Physical Methods for Controlling Microbial Growth: Temperature

Heat controls microbial growth by killing microbes through the inactivation of essential proteins.

During heat treatment, the thermal death time — or TDT — is the time required to fully sterilize a suspension at a specific temperature.

While the thermal death point — TDP is the lowest temperature at which all microbes are killed in 10 minutes.

The D value, or decimal reduction time, is the time needed at a specific temperature to reduce a bacterial population by 90%, corresponding to one-log reduction.

Moist heat kills microbes more efficiently than dry methods, but pressure is needed to destroy spores.

Pressurized moist heat in autoclaves raises steam temperatures to 121°C, sterilizing heat-resistant endospores that typically survive boiling temperatures of 100°C.

Pasteurization heats sensitive liquids like milk, reducing microbial load and extending shelf life.

Modern methods include high-temperature short-time, or HTST, pasteurization, which heats milk to 72°C for 15 seconds, and ultrahigh-temperature, or UHT, processing at 135°C for longer shelf life.