methods are
continuously improving today. In addition, the methods of detecting beer haze in the form of
colloidal particles have been implemented and improved. This paper focuses on these various
techniques and their applications to colloid removal in beer.
Introduction
As has become evident through this course, colloids are an integral part of everyday life.
From dairy products to cosmetics, colloids are everywhere. This pervasive nature is even present
in a staple of student life everywhere: beer!
In this case however, colloids tend to be negative byproducts to be avoided. Have you
ever gazed into a glass of beer that didn’t quite taste right, only to notice it was cloudy? It is this
unpleasant perturbation of what should be a crystal clear brew that is itself a colloidal suspension
known in brewing jargon as ‘beer haze’.
The appearance of beer is a very important factor especially for consumers. The level of
beer clarity, or more appropriately the lack thereof (haze), can be determined by transmission
and scattering characteristics.
Experiments have shown that high concentrations of small
particles (<500 nm), including yeast, Kieselguhr (diatomaceous earth), bacteria, fining agent,
polyvinylpyrrolidine (PVP), and protein-size particles present in “rough beer” are the major
contributions to formation of larger haze after filtration. Based on this fact, we would like to be
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able to measure these small particles. Particle size information has potential value in these
areas2:

Detection of fine hazes that may become visible in later processes, and therefore requires
corrective action.

Predicting shelf life, which can be shortened by a high concentration of haze.

Monitoring overall performance of the filter.

