Here’s a quick tip for knowing how much to fill mason jars with food for freezing.
Most straight-sided mason-type jars are made with something called the Freeze-Fill Line. This line shows you how much food you can safety put into a glass jar without risking a cracked jar when the contents freeze and expand. Look for it just under the threads, about an inch down from the top of the jar. Some Mason jars even have “For Freezing” written at this line.
And remember, only freeze food in straight-sided jars, not jars with shoulders. I wanted to show the freeze-fill line on an assortment of jars, but the wide-mouth quart jar shown here is a bit iffy for freezing because it does have slight shoulders.
Why no shoulders?
The liquid expands as it freezes and moves up the jar. Jars with shoulders tend to inhibit this expansion and crack.
Abby – if your jar has shoulders, as the liquid expands it puts pressure on the glass and it will cause the jar to break.
Thank you, ladies! I wondered why some chicken stock that I froze the other week cracked the jar. I was sad, but now I won’t make the same mistake again.
So I just picked up a quart jar and right there, right in the front it says “for freezing —- fill here”. Oh my lord. Big DUH on my part. How come I never noticed that before?
Just when you think you know everything about mason jars, you discover they are even cooler!
Same here! I’ve been canning for long enough to know better. 🙂 Thanks, Erica for the helpful tip!
Sarah M says
I also find I have less trouble with breakage if I chill the jars completely overnight in the fridge before moving them to the freezer. 🙂
Thanks for the post Erica. If folks are going to freeze in glass, this is a good fact to know. I had a jar break once in my chest freezer and I’ve never used glass again. There’s always a nagging feeling that there might be one more little shard that will cut my finger as I’m going to the bottom.
Has anyone experimented with turning the ones with shoulders on their sides to freeze?
There’s more surface area and less depth–it seems like it should help, but I haven’t done it often enough to know if it actually helps.
Amy (Savory Moments) says
This is a great tip – thanks! I have often wondered about freezing glass and the safety of it.
I do freeze in jars with shoulders (they’re the only ones I have), but I only fill up to about one inch *below* the shoulders. Quart jars only hold maybe 3 cups or so, but I’ve never had them break yet.
I Wilkerson says
Well I’m excited. I developed a fixation for onion jam, using it on a pear and goat cheese pizza (http://artofnaturalliving.com/2013/05/17/caramelized-onion-pear-and-goat-cheese-pizza/) and goat cheese and arugula salad (http://artofnaturalliving.com/2013/07/13/caramelized-onion-goat-cheese-and-arugula-salad/) then realized I couldn’t home can it. As my (shoulder-less) jam jars empty out, guess what’s going in them and off to the freezer!
I never knew about the freeze line either, but I always fill to 1-2 inches below that. I put the jars into the freezer without the lid for a day or two, until it is frozen solid. Often liquid items will expand up the neck. Then I screw the lids on tight.
Sarah T says
I freeze soups and broths in jars all the time. I do have breakage from time to time but not enough for me to stop! The Classico 750ml jars seem more prone to breakage.
I use the 500ml jars from Nuts for You almond butter to freeze soups/stews… then just grab a jar to take to work for lunch.
I didn’t know about the shoulders! This explains why my jars cracked when I froze chicken soup in them, even though I thought I left plenty of headroom. Thanks for the explanation.
A friend suggested we start freezing in mason jars about a year ago in order to get away from the ziplock empire. I now use them for almost everything and love it. Thanks for spreading the word.
Ever since a long power outage one winter when all the Ziploc bags of berries, etc., melted and leaked all over the freezer and refroze, I have always used only Mason jars for the freezer too.
I only freeze in glass from store bought honey, pickles etc. and have never had anythink break. I use it for leftovers and stock all the time. I am wondering if letting the contents cool to room temp (like I do) before freezing makes a difference? Any thoughts? Why do jars break?
And P.S. All my jars have shoulders. And sometimes I leave lots of headroom, and sometimes almost none at all. Yet nothing ever breaks.
what does a shouldered jar look like? how can you tell the differance between regular mason jar and shouldered?
Shouldered jars curve in at the top. The Quart sized jar in picture above has a slight shoulder. All off the other one pictures have no shoulder.
