Okay, fair question. Freezing can kill some bacteria, but it’s the equivalent of trying to kill a cockroach by staring at it. The key is rate and temperature. If you freeze water very slowly, the ice crystals grow big and spikey, and they can puncture the cell walls of a few wimpy bacteria. But standard home freezers? They’re too gentle.
Does Bacteria Live In Ice at Jennifer Johansen blog
Another trick: if the water contains a lot of salt or sugar (like broth or juice), the freezing point drops even lower. That just gives bacteria an even cushier, colder vacation. The only way freezing reliably kills bacteria is at ultra-low temperatures—think liquid nitrogen levels (-320°F). At that point, the cells shatter like tiny glass figurines. But you’re not pouring liquid nitrogen into your Nalgene bottle, are you? I didn’t think so.
The Real Danger: The Thaw
Here’s the kicker—the part that’ll make you spit out your iced coffee. When you freeze water that has bacteria, you don’t kill them. You just pause the video. The moment you take that bottle out and it thaws, the bacteria wake up, stretch their microscopic legs, and go, “Wow, what a refreshing nap! Time to party!”
In fact, the thawing process can increase their numbers. As ice melts, the water becomes liquid again, and if the food source (sugar, dirt, your leftover sandwich crumbs) is still there, they multiply faster than before. It’s like putting the entire cast of Walking Dead in a coma, then waking them up in a buffet.
Does Freezing Really Kill Bacteria? - What the Science Says
