Ascospore

Ascospore Saccharomyces
Figure 1. Yeast life cycle. Most lab strains form ascospores containing spores of opposite mating types, a and a. These spores can mate, hybridize, and form diploidal cells capable of budding or sporulating. In contrast, brewing yeasts generally only reproduce by budding.

chain reaction (PCR), restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP), pulsed field gel electophoresis (PFGE), and karyotyping all provide unique genetic fingerprints that distinguish not only between ale and lager yeasts, but also between strains of the same group.

Table 2. Characteristics of Saccharomyces species used in brewing1.

Fermentation of:

Assimilation of:

Species

Fructose transport

Assimilation of:

Growth at:

Suc2 Raf Tre Suc Mal Raf Man Eth activity Lys Cad Ety 30°C 37°C

S. bayanus3 S. cerevisiae S. exiguus S. paradoxus4 S. pastorianus5

Adapted from Vaughan-Martini and Martini, 1998

Abbreviations: Suc, sucrose; Raf, raffinose;Tre, trehalose;Mal,maltose;Man,mannose; Eth, ethanol; Lys,lysine; Cad, cadaverine; Ety, ethyl-amine; s, positive, but slow; v, variable; u, undetermined

3synonyms: S. uvarum

4synonyms: S. cerevisiae

5synonyms: S. carlsbergensis v v s v

Box 9—5. Classification of Brewing Yeasts (Continued) References

Dufour, J.-P, K. Verstrepen, and G. Derdelinckx. 2003. Brewing yeast, p. 347—388. In T. Boekhout and V Robert (ed.), Yeasts in food.Woodhead Publishing Limited, Cambridge, England and CRC Press, Boca Raton, Florida.

Hammond,J.R.M., 2003.Yeast genetics,p.67—112. In F.G.Priest and I.Campbell (ed.), Brewing Microbiology, 3rd ed. Kluwer Academic/Plenum Publishers. New York.

Kurtzman, C.P., and J.W. Fell. 1998. Definition, classification and nomenclature of the yeasts. P. 3—5.In C.P. Kutrzman and J.W. Fell (ed.), The Yeast: A Taxonomic Study, 4th Edition. Elsevier Science B.V. The Netherlands.

Vaughan-Martini,A., and A. Martini. 1998. Saccharomyces Meyen ex Reess, 358-371. In C.I? Kurtzman and J.W. Fell (ed.), The Yeast:A taxonomic study, 4th Edition. Elsevier Science B.V.The Netherlands.

Table 9.4. Differences between ale and lager yeasts.

Ale (Saccharomyces cerevisiae)

Lager (Saccharomyces pastorianus)

Flocculated yeast rises to the top Optimum growth temperature > 30°C Minimum growth temperature = 15°C Maximum growth temperature = 40°C Cannot metabolize melibiose Slow assimilation of maltotriose Sporulating (at low frequency)

Flocculated yeast settles to the bottom Optimum growth temperature < 30°C Minimum growth temperature = 7°C Maximum growth temperature = 34°C Able to metabolize melibiose Efficient assimilation of maltotriose Non-sporulating

previous fermentation to pitch the next batch. Only when the fermentation appears slow or sluggish or when quality attributes suffer will a new culture be prepared.

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Responses

  • MICHELLE
    What is budding sporulation?
    6 years ago

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