Why is pH control important in fermentation?

pH affects enzyme activity, cell membrane function, nutrient uptake, and product stability. Each organism has an optimal pH range (bacteria typically 6.5-7.5, yeast 4.5-6.0, mammalian cells 6.8-7.4). pH changes during fermentation due to metabolite production (organic acids, ammonia) and nutrient consumption. Control is achieved by adding acid (H2SO4, HCl, phosphoric acid) or base (NaOH, KOH, NH4OH - which also supplies nitrogen). pH probes must be calibrated and maintained. Improper pH leads to reduced growth, altered metabolism, enzyme inactivation, and product degradation. Buffer systems provide additional stability.