Predicting filterability.
The objective of filtration is not only to remove suspended materials that give the hazy
appearance, but also to remove oligomeric materials that can further polymerize causing haze
formation and sedimentation while on the store shelf.
Procedure for Beer Production
All beer production follows the same, general format.
Beer begins with a process
“mashing,” or simply combining and crushing all of its starting products together. Next comes
fermentation, whereby the starting products such as various yeasts are fermented either
aerobically or anaerobically to allow both flavor and alcohol content to be present in the final
product. Once fermentation is complete, the post-fermentation period begins. Here, the beer is
very close to its final state, as only a few beneficial additives are combined with the basic
mixture following the initial steps. Once this is complete, the beer needs only to be packaged
and placed on the shelf, but it is before this can occur that it is crucial to detect the beer’s level of
haze and determine whether or not it is acceptable.
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Methods for Haze Detection
A quick check on the clarity can be done using “shadow box”. This is a lab instrument
used in most breweries for visual estimation of haze. For continuous clarity measurement during
the process, a 90-degree-angle measurement of radiometer hazemeter is used, as well as a small
angle measurement called forward scatter. Both measurements give particle size information.
Simultaneous measurement is used to compare the response of each technique.
The apparatus for a simultaneous measurement is set up as follows. A polychromatic
light source is used to illuminate a three-inch diameter flow cell. A detector unit measures the
light scattered at 90 degrees and a non-imaging optics sensor collects the light scattered at the
short (13) angle. A transmitted light signal is used to adjust the detector to the wavelengths of
interest. This eliminates the ‘beer color’ effect that can cause error in the hazemeter reading. The
combined instrument alleviates weaknesses in the individual sensors. For example, the forward
scatter (13) sensor has decreasing sensitivity as the particle size becomes smaller and the 90degree scatter sensitivity decreases with an increase in particle size.
With this technology available, beer haze has become a well-defined quality control
concern. Beer haze is one of a few quality considerations referred to by the phrase ‘colloidal
stability’, which indicates the likelihood that a beer will not develop a haze or an unpleasant
flavor. The issue of colloidal stability has become more important in recent years because of the
more increase in export of packaged beers as more international markets have become available.
Currently, a beer is expected to retain its colloidal stability for 12 months. With this in mind, a
lot of research has been done on enhancing colloidal stability of beer.
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Types of Haze
In general, there are two main categories of beer hazes: biological and non-biological.
Biological hazes are caused by infection of the brew with wild yeasts or bacteria. Such hazes are
caused almost exclusively by poor hygiene during processing.
They are irreversible, and
therefore the batch must be discarded. In the arena of non-biological hazes, there are a few
different causes. Organic components such as oxalic acid can occasionally give rise to “green
haze” which is a suspension of calcium oxalate. This is usually not a problem since calcium
oxalate usually separates from beer during fermentation and storage. Inorganic components such
as iron and copper ions can complex with other brew components to cause a haze, however this
can usually be avoided by using stainless or plastic containers.
The third, and by far most important non-biological cause of beer haze is
protein/polyphenol interactions. Both proteins and polyphenols occur naturally in the grains that
beer is made from. The exact chemical mechanism of how these two beer constituents react is
not known. In general though, the hydrophilic characteristic of proteins and the hydrophobic
characteristic of polyphenols combine to form surfactant-like molecules.
In sufficient
concentrations (C>CMC) these molecules form a polydispurse suspension of micelles that cause
a hazy look in the beer. There are a couple main ways of avoiding this type of haze.
How to Avoid Beer Haze
The first way is to avoid two things that are known to catalyze the reaction between the
proteins and polyphenols: oxygen and high temperature. Avoiding high temperature is rather
self-explanatory, but there are a couple methods of minimizing oxygen exposure that should be
mentioned. First, the entire brewing system should be purged with an inert gas such as carbon
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dioxide or nitrogen before brewing is to begin. Oxygen will spoil a beer almost as fast as it will
spoil an inorganic reaction.
A second way of avoiding oxygen is to minimize container
headspace in packaging. Over the past 75 years in the USA, beer bottle head spaced has dropped
from 9.4mL to 0.9mL.
Another way of avoiding hazes caused by proteins/polyphenol interactions is to minimize
the concentrations of either one or both of those components. This requires an understanding of
what causes production of proteins and polyphenols, what their properties are, and which are the
best methods for their elimination.
Polyphenols
Polyphenols, which are also commonly known as “tannins5,” are an important factor in
terms of the colloidal stability of beer. There are three basic classes of polyphenols that affect
beer production, the first being the simple polyphenols. Derived from hydrobenzoic acid and
hydroxycinnamic acids, these polyphenols are extracted mostly from malt. Flavanols, the second
class of polyphenols, have a more complex structure than the simple polyphenols and are derived
mainly from hops. The third class of polyphenols includes proanthocyanidins, their derivatives
the anthocyanogens, and catechins. This third class is comprised of monomeric polyphenols,
which have little effect on haze formation until they combine to form dimers, trimers, and so
forth. These molecules result equally from both malt and hops, and make good targets for
elimination from the beer mixture5.
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Polyphenol Removal
In terms of the removal of these polyphenols, there are different methods that can be
utilized with regard to each stage of brewing. For example, when initially selecting the materials
for brewing, it has been proven that use of barley (ANT-13), which has lower polyphenol content
than most barley, results in an overall higher colloidal stability of beer5.
Once appropriate materials are selected for optimum polyphenol avoidance, it is possible
to add certain components to counter the effects of polyphenol formation. This is seen in the
utilization of the “haze index,” a measure of the ratio of polyphenols to alpha acid content. The
typical range of this index shows values of 0.15 to 1.71, with acceptable colloidal stability
resulting in a value less than 0.45. In other words, it is possible to increase the alpha acid
content, causing a decrease in polyphenol formation, and resulting in higher colloidal stability.
It is difficult to quantify the effect of the fermentation process in polyphenol removal.
While there is proof that yeast is useful in absorbing proanthocyanidins, it is not clear the effects
of temperature, duration, or procedure on this ascertainment. At any rate, fermentation is helpful
in the removal of certain polyphenols.
When beer is in the mashing process, there are also techniques to decrease the presence
of polyphenols. Addition of 1000 ppm of formaldehyde, with respect to the malt, causes an 84.8
percent decrease in the measured amounts of anthocyanogens and proanthocyanidins, and an
overall five-fold increase in colloidal stability by approximation5.
The post-fermentation period also can be used with further procedures for polyphenol
removal.
The addition of various components in this stage can prove very effective for
extraction of these molecules that formed undesirably within the previous stages of beer
production.
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One additive with this capability is STABIFIX Brauerei-Technik. This material contains
silica gels that, when added to beer, result in absorption and subsequent removal of polyphenols
through filtration or sedimentation6.
Another additive of choice is polyvinylpyrrolidine (PVP or PVPP), a high molecular
weight, synthetically derived polymer. PVP specifically absorbs polyphenols and can be filtered
out in standard filtering procedures. When insoluble PVP is added, it is more effective than
soluble PVP. As an example of this, 91 to 93% of proanthocyanidins were removed by the
addition of 12 g/hl of Polyclar AT5. However, the effectiveness of this additive is decreased with
increasing amounts of yeast present in the mix.
Polyamide resins are also of interest for polyphenol removal, due to their ability to adsorb
to anthocyanogens. This requires using between 1 and 20 g/l of insoluble polyamide resins, and
a contact time of at least 24 hours, and is generally quite effective in instilling colloidal stability5.
Unfortunately, it is very difficult to recover the resins from the mix once the process is
completed, which is a major disadvantage in utilizing this method.
Proteins
Aside from polyphenols, a major non-biological component of beer haze is proteins,
which are usually acidic and hydrophilic in nature. Most protein constituents in beer haze are a
by-product of the barley in the mashing stage.
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Protein Removal
The two most common additives used to remove protein hazes are silica hydrogels and
bentonite clay. They are added to the process after fermentation where they adsorb protein
molecules, forming flocs, which settle to the bottom of the vessel.
Silica hydrogels [H2Si2O5], are polymeric materials produced from an acid-silicate
solution. After polymerization, they are separated from the solvent, dried and milled to a fine
powder. The product is able to adsorb high molecular weight proteins when added to the beer.
Although silica additives are highly effective in clearing haze from beer, it can be somewhat
expensive.
Bentonite [(Si4O10)(Al(OH)2).nH2O] is a naturally occurring clay but is processed to
optimize its effectiveness in beer clarification. This process involves and acid solution of the
clay in which metals in the molecular structure are dissolved. The clay is then washed dried and
milled to a powder. The dissolved metals leave a charged interstitial area to which proteins in
the beer haze are attracted, forming flocs that settle to the bottom of the process tank. Bentonite
additives are able to adsorb 5 to 6 times their weight of water while losing only one to three
percent of the beer. They have the added advantage of being reasonably priced.
While it is necessary to remove both proteins and polyphenols, the removal of only one
of the components individually can result in flavor instability. Therefore, a combination of
polyphenol and protein removal is necessary. It should be noted that in practice, however, PVPP
and silica gel particles should not be mixed, in order to increase adsorption efficiency.
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Conclusion
In conclusion, colloids in beer are unpleasant. In order to avoid colloidal haze in a brew,
one should be sure to:

Practice good hygiene in brewing

Minimize brew contact with oxygen, and

Remove proteins and/or polyphenols.
The world can only be a better place as a result of these practices. We should all
combine our collective forces and energies into this, as it will decrease the amount of
energy we have to drive while drunk. Kumbaya.
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