A recent article which outlined tips for successfully freezing milk and other dairy, especially when the milk is fresh from the farm or non-homogenized (cream top), triggered questions about what type of material is best for freezer containers.
Several very insightful comments from that article related to this concern got me rethinking my choice of plastic for freezer containers, and it seemed an article on the subject was warranted to explore the issue more thoroughly.
All things considered, which truly is the best material to use for freezer containers – plastic or glass? And, while glass may be the obvious green choice, it is really practical to use safely especially with children in the house, and if so, how?
Plastic Freezer Containers
The good news is that if you’ve been using plastic as your freezer containers of choice, the practice is probably not leeching a ton of chemicals into your food contrary to what some would lead you to believe. Cold plastic does not leech chemicals at a rapid rate like heated plastic does. So, while you should never put hot food or liquids into plastic containers, storing cold or frozen food in plastic is usually safe as long as you aren’t scratching the plastic with metal utensils, using cheap, single use plastic or old containers that are visibly breaking down. In addition, acidic liquids (like apple cider vinegar) and foods (tomato sauce) should never be stored or frozen in plastic as the acidity alone tends to leech chemicals out of the plastic.
Here are some other tips from Environmental Working Group (EWG) for safe use of plastic in the kitchen for food storage and as freezer containers (1):
- Don’t microwave food or drinks in plastic containers — even if they claim to be “microwave safe.” Heat can break down plastics and release chemical additives into your food and drink. In addition, microwaves heat unevenly, creating hot spots where the plastic is more likely to get too hot, break down, and release chemicals.
- Use plastic containers for cool or frozen liquids and food only — never hot.
- Don’t reuse single-use plastics. They can break down and release hormone disrupting chemicals when used repeatedly.
- Avoid old, scratched plastic containers. Exposures to the chemicals in plastic may be greater when the surface is worn down.
- Wash plastic containers by hand with mild dishsoap and only using warm (never hot) water.
If you follow these guidelines for using plastic for freezing, it is a relief to know you are most likely not exposing yourself and your family to chemicals. However, plastic is clearly not as green a choice environmentally speaking as glass for freezer containers.
If you would prefer to up your game with regard to freezer containers and transition to glass, which is clearly the more planet-friendly choice, you will be happy to learn (as I was) that it is possible to use glass safely!
Several folks have shared with me recently how to use glass freezer containers safely and make cracks and breakage a thing of the past.
Using Glass Freezer Containers
The key to safe usage of glass for freezer containers is choosing the right glass jars. If you’ve had a lot of breakage when attempting to freeze food in glass, take heart. You’ve probably just been using the wrong type of jars.
Two things in particular impact the chance of breakage when using a particular glass jar as a freezer container:
- Age
- Shape
Old glass jars will break much more readily than new ones. Make sure that the glass containers you select for freezing are new or relatively so and put a plan in place to replace them every so often if you use them as freezer containers on a regular basis.
Glass Jar Shape is Crucial to Freezing Success
While the age of the container is important, the shape of the glass container is critical. Be sure that the glass jars you choose as freezer containers are straight sided if at all possible. This is because if there is any narrowing of the container toward the top, the container will probably crack during the freezing process. If you remember from high school chemistry, as liquids containing water freeze, they expand upwards, hence the tendency to crack glass containers if that expansion process is restricted in any way by the container’s shape.
If there is no narrowing of the container during this upward expansion, problems and cracking/breakage are unlikely. Don’t worry if the jars you want to use curve at the bottom. The narrowing and curving toward the top of the jar is what matters most.
It is common sense, of course, not to fill a glass container that will be put in the freezer filled to the top with liquid. Even if a straight sided jar is used in that case, it will still crack when the expanding liquid encounters a screwed on lid. If you wish to be extra safe to ensure no cracking of a glass jar, leave off the lid entirely until the liquid has completely frozen inside the jar, then gently screw on the lid but never too tightly. Waiting until the food/liquid inside the jar is frozen before putting on the lid will also extend the life of the jar for freezing purposes.
If you have curved jars that narrow toward the top, no need to replace them if you wanted to use them as freezer containers. Simply leave enough room for expansion so that the frozen liquid won’t ever reach the narrowed portion of the jar.
Safest Way to Use Glass as a Freezer Container
If freezing in glass still has you nervous even after reviewing the guidelines above, it would be best to stick with commercial canning jars that are labeled as freezer safe.
Freezer safe jars (like these) are not only straight sided, but also have a handy fill line marked right on the jar so you know exactly how much food or liquid to put in to prevent any breakage issues.
Buying canning jars labeled as freezer safe with a maximum fill line etched right on the glass takes all the guesswork out of the process. These containers permit the use of glass – the greenest and healthiest material for freezer containers – to be used without worry.
BPA Free Lids for Your Glass Jars
I have one more tip to pass along when choosing and using glass for freezer containers. Be sure to use jars that come with BPA free lids.
