Patent No. EP0070570B1: Yeast Strain For Use In Brewing

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Today in 1989, US Patent EP 0070570 B1 was issued, an invention of George Stewart Graham, Edmund Goring Thomas and Russell Ingeborg, assigned to the Labatt Brewing Company, for their “Yeast Strain For Use in Brewing.” There’s no Abstract, although in the description it includes these claims:

This invention relates to a novel yeast strain suitable for use in the brewing of beer and to a method of preparing the same.

In the brewing of beer, i.e. ale and lager, ale yeast strains (Saccharomyces cerevisiae) are traditionally top-cropping strains and lager yeast strains (Saccharomyces uvarum (carlsbergensis)) are bottom-cropping strains. That is, when the attenuation of the wort, which may be broadly defined as the conversion of fermentable substrate to alcohol, has attained a certain level, the discrete yeast cells of most ale strains adhere or aggregate to an extent that, adsorbed to bubbles of carbon dioxide, they will rise to the surface under quiescent conditions (e.g. when the medium is not agitated) where they are “cropped” by being skimmed off. In the case of lager strains, the aggregated cells are not adsorbed to bubbles of carbon dioxide and settle out of suspension to the bottom of the vessel where they are “cropped” by various standard methods.

One of the limitations of the known ale yeast strains is that they do not function satisfactorily in worts having plato values (°P) higher than about 14.5°P and values of only about 9°P to 12°P are usually required. The plato value (°P) is defined as the weight of dissolved solids, expressed as a percentage, in water at 15.6°C. Generally, the higher the plato value at which a yeast strain will function, the greater is the conversion of fermentable substrate to alcohol for a given volume of wort. Consequently, the resultant fermentation product would be one of higher than usually desired final alcohol content and would generally be diluted before packaging. Since the dilution to obtain a standard, commercially acceptable product would occur at the end of the brewing process, the overall throughput of such a brewing system would be substantially increased over a conventional system. Furthermore, beers produced from such high plato worts generally exhibit improved colloidal haze and flavour stability.

In view of the economic advantages possible in fermenting worts of higher plato values, there has been a substantial amount of research carried out in the hope of obtaining a yeast strain which will function at such higher plato values in the range of about 16°P to 18°P, i.e. a yeast strain which will remain in the body of the wort until substantial or total conversion of the fermentable sugars to alcohol atthe higher Plato values has occurred. As an alternative, attempts have been made to maintain known yeast strains in the body of the wort by mechanical means, such as continuous stirring, in the hope thatthe yeast would continue to function if maintained in contact with the wort. However, this has proved to be inefficient and in many cases more expensive because of the extra energy required to operate such mechanical means. Furthermore, many such attempts have been frustrated by difficulties of product flavour match with present commercially acceptable standards.

The inventors of this invention have now discovered a yeast strain which is an ale yeast (species Saccharomyces cerevisiae) that not only functions at high plato values, e.g. up to about 18°P, but also flocculates to the bottom of the fermenting vessel when conversion or attenuation has been substantially completed (the latter feature, as noted above, is usually characteristic of a lager strain rather than an ale strain).

The present novel organism was found to be a component of a mixture of ale yeasts maintained by the assignee. The organism was isolated and biologically pure cultures thereof were produced by techniques considered standard by those skilled in the art and can be obtained upon request from the permanent collection of the National Collection of Yeast Cultures (termed “NCYC” herein), Food Research Institute, Norwich, Norfolk, England. The accession number of the organism in this repository is NCYC No. 962.

Thus, according to one aspect of the present invention there is provided a brewing process wherein a malt wort is prepared; fermented with brewers’ yeast; and, following completion of the fermentation, finished to the desired alcoholic brewery beverage; the improvement comprising fermenting said wort having a Plato value of about 14.5 or greater with a strain of the species Saccharomyces cerevisiae brewers’ yeast having the NCYC No. 962.

In another aspect the invention provides a brewing process for producing ale, wherein a hopped, 30% corn grit adjunct wort is prepared having a Plato value of from about 16°P to 18°P; fermented at a temperature of about 21°C for about 3 to 5 days with a species of Saccharomyces cerevisiae brewers’ yeast; and, following completion of the fermentation, finished to the desired ale; the improvement comprising fermenting said wort with a strain of the species Saccharomyces cerevisiae brewers’ yeast having the NCYC No. 962.

In a further aspect the invention provides a biologically pure culture of a brewers’ yeast strain of the species Saccharomyces cerevisiae having the NCYC No. 962, said strain having the ability to ferment high Plato value worts of 14.5 or greater and the ability of flocculate to the bottom of the fermentation vessel when attenuation is substantially complete.

In a further aspect of the invention provides a method of manufacturing a novel brewers’ yeast strain, wherein a yeast strain is propagated in an oxygenated nutrient medium, the improvement comprising propagating a biologically pure culture of a yeast strain of the species Saccharomyces cerevisiae having the NCYC No. 962.

The advantage of the yeast strain of the present invention (referred to herein as strain 962 for the sake of convenience) is that it has both bottom-cropping characteristics as well as the ability to ferment high specific gravity worts. The bottom-cropping characteristic is advantageous because of increased utilization in the brewing industry of large conical-based vessels for fermenting the wort, and bottom-cropping is especially facile in such vessels. Thus strain 962 is particularly well adapted for use with continuous brewing techniques as well as batch-wise brewing.

The fact that strain 962 can ferment worts having high plato values is economically advantageous in that use of such worts allows dilution with water at a much later stage in the processing, generally prior to packaging. By reducing the amount of water required in the majority of process stages, increasing production demands can be met without the expansion of existing brewing, fermenting and storage facilities and the overall throughput of an existing brewery system can be substantially increased by the use of strain 962. Consequently, the brewing process can be carried out at a reduced overall cost, including a reduced energy cost.

Thus, while a number of bottom-cropping ale strains are known, the dual characteristics of bottom-cropping and the ability to ferment which gravity worts makes strain 962 of the present invention especially useful in the brewing of ale.

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