Industrial yeasts from the brewing process.
Live, aerobic yeast cells possess dehydrogeneases which reduce the methylene blue absorbed into the cell to its colourless leuco form, giving the cells a pale blue colour. Dead or inactive cells lack dehydrogenase activity and turn an intense blue colour.
Determination of the vitality of brewing yeasts
The acidification power is defined as the acidification of a solution of distilled water with a defined pH of 6.3 and a glucose concentration of 5 % at 25 °C by a yeast.
The pH curve is documented and serves as an indication of yeast vitality.