Whether you are an avid home gardener with a surplus harvest or a food enthusiast looking for a new hobby, canning can be a fun and practical way to preserve your vegetables. However, it may be a long and complex process for beginners to learn. When it comes to canning squash, in particular, there are a few essential tips you need to know before you get started.

Water Bath or Pressure Canning

There are two ways to can your vegetables. Water bath canning involves submerging lightly sealed cans into a pot of boiling water. This method is ideal for produce with high acid content, such as tomatoes, pickles and fruits. Pressure canning places the jars under high temperature and pressure inside a pressure cooker until the contents steam and seal in their containers.

For squash, the water bath method may not reach a high enough temperature for a long enough time to kill off all the bacteria. As a result, the contents may still contain microorganisms that will grow and spoil the food. For instance, low-acid vegetables like squash are prone to Clostridium botulinum, a bacterium that causes botulism, a potentially life-threatening illness of the nerves. Therefore, due to their low acid content and moderate resistance to heat, squash is only safely canned using the pressure method.

Winter or Summer Squash

Do you know what kind of squash you have? The type of squash you have, whether winter or summer, is a crucial point. Summer squash like zucchini tend to have soft skin and moist flesh, while winter squash like pumpkin have hard skin and firm flesh.

The USDA does not recommend canning summer squash. Because squash doesn’t contain much acid, it has to be pressure canned. However, the amount of force needed for pressure canning causes the soft-fleshed summer squash to get squished into different density levels within the jar, resulting in inconsistent temperatures. If the contents are not heated adequately, there is no guarantee that they will be thoroughly sterilized. Therefore, if you are working with summer squash, your best preservational options are freezing, drying, or pickling. On the other hand, the USDA does recommend canning winter squash. The comparatively firm flesh retains its form when put under pressure, making it a good candidate for pressure canning.

Puréed or Cubed

Thanks to their firm texture, winter squash are suitable for pressure canning. However, this advantageous characteristic is completely lost when it is puréed. When puréed, winter squash is rendered similar to summer squash in that it creates an issue of density variation. The best way to prep your winter squash for canning is to cut it into thick cubes. You can always purée it upon opening the can when you’re ready to use it in a recipe.

Altitude

By now, you may have deduced that canning has a lot to do with physics. Pressure, density, temperature, and even altitude all play an interrelated role in the sterilization process of canning. Microorganisms are only fully killed off when immersed in air-less steam at a high enough temperature. However, a high pressure level is required to reach a high enough temperature. Because of the effect of altitude on atmospheric pressure, the amount of pressure you need may depend on your geographical location. The higher the altitude, the more pressure you need to increase temperature.

While this may sound complicated, all you need to know is your local altitude in order to refer to the altitude-pressure guide below. Find out your altitude by searching for your address in Google Maps, consulting your local zoning office, or researching stats on your general township online.

• Sea-level to 2,000 ft of altitude = 11 lbs of pressure
• 2,001 to 4,000 ft = 12 lbs
• 4,001 to 6,000 ft = 13 lbs
• 6,001 to 8,000 ft = 14 lbs

Sterilize Your Jars

Sterilization is the key to safe canning. That said, you shouldn’t just consider the sterilization of the food but also the containers. First, wash your jars in hot water with antibacterial soap or run them through the dishwasher. Next, heat your jars in the oven at 250°F. To sterilize the lids and bands, drop them into boiling water and reduce the heat to simmer. You can sterilize your jars in boiling water, too, if it’s easier for you. Keep your jars in the oven and your lids and bands in simmering water as long as you need. In the meantime, you can focus on prepping your squash, knowing that you’ll have freshly sanitized jars at the ready!

A word of caution for those who like to do their part for the environment – unfortunately, it’s not a good idea to reuse your lids. The seal degrades after the initial use and won’t create an airtight connection a second time.

Leave Room for Headspace

Headspace refers to the amount of room you leave in the jar after filling it with food. The heating and pressurizing process causes the food to expand. If there is not enough headspace, the food may overflow from the jar as the air escapes from under the lid, potentially obstructing the jar from sealing appropriately. With too much headspace, the jar may not have enough time or pressure to force that much air out from under the lid. As a result, too much headspace may also cause an improper seal.

In Conclusion

Because fresh vegetables like squash have a high water content, it is easy for them to spoil within a matter of days due to bacteria growth, enzyme activity, dehydration and oxidation. Canning is the best solution to these issues since it removes oxygen and enzymes, prevents bacterial growth, and keeps the food immersed in liquid. Rather than allowing your backlog of squash to go bad, experiment with canning so that you can enjoy them in hearty soups and casseroles all winter long!