Now, let’s get specific about the magic number: 250 degrees. This is actually a pretty safe temperature for most modern, name-brand mason jars (looking at you, Ball and Kerr). Why? Because it’s below the “thermal shock” danger zone—usually 300°F to 350°F—where the glass starts to protest loudly.
I’ve baked mini cheesecakes at 250°F in a Ball jar and it felt like a victory lap. I did a little dance. My cat gave me a judgmental look. Worth it.
But remember: It’s not just the temperature; it’s the change in temperature. Don’t take a cold jar straight from the fridge and toss it into a preheated 250°F oven, unless you want a glass confetti party in your kitchen. Let it warm up on the counter for 20 minutes like a sleepy bear.
