Vitality and viability of pitching yeast: methods of assessment and the effect of cellular stress resistance systems.

The article concerns two main topics: 1. Assessment of viability and metabolic competence of yeast by the acidification power test (AP test), its biochemical background, conditions of its use and its development since its introduction, and 2. The way in which the metabolic competence of pitching yeast, and hence the results of the AP test, can be affected by, e.g., the yeast growth phase and the status of the multidrug resistance system (MDR) which underlies the ability of cells to cope with chemical stress caused by xenobiotics. The AP test developed and patented by Opekarová and Sigler, and used by them for the first time to assess the metabolic competence repeatedly pitched in the brewing process, is based on the knowledge of membrane processes taking place in yeast cells metabolizing endogenous and exogenous substrates. The main process contributing to the acidification power of yeast, i.e. the activity of the H+-ATPase, depends not only on cell condition (fresh cells, cells after storage, washing, etc.) but very strongly also on the growth phase. During and closely after the diauxic shift the activity of H+-ATPase in S. cerevisiae sharply drops and remains low during the post-diauxic and stationary phases. This is due to the transition of the cells to an energy saving regime in which energetically demanding processes involving high ATP consumption are downregulated. The MDR transporters exhibit a similar activity pattern.The article concerns two main topics: 1. Assessment of viability and metabolic competence of yeast by the acidification power test (AP test), its biochemical background, conditions of its use and its development since its introduction, and 2. The way in which the metabolic competence of pitching yeast, and hence the results of the AP test, can be affected by, e.g., the yeast growth phase and the status of the multidrug resistance system (MDR) which underlies the ability of cells to cope with chemical stress caused by xenobiotics. The AP test developed and patented by Opekarová and Sigler, and used by them for the first time to assess the metabolic competence repeatedly pitched in the brewing process, is based on the knowledge of membrane processes taking place in yeast cells metabolizing endogenous and exogenous substrates. The main process contributing to the acidification power of yeast, i.e. the activity of the H+-ATPase, depends not only on cell condition (fresh cells, cells after storage, washing, etc.) but very strongly also on the growth phase. During and closely after the diauxic shift the activity of H+-ATPase in S. cerevisiae sharply drops and remains low during the post-diauxic and stationary phases. This is due to the transition of the cells to an energy saving regime in which energetically demanding processes involving high ATP consumption are downregulated. The MDR transporters exhibit a similar activity pattern

Technological aspects of infusion and decoction mashing.

Changes to the mashing processes may be made in breweries in order to save energy and time due to the growing economical pressure. The goal of the experiment was to find and describe any changes in analytical and sensory parameters of beer prepared using different methods and based on the results point out any potential concerns. The same raw materials were used for the brewing, only the mashing processes varied with each individual batch.The experiment was conducted in a pilot-plant scale. Four basic ordinary mashing methods - infusion and single, double and triple mash decoction - were chosen.The mashing was aimed to fully utilize the economic and time advantages of the intensified methods. With the increasing intensity of the method the mash-in temperatures increased and mashing time decreased. The most distinct differences among the individual mashing procedures were shown by the parameters affected directly by the mashing process, like wort colour and coagulable nitrogen, which result from the heat load. Other parameters are dependant on the ;content of the substances entering the kettle boil that is especially bitterness, cold break content, level of solids in Imhoff's cone, content of soluble nitrogen, level of total, oxidizable and oxidized polyphenols, tannoids, anthocyanogens, alpha-glucans and dimethylsulphide in the wort. No significant connections were found between the mashing method and the content of hot break in the wort, the oxalates in the wort and the beta-glucans in the wort and the filtered beer. The content of fatty acids in the wort and the beer as well as the sugars in the wort were comparable, only in the case of two- and three-mash decoction methods higher content of glucose was measured.The content of sugars in green and filtered beer was found to be at the expected level given the degree of attenuation. The clarity of the filtered beer was also comparable given the pilot-plant scale plate and frame filter was used. The mashing process significantly affects the character of the finished beer and that is why it is important to follow the traditional mashing method. Although it is possible to achieve similar analytical results using different technological (mashing) processes, it is obvious that the final effect of the individual beer components will dramatically influence the taste panel results. A change of the brewing process can have fatal consequences especially for Czech beers, which are traditionally brewed using decoction mashing resulting in their exceptional drinkability.Changes to the mashing processes may be made in breweries in order to save energy and time due to the growing economical pressure. The goal of the experiment was to find and describe any changes in analytical and sensory parameters of beer prepared using different methods and based on the results point out any potential concerns. The same raw materials were used for the brewing, only the mashing processes varied with each individual batch.The experiment was conducted in a pilot-plant scale. Four basic ordinary mashing methods - infusion and single, double and triple mash decoction - were chosen.The mashing was aimed to fully utilize the economic and time advantages of the intensified methods. With the increasing intensity of the method the mash-in temperatures increase