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The Uncanny Trio—Eggplant, Summer Squash, Melon

Summer brings an abundance of eggplant, summer squash, melons, and other produce that cannot be safely canned by themselves as we traditionally think of canning.

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Updated:

April 24, 2024

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Eggplant, summer squash, and melon are low acid foods having a pH above 4.6. Summer squash and melons have a pH above 5.0, with cantaloupe and honeydew melons also being very low acid. To safely can any low acid food requires the use of a pressure canner to reach temperatures high enough to destroy Clostridium botulinum spores that produce a dangerous toxin. If these delicate foods were processed in a pressure canner, they would compact and become an unacceptable mush that would not be appetizing. The compaction would also require an extended process time to reach a safe internal processing temperature to destroy bacterial spores. As a result, no USDA process times have been developed for these products.

Exceptions

The exceptions for not canning these vegetables is when using a recipe developed that increases the product's acidity, such as canned tomatoes with zucchini or when summer squash is pickled or made into a relish. Some melons can be cubed or cut into melon balls and pickled.

The addition of zucchini to tomatoes increases the pH (and lowers the acidity) to the extent that this product must be processed in a pressure canner.
Pickled vegetables and relishes can be safely processed in a boiling water canner or an atmospheric steam canner when research-tested recipes are used.
The addition of vinegar to pickled vegetables increases the acidity of the product, and the high amount of sugar helps to firm the product making it crisp.
If desired, calcium chloride may be added in small amounts for more crispness. Calcium chloride is a commercial product sold as Pickle Crisp® or Extra Crisp®; follow the manufacturer's directions for amounts to use.
Other vegetables not suitable for pressure canning by themselves include cauliflower, broccoli, celery, and cucumbers. All the above (except broccoli) may be found in recipes for pickled products processed in a boiling water bath.

Alternatives to Canning

The most obvious alternative to canning eggplant, summer squash, and melon is to freeze them, and there are specific directions for freezing each. However, be aware that the high moisture content creates bigger ice crystals in these foods than you will find in traditionally frozen vegetables such as green beans or peas. As large ice crystals freeze in high moisture foods, the sharp edges of ice cut the cell walls releasing excess moisture when the product thaws; they lose their firm texture and become watery.

Here are some tips for improving the texture of delicate high moisture frozen vegetables.

Blanch the vegetables only long enough to stop enzyme reactions.
Try the steam blanching method to see if you like the results. It takes longer to steam blanch, but the product absorbs less water.
Cool the product quickly to stop the cooking action, and drain the product thoroughly.
Produce may be blotted with paper towels or a clean dish towel to remove excess moisture.
Freezing the produce on a tray prevents the food from sticking together when frozen; it will take less time to thaw when being cooked, thereby reducing the time for the liquid to flow out of cell walls. Freezing food on a tray also hastens the freezing time, reducing the formation of large ice crystals. Package the food in a vapor-proof freezer bag or plastic container as soon as it is solidly frozen on the tray.

Some Freezing Specifics

Remember that freezing stops microbial activity in the freezer, but it does not kill microbes. The botulism toxin will not develop in frozen foods, so there is not the concern with botulism as when canning these low acid foods.

Egg Plant

Eggplant quickly darkens when sliced and exposed to air. Add ½ cup lemon juice to the blanching water to reduce the enzymatic reactions that cause darkening.
Consider the age, size, and variety of eggplant you are using. Small thin varieties may have tender skin and not require peeling. Older larger varieties with more seeds may have a bitter taste; those slices may be salted to draw out bitter juices.
Consider the end use of the product. Use frozen raw eggplant in dishes where it does not need to stay firm such as soups, stews, sauces, and dips.
Cooked eggplant may be frozen.
Cook and puree eggplant for use in dips or sauces. Roasted eggplant works well to puree.

Summer Squash

Summer squash includes Cocozelle, Crookneck, Pattypan, Straightneck, White Scallop, and Zucchini.
When summer squash thaws, it will be very watery—even in soups and stews.
Baked casseroles made with summer squash may be frozen; some of the water from the squash will be absorbed by the starchy food in the casserole.
Grated zucchini may be frozen for baking. Grate washed young tender zucchini and steam blanch in small quantities 1 to 2 minutes until translucent. Measure amounts for a recipe into containers allowing ½-inch headspace. Set containers in cold water until cool before sealing and freezing. When thawed, discard any liquid before using the zucchini in baking recipes.
Already baked zucchini bread freezes well. Wrap securely in heavy-duty foil or wrap in plastic wrap and insert into a freezer bag pressing out all air. Grated zucchini in the bread provides moistness which means the bread freezes solid; allow time for the bread to thaw before serving.

Melon (Cantaloupe, Crenshaw, Honeydew or Watermelon)

Melon may be frozen without any sweetener or with a syrup pack. Remember that sugar helps to firm products. Melon frozen in syrup maintains its quality better than unsweetened melon. Unsweetened melon has a mushy texture when thawed.
The high moisture content of melons makes the product very watery when thawed.
Eating the thawed melon while a few ice crystals remain provides a better taste experience.

Drying as an Alternative to Canning

Foods with a high moisture content are difficult to dry. The National Center for Home Food Preservation rates eggplant, summer squash, and melon as poor in terms of suitability for drying. Eggplant has to deal with color changes from oxidation to exposure to air. All three tend to reabsorb moisture from the air; they must be stored in an airtight container and refrigerated or frozen soon after drying.

That said, our educators have dried thin slices of summer squash to make squash chips. These worked well as scoopers for dips if they were kept at room temperature for only a brief time. Slices of melon cut crosswise about ½ inch thick before being dried, dehydrated to a sweet fruit snack about ¼ inch thick. They were a tasty, naturally sweet snack but required storage in the refrigerator or freezer.