 We talked about using heat before, so we're going to start here by talking about cold. Just so you know, this is kind of a miscellaneous video, I'm going to cover cold pressure and desiccation or drying all in this video. So they're all important, but I didn't want to make separate videos for each one. So cold, let's talk about refrigeration versus freezing. So refrigeration will work, it inhibits metabolism, doesn't kill organism. So the key word there is that low temperature like refrigeration has a bacteriostatic effect. It will keep microbes from growing or slow them from growing, but it will not actually kill them. So it's bacteriostatic, not bactericidal. Now freezing, if you get below minus 2 degrees Celsius or centigrade, can actually kill some microbes, but not all. There are psychrophilic organisms actually love this temperature, so we'll cover that in a different video. But refrigeration is great at slowing microbes down by inhibiting their metabolism. If you want to stop the metabolism of almost all organisms and kill some, then you'd use freezing. So you can even have ultra low temperature freezing though. So you can, there are freezers full of dry ice that can maintain things at negative 70 degrees, or here I have a picture of using liquid nitrogen. These tanks are going to maintain a temperature of minus 196 degrees Celsius there. So that's how we use cold to control microbes. Next we have pressures. You may not have heard about this much, but it is being used in food. I've seen it primarily used like in some, like in deli meats and pre-cooked meats, but juices are where I've seen it used the most. So high pressure can denate your proteins and cause some cells to rupture, just like using heatwood. But the advantage of using high pressure is that it appears to maintain the quality and shelf life of the food better than using heat, at least in those situations, the examples I gave you. So it can kill, if you want to say it can kill viruses, parasites, mold, fungi, all sorts of things. So what's crazy about this is the amount of pressure it takes. So it says there are 100 to 800, that would be a megapascals. So the other term for using pressure to control microbial growth is pascalization instead of pasteurization. I'll put that on the screen, but 100 to 800 megapascals is a huge number, right? The atmospheric pressure at sea level is 0.1 megapascal in that ballpark. So I did the math, 800 megapascals would be over 116,000 pounds per square inch. Think about like your car tire with 30 pounds per square inch, or even our autoclave only uses 15 pounds per square inch. So we're talking about massive amounts of pressure. The same issues with lots of other microbial control techniques, it can kill the living vegetative cells good or well, but it has a hard time with the endospores just like most of the other ones. So that's how you might use pressure or pascalization. Next, we have desiccation or drying. So the key here is that microbes in all living things can't have a metabolism without water, right? So drying just sucks the moisture, sucks the water out of things, and that slows the metabolism. So the examples you have here would be like drying fruits, like making raisins or jerky, those kind of things. So pretty simple. That'd be like sun drying. It's far from making things sterile. You're definitely not going to kill all the food spoilage organisms or the pathogens, but it's better than nothing for sure. The next thing you can do is just actually remove the moisture. I mean, you keep the liquid around, but you remove the moisture or liquid from individual cells by adding salt or sugar is what that should say there. So you reduce the water activity. So you see a picture here. This is a red blood cell, but if you put a cell in a hypertonic environment, it sucks all the moisture out of the cell and that slows or stops its metabolism. So this would be like the reason, you know, honey is almost all sucrose. The reason that that's why living cells don't live in it, right? There are still spores though, which is why children under one shouldn't consume honey. So you add sugar to things like vegetables and making jams and jellies. You add salt to like your canned goods. So you're creating a hypertonic environment, sucking the moisture out of these cells. Now the term, which I do want you to know is called plasma lysis. So if you remove the moisture, remove the water from a living cell, it's called plasma lysis. So that's going to be creating a hypertonic environment. Think about your canned goods from the grocery store, mainly. And then the last example here would be lyophilization. So this is something that we don't ever do in the lab, but we do get a lot of our supplies have been lyophilized. Like the DNA we use in our DNA based labs has been lyophilized. And so have all the bacteria we work with. We buy lyophilized samples that we keep in our refrigerator. And then we rehydrate them and warm them up and we want to use them. So lyophilization, think like a rapid freeze drying under a vacuum. So you're going to freeze dry these super quickly. They call it snap freezing or snap frozen. But then under a vacuum, which is going to remove all the moisture. So you've basically frozen this while you've dried it. And that's what lyophilization is. Okay. So those are three more methods of microbial control using pressure. I don't remember the other one I did. So cold pressure and removing water. All right. I hope this helps. Have a wonderful day. Be blessed.