In order to prevent fermentation problems, the number of dead yeast cells in the brewery yeast should be as low as possible. Pitching yeast should have a dead yeast content of less than 2 %, exclusion limit from 5 %. Fresh propagated yeast should usually have a dead cell count of 0 %.
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.