So I make big batches of green juice and freeze it, uncapped, in mason jars. I cap them after the juice is frozen so they don’t break. When I take the jars out and thaw them, they often crack. Then I pick through the glass shards and drinking the juice becomes a life-threatening experience. What am I doing wrong?
Erin B says
I would guess thermal shock. Are you thawing in the fridge? It may help
Shannon Simmons says
I freeze stocks in both wide mouth pint and quart canning jars. I’m aware that your not suppose to freeze in the shouldered quarts do to stressing the glass and potentially breaking. I have never had a jar break. I do take the precaution of under filling the quarts, I only fill to the level where the jar starts to shoulder in. Also jars are cooled to room temperature prior to going in freezer and are allowed to gently thaw when they come out of the freezer. Has always worked for me. I do have some of the straight 1.5 pint wide mouth jars that are my favorite. Would love to get my hands on about 6 cases of them.
The 1.5 pint jars are the BEST! Every single one of mine is in use. Time to go shopping…
Great post. I have also been a ziploc guy for a while but I love the mason jar ideas. Cheaper over the long run.
Since I found the 2.5 cup Ball jars for freezers with ‘for freezing–fill here’ on them and NO shoulder, I haven’t had a jar break. They are great!
I have an idea, if you fear broken glass, put in the jar then cover the jar with a plastic bag and zip it in, so if broken glass happens its already in the bag.
Excellent idea. Thank you!!! 🙂
Robby Nunez says
Mmm yeah, let’s use more disposable plastic. Kind of defeats part of the purpose of using a mason jar.
I have what I fear must be a stupid question. If I put warm soup in a jar for freezing and put it in the refrigerator and then froze it, could it have botulism? What does it take to create an anaerobic environment?
Erica / Northwest Edible Life says
No. Botulism does not grow at freezer temperatures. If the soup is cooled to refrigerator temps quickly (within 2 to 3 hours, say), and then frozen it is perfectly safe. Now, if you put warm soup in a jar, sealed it, and left it on your counter at room temp for 3 days – then there is a very good chance botulism could be growing in your jar. Hope this helps.
Thanks! That was very clear. I already ate some of the soup, and it was delicious, but as there is more in the freezer, I am glad to have your reply.
I love food says
My mom said I should look this up and I did. It awosome.
I freeze in all kinds of jars but always leave room for expansion. I use the plastic lids for mason jars they flex more then the metal lids so add a bit more head space (I seal the jar with saran wrap to prevent freezer burn then put on the plastic lids). Also since I do not like clean up of broken glass,all glass in the freezer is placed in reused plastic bags in case of breakage. (reused bread bags, sandwich bags etc) I don’t seal the bags so reusing bags with holes at the top or broken zippers is OK. If there is breakage it’s reasonably contained. I’ve actually only broken jars when I’ve dropped them in the freezer, they’ll stick to anything wet, (I double dog dare ya) but they were still in their bag so clean up was minimal.
PinkEye Pete says
If I am to use the mason jars for smoothies, what time would I take the mason jars out so that they are defrosted and ready to eat for breakfast? Would a month be long enough?
My daughter broke a mason jar in the freezer today. She was thawing the half of the jar that was still stuck to the food so that she could pull the glasses off of it and consume the failed smoothie. I’m trying to educate her on freezing glass and expansion. She’s a 21 years old college student and having a hard time taking my advice. My advise is throw out the problem and start over. I’m afraid that she with consume glass shards. Can you email her some info?
I hate wasting food, but when I found a cracked soup broth jar in the freezer I decided to thaw it upside down in a mesh colander, and sure enough, even tho I thought I had gotten off all of the glass pieces, when it was all melted there were small shards of glass in the strainer. I just found another cracked jar today (that’s why I’m here tonight to learn what I was doing wrong) and had no thoughts of saving the contents. I hope your daughter will learn from me, and keep on learning. I’m 56!
Suzanne Rice says
Can I use canning jars from the grocery store for freezing even if they don’t say freezer jars on the package? I bought a dozen online a couple months ago that said they were for freezing, but because they weren’t packed with much padding, one of them was broken. Otherwise, they are just fine. But I wanted to see if I could just get the ones my grocery store sells (Ball brand) and use those so they aren’t being shipped and potentially break in the mail. I don’t remember them saying they are for freezing though. Does that matter? Thanks!!
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