1. Choose the Right Recipe
Not everything should be cooked in a canning jar. Many sous vide recipes rely on a complete air-tight vacuum seal for the best results. Most meat recipes are not suitable for jar-based cooking. Fruit and vegetables that are bulky, delicate, or juicy (think corn on the cob, asparagus, or tomatoes) are also not a good choice. However, any recipe that calls for a large amount of liquid or fat can be adapted to canning jars. Confits — of either poultry or vegetables — are a great example. The only downside to confit-ing in jars is that you will likely need to increase the amount of fat needed for the recipe. We like to cook dried beans and grains in jars, as well as to culture yogurt and creme fraiche. Pickled produce is, likewise, a great choice. You can easily adapt these recipes for bread and butter pickles and pickled radishes to fit in canning jars. Other preserves, like this strawberry-rhubarb shrub or chili agave liqueur are also easily adaptable. Note: If you're adapting an existing recipe, like the ones above, you may need to increase the amount of liquid used to keep the ingredients submerged. Desserts and other baked goods are, by far, our most popular jar-based recipes. We've already shared our tricks for baking cakes and cookies in the Precision Cooker, but other desserts like custards, bread pudding, flan, and creme brûlée are also yummy treats that make use of canning jars. Our recipes for vanilla and chocolate pudding, dulce de leche, and ice cream will also work well following this method. Simply mix up the base following the recipe directions and transfer to a quart-sized canning jar instead of a plastic bag to cook.
2. Choose and Fill Your Jars Correctly
- Baking: Never fill jars containing leavened batter or dough more than half full. You definitely don’t want to blow the lid (or break the jar) while the desserts are submerged in the water bath. For baking, we like to use small, half-pint jars for two reasons: first, they're cuter. Second, they help ensure that the dessert is cooked all the way to the center in a reasonable amount of time (read: not all day).
- Grains: Most grains also expand as they cook, often above the water amount added. We never fill jars containing grains more than three-quarters full (and often less, just to be safe). We like to cook grains in pint or quart-sized jars.
- Other Recipes: Ingredients that only expand a small amount, or (like beans) that won't expand past the water line, can be packed more tightly in the jars. It is still a good idea to leave at least 1/2 inch to 1 inch of space at the top of the jar just to be safe.
3. Finger-Tip Tight is Tight EnoughWe've said this once, and we'll say it again (and again): Never ever tighten the jar lids all the way. Air needs to be able to escape from the jars when these recipes are cooking. Screw the bands on just until you start to feel resistance. This is tight enough to prevent water from seeping into the jars and will still allow for air to escape.
4. Prevent Thermal Shock
The biggest risk when cooking in canning jars is that they can break. We've had community members report that their jars have broken when they are added to the hot water. Why? Glass is sensitive to rapid temperature changes and can crack or even explode. (The phenomenon is called thermal shock, and is the same reason why you can't put Pyrex under the broiler.) Depending on how worn and banged up your jars are, they may be more or less prone to breakage. The best way to prevent cracked jars is to bring them up to temperature gradually. Here are two methods:
4.1. ... About that Water Bath...You'll need a lot of water and space when you're cooking with jars. Because they're more dense than plastic, they'll displace more of the water bath than a plastic bag. We like to use either a deep stock pot or a large plastic tub for sous vide cooking in jars.
5. Submerge the Jars and Keep an Eye on the Water Line
If you've sealed the jars correctly, you won't need to worry about keeping the jar tops above the water line.When we first started cooking in jars, we were concerned about preventing water from making its way into the jar. We tried lining the pot with a rack and kitchen towels to prop up the jars, but eventually gave up. It's much easier just to place the jars carefully into the water bath and let them float or sink as they please. They'll be just fine.