Colloidal Brew

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 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.

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 90-degree 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.

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 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.

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.

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.

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.

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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