In this video, we're going to begin our lesson on moist heat as a physical method for controlling microbial growth. Most microbes require very specific temperatures for normal growth and reproduction to occur. Exceeding those temperatures by applying heat, either dry heat or moist heat, can destroy microbes. Moist heat is specifically a form of heat that has moisture, as its name implies, or you could define it also as heat that has liquid content in it.
Moist heat is capable of killing microorganisms by irreversibly denaturing their enzymes and proteins. Moist heat is typically going to be more effective than dry heat because it generally requires lower temperatures and less time to kill microbes than dry heat does. Dry heat usually takes longer to kill microbes, and it requires higher temperatures generally.
Examples of moist heat include boiling, pasteurization, which is really just a brief heat treatment, and it also includes pressurized steam. Later in our course, we're going to talk more about pasteurization, this brief heat treatment. What you should know about pressurized steam is that an instrument known as an autoclave, which somewhat resembles a pressure cooker, uses high temperatures and pressurized steam to sterilize heat and moisture-tolerant items.
An example of moist heat is boiling, where liquid is heated to a high temperature. Another example is pasteurization, a brief heat treatment. Here, we're showing you an image of milk being pasteurized. We'll talk more about pasteurization in our next lesson video. Pressurized steam is used in a device known as an autoclave to bring in heat and steam; the steam creates high pressures and heat, moist heat, in order to sterilize items that are heat and moisture-tolerant. The waste, air, and steam are able to exit through the back.
On the right, we are showing you a table that demonstrates that dry heat typically requires a lot more time to sterilize compared to moist heat. Using the same temperature of 121 degrees Celsius, moist heat is able to kill more effectively; it takes much less time, only 15 minutes here to kill or to sterilize the item, in comparison to 600 minutes or 10 hours when using dry heat. This shows that moist heat is more effective than dry heat. However, there are advantages and disadvantages to each of these methods. Even though moist heat can be more effective, moisture might not always be compatible with the item to be treated. Sometimes dry heat is a better method simply because of the compatibility of the items.
This here concludes our brief lesson on moist heat. We'll be able to apply these concepts and learn more about pasteurization and other physical methods to control microbial growth as we move forward in our course. I'll see you all in our next video.