WHAT'S IN YOUR GLASS?

Introduction

A large number of fish by-products have been developed and some of them are produced on commercial scale. By-product means a subsidiary product produced incidentally while manufacturing some other major product, or a product made from some part or from out of the waste material resulting from the manufacture of a major product. 

Isinglass is one of the fish by-products. It can be extracted from the swim bladder of fishes. It is an excellent raw material for producing fish gelatin and it has been used for few centuries to clarify alcoholic beverages. To produce isinglass, the swim bladder is processed by eviscerating it from the dorsal portion of the fish and cut lengthways. It is then softened in hot water followed by separation of the outer muscle layer and blood. The swim bladder is then stretched for drying.



Figure 1 Isinglass derived from the swim bladder of fish.

Source. http://www.historicfood.com/isinglass.htm

Retrieved on 27 April 2018

Structure and function of swim bladder

The swim bladder is a compressible sac containing air. It is located in the abdominal cavity below the vertebral column, and consists of several external membranous layers or coatings, the innermost layer being the thinnest. The layer adjacent to the innermost layer is high in collagen.

Basically, the function of swim bladder is to regulate the specific gravity of the fish, so that it can maintain its position at any level in the water. Not all fish swimming bladder are suitable to produce isinglass. To produce isinglass, the swim bladder should be relatively large and easily detachable from the fish. For example, fishes such as hake, sturgeon, and crap. 

Figure 2 Structure of swim bladder.

Source. http://www.govegan.org.uk/the-vegan-boozer-by-fiona-pereira/ 

Retrieved on 27 April 2018

Composition of isinglass

Isinglass is a natural product. Thus, only approximate values can be provided:

Moisture level 10-25 %

Ash max. 1 %

Protein content 75-85 %

Properties of isinglass

The active ingredient in isinglass is collagen. Collagen is a rigid, linear, rod-like triple helical protein. It is characterised by an unusual amino acid profile containing high levels of glycine and proline, no cysteine, and is almost unique in containing both hydroxyproline and hydroxylysine. Collagens derived from the swim bladders of different fish species have different amino acid compositions. This in turn impacts on properties of the isinglass such as fining activity, viscosity, thermal stability, and charge characteristics.

As collagen is a protein of high structural order, it thermally labile. It will undergo thermal denaturation to form the random coils of gelatin at high temperature.  Isinglass is no longer effective as a clarifying agent if thermally denatured hence the collagenous triple helical structure must be maintained. This has significant implications for the manufacture and storage of isinglass finings. Isinglass also dissolves readily in most dilute acid and alkali but insoluble in alcohol.

Differences between fish and mammalian gelatin

Isinglass is an excellent raw material for producing fish gelatin. However, gelatin from aqueous source is not as good as gelatin from animal source. The main difference between the fish and mammalian gelatin is the content of amino acids proline and hydroxyproline. The lower content of proline and hydroxyproline gives fish gelatin its low gel modulus, gelling and melting temperature. In addition, the amino acid composition of mammalian gelatin are remarkably constant when compared to those from different species of fish, resulting in large quality variation. Also, the collagenous material from the fish is more susceptible to degradation during chemical treatment, in contrast to the more stable mammalian collagen.

Uses of isinglass

Isinglass is a substance that can be used to clarify beverages like wine, beer and vinegar. In unclarified beer, yeast cell walls carry a negative charge. Isinglass and gelatin solutions are proteins that carry a positive charge. When added to newly fermented beer, the charged finings interact with the yeast and neutralize the zeta potential present on the cell wall. This eliminates the repulsive forces and sticks the yeast cells together to form a larger particle called a floc, which will settle to the bottom. Isinglass help to reduce the suspended solids in beer and increases the filtration rate. The use of isinglass has decreased with modern brewing methods, and not all brands of cask ales use the fishy glue to clarify their product. But there are other animal-derived, vegan- or vegetarian-unfriendly additives that can make their way into brew, including glycerol (derived from animal fat), honey (which is basically bee vomit), and lactose (derived from milk). Fish bladders had been used in the production process for Guinness for years.

            Isinglass can also be used as an adhesive base. When dissolved in acetic acid, it forms a strong cement especially useful for glass or pottery. Modified isinglass can be used for repairing leather belts.

            Isinglass also known as Marine ginseng. It is believed that this collagen rich fish bladder may slow down skin aging process by replenishing the collagen leaving one’s skin looking youthful and full of elastic.

Conclusion

Isinglass is widely used commercially to clarify alcoholic beverages by aggregation of the yeast and other insoluble particles. Isinglass is no longer effective as a clarifying agent if thermally denatured hence the collagenous triple helical structure must be maintained. Fish products have been identified as serious allergens and people who are allergic to fish must avoid consuming foods made with fish or fish products. The most widely researched alternative to isinglass for beer fining is the use of bovine gelatin. Bovine gelatin has been used on an industrial scale for both beer and wine fining. The higher thermal denaturation temperature, ready availability and reproducibility of bovine collagen preparations gives it considerable advantages over isinglass.

References

Hickman, D., Sims, T. J., Miles, C.A., Bailey, A. J., Mari, M. (2000). Isinglass/collagen: denaturation and functionality. Journal of Biotechnology, 79, 245–257.

Martin, R. E., Carter, E. P., Flick, G. J., Davis, J. L. M. (2000). Marine and Freshwater Products Handbook. USA: Technomic Publishing Company.

Walker, S.L., Camarena, M. C. D., Freeman, G. (2007). Alternatives to Isinglass for Beer Clarification. Journal of the Institute of Brewing, 113(4), 347-354.