Moist Heat Vs Dry Heat

Moist and dry heat Bacterial growth in food and laboratory equipment is controlled through sterilization. Different techniques and tools, such as moist heat and dry heat are used in the process of sterilization. Moist heat involves autoclaving or pressure cooking, tyndallisation and boiling and microorganisms are killed by denaturing their proteins as water molecules disrupt the hydrogen bonds.

Conversely, dry heat involves conduction and is mostly used for laboratory instruments. The heat changes microbial proteins by oxidation reactions creating an arid internal environment, oxidative free radical damage, and drying of cells. Some microorganisms are more resistant to heat than others because of their adaptability to hotter conditions, for instance Clostridium tetanus.

Moist heat is more effective than dry heat because the moist heat penetrates microorganisms and spores thus denaturing their proteins. However, dry heat requires higher temperatures than moist heat because water has a higher heat capacity than air as water conducts heat better than air. In heat sterilization, time and temperature relate to the killing rate with thermal death point being the temperature that kills all the bacteria in a 24-hour broth culture at neutral pH in 10 minutes. The higher the temperature the lesser the time it takes to kill the bacteria.

The autoclave

In dry heat, sterilization involves distribution of temperature with a fan. The autoclave is effective at 121-124 degrees Celsius, at a pressure of 15 psi for 15 minutes. The time period necessary for steam-pressure sterilization is determined by altitudes, whereby time is increased at high altitudes to compensate for the lower boiling point of water. Further, time to reach sterilizing temperatures depends on material for moist