Metal, screw-on lids that have white plastic on the underside of the lid are not preferable to metal lids that are plain metal on the underside. Alternatively, you can choose BPA free plastic lids (like these) for your glass jars, but in my opinion, the plain metal screw on lids are better because they don’t use any plastic at all.
Do you have any other tips for safe, green freezer containers? Please share with all of us in the comments section.
Sarah, The Healthy Home Economist
I hope everyone realizes that a hot jar on a cold freezer surface would almost surely explode.
Also, metal lids have a rubber or plastic gasket on the bottom of the flat part. If the lid is solid metal, a firm seal wouldn’t take place.
Sarah, you mentioned “metal lids that are plain metal on the underside”. Can you please provide more information on where to find these types of lids? I have been searching a long time and have never found any. The best I can do is the BPA free but would rather just have metal only. Thank you!
The all-metal lids I have for my mason jars came with them … bought them at Big Lots.
What do you freeze your bread in?
I freeze in straight sided 24 ounce Ball jars. It works great!
I have a silicone baking tray with cavities shaped for for baking bars. I pour my bone broth into the cavities, freeze, pop out and put in large ziplock bags. I find this makes my broth much easier to use. If I want just a little, I don’t have to thaw out entire jar. I can just grab a couple bars if I want.
I have learned so much from this article, and the comments. You have probably prevented an injury to my family. I was using clean pickle jars to store my broth in the freezer.
Wow, I didn’t even think about putting plastic rubbermaid containers in the dishwasher, but I suppose that isn’t the best idea. Instead, I should be washing them by hand. Great info, as always!
Glad it helped Susie 🙂 Sometimes we get in a rut with our household routine. I know I’m guilty of this and it’s good to have outside input to get us thinking about it and improving as there are lots of ways we can tweak things for the better all the time.
I have moved toward buying the Pyrex and generic glass containers for food storage. They are attractive for serving food and are freezer safe. They are glass with a plastic/rubber lid that seals down on them. They are very expensive, but they stand the test of time. The name brand Pyrex lids hold up better than the generic ones (anchor hauling). I’d love to have the old timey sets, with the decorative designs, but they are very hard to find. The modern ones are usually clear. Pyrex’s claim to fame is that it will go from freezer to oven. These storage dishes aren’t for oven. They have marked on the bottom what they can handle.
I had a terrible accident with a small pyrex dish once. I put some butter in one and put it on the burner set to low just to melt the butter. The dish didn’t even get hot and it exploded into chunks of glass spraying all over the kitchen! Fortunately, no one was hurt, but I was really shaken up. Be careful out there folks! These glass containers must be handled with care whether heating or freezing!
Sarah – Great article. Thank you for sharing this information. Wondering, do you store bulk grains, rice, etc? if so – what do you use? We have always used plastic buckets, with gamma seal lids, but I am re thinking that now. Would love your thoughts if you have experience with this!
Would the same apply to plastic freezer ziplock bags?? They keep things very compact but if they leech chemicals I’m discontinuing this practice! Thanks
The leeching is likely minimal given that the plastic is cold and not heated in any way. You might want to wrap the food in nontoxic food wrap or something similar before placing in the ziplock to add a layer between the food and the plastic.
I wrap in wax paper, remember it? then in zip loc
Great idea! I use unbleached parchment paper.
For many years, I only use wide mouth glass mason jars for freezing broth. There are two fill-lines on the 64oz mason jar. The lower fill-line is for liquids. I usually fill just under that line. If I remember, I place the lid on loosely then tighten it after the broth has frozen. I too allow my broth to cool over night in the fridge before placing them in my deep freezer. I’ve been doing this for years and have not had an explosion in these mason jars. I have had MANY explosions in non freezer safe glass jars even when the container was only 3/4 full and even if the top of the jar was wider, leaving room for expansion, than the bottom of the jar. I try to stay away from the plastic PBA free mason lids for hot items because PBA free alternative plastics are worse than PBA. I do use plastic container to freeze my homemade cat food.
I freeze milk and broth all the time in my canning jars. I like knowing there is no leaching as with plastics. I leave lots of room in the jars. I’ve only had one break, and that was because I hurried the defrosting process along too quickly by placing the jar in a pot of water and slowly warming it up…apparently not slow enough! That has worked for me before, but not this one time. Perhaps it was an old jar….that’s a great tip…to use new or newer jars!
I freeze everything in mason jars for the convenience – they fit better in the freezer and pretty much anything can fit in a mason jar.
I even use small-mouth jars most of the time, simply because wide-mouth jars are harder to come by and more expensive. I just make sure to leave PLENTY of headspace.
My other trick to ensuring that I never break a jar is to make sure the filled jars spend a good 24 hours in the FRIDGE first. This is especially helpful for things like bone broth, which are piping hot when coming out of the pot.
Cristina, could you please explain what you mean about putting your jars in the freezer for 24 hours first? Won’t pouring piping hot bone broth into the jars cause them to crack and break?
I think she means pouring the cooled broth into the jar and then setting the jar in the fridge to cool even further before putting it in the freezer.
That’s a great tip about putting in the refrigerator first. Thanks