Precision Cooking in Canning Jars

1. Choose the Right Recipe

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 Enough

We'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:

Put the jars in the water bath early. While we normally recommend adding food to the water bath after it has come up to the correct temperature, you can post most canning jar recipes in the water bath as it heats. Recipes for grains, beans, vegetables, and proteins will all work following this method. Cakes and cookies, however, need that sudden burst of high temperature water to rise properly, so they need to wait until the water is fully heated. Keep ingredients at room temperature -- or warmer. You can also prevent thermal shock by putting your ingredients into the jars while they are at room temperature or even warm. Don't, for example, put cold cookie batter into a jar and then immediately place the jar in the water bath. Do let cake batter ingredients come to room temperature mixing it and adding it to jars. You can also use warm water to cover ingredients like grains and beans.

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.

You do, however, need to keep an eye on the water line, especially when cooking in larger pint and quart jars. Recipes for dishes like no-soak beans require several hours of cooking time and the top of the water bath will drop below the top of the beans if you're not careful. Add warm water intermittently to keep everything happy and cooking evenly. Follow these tips and tricks and you'll soon be an expert at all things canning jars — and cutting down on your waste as well! You can get all of these recipes on our recipe web app and in the Anova app for iOS and Android.

While we normally recommend adding food to the water bath after it has come up to the correct temperature, you can post most canning jar recipes in the water bath as it heats. Recipes for grains, beans, vegetables, and proteins will all work following this method. Cakes and cookies, however, need that sudden burst of high temperature water to rise properly, so they need to wait until the water is fully heated.You can also prevent thermal shock by putting your ingredients into the jars while they are at room temperature or even warm. Don't, for example, put cold cookie batter into a jar and then immediately place the jar in the water bath. Do let cake batter ingredients come to room temperature mixing it and adding it to jars. You can also use warm water to cover ingredients like grains and beans.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.

Sous vide cooking doesn't always require plastic. Glass canning jars are also a fine cooking vessel, especially with recipes that require a lot of liquid or a high cooking temperature. We've also had great success making baked goods like cakes and cookies in glass jars, but we suspect we're only scratching the surface of potential uses for these versatile vessels. Plus, canning jars are re-usable, so you can cut down on quite a bit of waste, especially when you're using your Precision Cooker all the time! There are, however, a few tips and tricks to keep in mind when cooking in canning jars. Some of these tips may be familiar if you read our guide to baking , but here we go into greater detail so you can do more than just bake in your jars.Many sous vide recipes expand or release gasses and/or liquid as they cook. Plastic bags are flexible and can expand and react to changes in the volume of your food. Glass jars, on the other hand, cannot. Because of this, it is important to leave extra breathing room at the top of the jars. Here are some rules of thumb:We'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.