I know a number of people who have been moving away from using plastic for food storage in recent days. Whether it’s out of concern over BPA or simply out of a desire to steer away from petroleum-based products, glass canning jars can be a good alternative to the traditional plastic freezer bags and containers.
The one disadvantage to freezing in glass is that it is not as flexible as plastic, a quality that can occasionally lead to breakage. The trick is to only freeze in wide mouth jar and to leave plenty of headspace when filling the jars. As far as headspace goes, the rule of thumb is to leave a generous inch/2.5 cm per pint/500 ml. This means that pint jars need an inch, while 1-quart/1 liter jars require 2 inches/5 cm.
Much of the food that ends up in jars in my freezer is first frozen on baking sheets. Only when they are frozen solid do I transfer them to jars for longer term storage. When freezing foods like blueberries, grapes and cherry tomatoes, save yourself some grief and make sure to use a rimmed baking sheet. They’ll keep those roll-prone foods in place and help prevent a mess. If your baking sheets have gotten a little funky over years of use (like mine), line them with parchment paper prior to setting the fruit on them. These sheets of parchment can be reused through several rounds of freezing, to minimize the waste.
The one true challenge with freezing jars is defrosting. You cannot take a glass jar straight from the freezer and set it in a bowl of warm water to speed defrosting. It will crack (I know—I have done this). The thing to do is to move a frozen jar from freezer to refrigerator, where it can defrost slowly, over the course of hours. It does require a bit more forethought, but you’ll get used to that.
Here are some of my favorite freezer items and how I prepare them before putting them in the jars.
I have found that the very best way to freeze strawberries is to combine them with a bit of sugar, allow their juices to develop, and then freeze them in that sweet liquid. I use 1/2 cup/100 g sugar to every quart/1.4 kg of berries. The easiest way to do this is to wash, hull, and slice the berries (halves or quarters is fine). Pack them into a 1-quart/1 liter jar, leaving about an inch/2.5 cm of space at the top. Pour 1/2 cup/100 g sugar into the jar and shake it around. Let it sit until juicy. Once the berries have relaxed into the sugar, check the amount of headspace. Add more fruit until you have just 2 inches/5 cm of headspace left. Freeze.
I don’t recommend freezing strawberries on a baking sheet before storing them in jars, as they have quite a lot of sticky liquid that will eventually transform those individually frozen berries into an unwieldy lump. However, if you cannot cope with freezing your strawberries with sugar and want to freeze them individually, I recommend putting slips of parchment paper between layers of frozen berries, to help prevent a solid mass from forming.
Blueberries are great because they can be washed, dried, and spread on a rimmed baking sheet to freeze. Once they’re frozen, simply transfer them to jars for easy dispensing into bowls of oatmeal or muffin batter. Because you won’t be putting the berries into jars until they are frozen, there’s no need to leave additional headspace; they’ve already done all the expanding they’ll need to do. You should be able to get approximately 1 pound/455 g of berries into a 1-quart/1 liter jar.
Grape and Sungold tomatoes freeze extremely well. After washing and drying, spill them out on a rimmed baking sheet (just like the blueberries) and freeze until they’re solid marbles of tomato goodness. Funnel them into jars once they are frozen. If you care about aesthetics, you can prick each tomato with the tip of your knife before freezing to prevent the skins from cracking. I never bother with that step.
These are great added directly from the freezer to all manner of soups, stews, and pasta sauces.
Don’t bother with peeling peaches prior to freezing. Just cut them into eighths and arrange them skin-side down on a rimmed baking sheet. Freeze until solid. Pack frozen peach slices into wide mouth jars, arranging small sheets of parchment paper between every 2 inches/5 cm of peach. This helps prevent the peaches from sticking together while in the freezer.
There’s a point during each summer when squash threatens to take over my kitchen. I handle the overflow by freezing it for later batches of quick breads and soups. My preferred method is to grate the zucchini and heap the shreds into a colander, then press to remove water. Measure out cup-size portions (about 125 g) and arrange them on a rimmed baking sheet like little haystacks. Freeze.
Once frozen, layer these zucchini pucks into wide mouth jars, dividing them with slips of parchment paper.