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When freezing liquids in glass jars, I know it's important to leave some room for expansion to avoid breaking the jar. To some extent, the more room the safer. But is there a problem leaving too much space in a jar? In other words, I know there's an upper limit for filling the jars when freezing, but is there a lower limit? What if I freeze a half-full jar - will there be any implications for either safety or quality?

I'm thinking freezer burn results in freezer air getting into containers, like onto food in a poorly sealed plastic bag. I'm asking about jars that would be well sealed, with the usual metal lid with mason jars and/or tight tinfoil against the glass.

Sort of a unique use case but I'd think the Q&A applies to any liquids. I'm a new parent and plan to freeze breast milk in jars to avoid plastic containers. I'll try the ice cube method also, freezing 1oz at a time, but when using jars I wonder if it's better to size up to have plenty of space even freezing 4oz at a time. Would the empty space in the jar result in freezer burn or otherwise reduce time the milk is good frozen?

cr0
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From a safety standpoint, there's no lower limit. If you freeze a single drop of water in a one-quart mason jar, you'll get small patch of ice at the bottom of the jar.

From a quality standpoint, a frozen liquid will tend to sublimate and re-freeze; if the amount of liquid is quite small relative to the container, it will tend to re-distribute itself evenly over the inner surface of the container. If the liquid is a mixture of volatile and non-volatile elements (for example, chicken broth), you'll wind up with concentrated liquid at the bottom, and pure water ice everywhere else.

(Source: my experience with freezing pre-measured chicken broth in various containers.)

Mark
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The issue isn't just about headspace for pressure... it's about making sure the liquid doesn't go up to the shoulders of the jar.

Because water expands as it freezes, the shoulder constrains how much the glass can expand, and is much more likely to break when frozen. As such, many folks suggest leaving as much as one inch to the shoulder, which could mean almost 2" (5cm) of headspace.

Most websites that I've seen that talk about freezing in glass jars recommend using 'wide mouth' jars that have no shoulders. This one even has a picture showing a Ball jar that has a 'for freezing' line on it: https://thehomesteadingrd.com/can-you-freeze-mason-jars/

Joe
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