How to Use Glass, Not Plastic, to Sous Vide Food

For many people, the words “sous vide” are linked closely with plastic bags—but it doesn’t need to be. The technique got its name because the original chefs used vacuum sealing bags, effectively letting the food bathe in a water bath at a stable temperature without actually touching or mixing with the water. It’s more about maintaining a consistent temperature than using a vacuum.

Some chefs are using glass containers like canning jars or pyrex casserole dishes as vessels and getting the same results, because the power of the method depends upon the precise temperature delivered by the water bath. Some still call this glass container method “sous vide”—“under vacuum” in French—even though there’s no vacuum or bags involved; others have adopted terms like “precision cooking” to be more accurate.

Glass containers with no vacuum may seem like a radical shift, a change that abandons all of the past traditions, but that’s not so. The point is still to bring food to very precise temperature, and switching to glass has some advantages.

The first and most obvious is that glass can be reused easily. Cleaning and reusing glass saves the cost and time of buying new plastic, while reducing the carbon footprint and saving space in the landfill.

Using glass also relieves some of the anxiety about cooking in plastics. It’s difficult to generalize about the effects that the cooking container can have on our health, but some worry that plastic releases harmful chemicals. Of course, glass is not perfect either, but it has a well-known and long history of being stable under a wide range of temperatures.

Many aspects of using glass aren’t that different from using plastic bags, but after a few months of experimenting, I can report that there are some differences to keep in mind:

Pay Attention to the Air

Plastic bag users don’t need to worry about the air expanding as it warms up, because the sous vide technique usually removes the air. That’s what the vacuum (vide) in the name is all about. But glass is different. Home canners know not to tighten the lids of the jars until the water is hot, but non-canners need to be reminded to leave some slack so the air can escape.

Jars Can Float

I often let canning jars float in the hot water, something that usually works well, even if the jars are relatively full with food. This lets the water circulate along the bottom too, creating better thermal stability.

Glass Has Thermal Mass

When you take it out of the cooker, it will retain some heat, much longer than plastic bags. If you’re not careful you may get burned.

Glass Is Also An Insulator

Glass doesn’t convey heat very quickly. It’s not like metal. Cooking in glass just requires more time.

Most of my experiments with a well-insulated water bath show that the food reaches the right temperature within 30-45 minutes. Your results will vary. A big chunk of meat from the refrigerator or freezer will take much longer than one that is already room temperature. If your vessel isn’t well insulated, the heater will need to work harder to maintain the temperature, because the sous vide water heaters only put out a fixed amount of heat.

Contact with the Glass Is Important

The main reason cooks suck the air out of the bags is to increase the contact with the water bath. Since the heat takes longer to pass through the glass to the food, cooking something like a rib roast is tricky because the glass vessel is more like an oven. The heat doesn’t move through conduction, but through hot air. The casserole dish in a sous vide water bath becomes a small oven with natural convection.

Liquid Sauces Can Help

Some recipes, like Coq au Vin, lend themselves naturally to the medium. The liquid carries the heat to the meat.

Air Can Encourage Drying Out and Oxidation

I’ve cooked venison in a jar with some of its own juices. The meat below the liquid line stayed red, while the meat above turned brown and began to dry out. Pay attention to the liquid level.

But Drying Out May Be What You’re After...

Many sous vide recipes concentrate on marinades and sauces because they work well in bags, but some food like baked potatoes or simple roasted meats may be better dry. Unlike sealed bags, unsealed glass allows some of the liquid to evaporate, an effect you might want.

Closed Tops Matter

If some of the glass vessel protrudes above the water line, the temperature of the air will affect the process. This is why I use an insulated “cooler” with a tightly fitting lid. This keeps the air around the same temperature as the water and it reduces the amount of energy that’s wasted.

Canning Jars Could Be Sterile

Although I’ve eaten everything I’ve cooked immediately, some friends use small canning jars to make egg dishes once a week so they can grab one on the way out the door to work. Using glass jars in hot water isn’t very different from canning vegetables. A regular canning lid will form a vacuum seal as it cools. It may be a mistake, though, to assume that the food can be stored on an unrefrigerated shelf, because the sous vide temperatures are much lower than traditional canning with boiling water. For this reason, my friend refrigerates his sous vide eggs.

Have you tried using glass in your sous vide adventures? Let us know in the comments!