Fermentation temperature is the thermal condition imposed on a culture during a biological conversion process, expressed as a set point, range, or programmed time profile. It influences enzyme reaction rates, membrane properties, growth kinetics, product formation, gas solubility, and the balance between competing metabolic pathways [1]. A temperature shift can therefore change both biomass accumulation and the composition of metabolites or recombinant products. The measured value usually represents bulk broth temperature, whereas cells may experience local differences when heat generation, viscosity, or mixing limitations create gradients [2]. Temperature control combines metabolic heat generation with heat transfer through the vessel wall, cooling surfaces, evaporation, and incoming or outgoing streams [3][4]. The useful operating range is organism- and product-specific: temperatures that maximize growth may not maximize folding, secretion, aroma formation, or product stability. The profile is selected together with inoculum state, oxygen supply, pH, feeding, and harvest timing [5].