Nutrient media, metabolic effects

Most of the reports on the effects of HA on the nutrient contents of plants are purely descriptive and little attempt was made in the earlier work to elucidate the mechanisms of the action of the humic material. The final concentration of a nutrient in a plant can depend on a number of factors such as the concentration in the nutrient solution, its interactions with other nutrients and/or humic substances, the pH of the nutrient medium in addition to the effects of the humic substances on the ion uptake mechanism and finally translocation within the plant. Several of these factors are well illustrated in a recent paper by Guminski e al. These workers showed for example that Mg is taken up to a greater extent at pH 5.0 than at pH 7.0 and that, in general, humate stimulated Mg uptake at both pH values. Guminski e a also demonstrated that the metabolic inhibitor 2,4-dinitrophenol had an adverse effect on any stimulation of ion uptake produced by HA. Such a result demonstrates that humates can influence nutrient concentration in plants directly through metabolic processes. 

All of these factors, individually or more often in combination with one another, permit the definition of the requirements of an acceptable brewer s yeast strain (Stewart Russell, 2009). To achieve beer of high quality, not only the yeast must be effective in receiving the required nutrients from the growth/fermentation medium (the wort), able to tolerate the prevailing environmental conditions (e.g. osmotic, temperature and ethanol tolerance) and impart the desired flavour to the beer, but the microorganisms themselves must be effectively removed from the fermented wort by flocculation, centrifugation and/or filtration after they have fulfilled their metabolic role. 

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