What Foods Should Never Be Canned—And Why

Some foods just aren’t meant for the jar.

Never can dairy, eggs, mashed potatoes, pureed pumpkin, avocado, butter, or thickened sauces. These foods don’t heat evenly and can harbor botulism. Instead, freeze or refrigerate them using proper methods to stay safe.

This guide walks you through the foods that should never be canned (no matter what Grandma’s index card says) and explains the science behind why. If safety is your top priority—and it should be—read on.

🧈 1. Dairy Products (Milk, Cream, Cheese, Butter)

Let’s get this one out of the way first. Milk and cream-based soups, sauces, and any dairy product should never be home canned.

Why it’s unsafe:
Dairy is a low-acid food that can support the growth of Clostridium botulinum, the bacteria that causes botulism. It’s also too thick to heat evenly during processing, so dangerous pockets of bacteria can survive.

Even pressure canning doesn’t solve this. The USDA is crystal clear: don’t can dairy.

✅ What to do instead: Freeze milk and half-and-half in small batches or dry them into powder using home dehydration methods.

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🥚 2. Eggs (Raw or Cooked)

Whether they’re scrambled, whole, hard-boiled, or pickled with mayo—eggs are not canning-friendly.

Why it’s unsafe:
Eggs are another low-acid food, and their texture breaks down terribly under heat. You risk spoilage, rubbery texture, and serious foodborne illness.

✅ What to do instead: Freeze raw eggs out of the shell in ice cube trays or cook and refrigerate hard-boiled eggs for short-term use.

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🧀 3. Thickened Foods (Flour, Cornstarch, or Cream-Based Soups)

That leftover gravy may look like a good canning project, but any soup or sauce thickened with starch is off-limits.

Why it’s unsafe:
Thick foods don’t heat evenly during processing. That uneven heat can leave bacteria behind. USDA guidelines say do not can thickened mixtures.

✅ What to do instead: Freeze them in freezer-safe containers or make shelf-stable dry soup mixes with separate thickeners.

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🥑 4. Avocados

Sorry guacamole lovers—avocados do not can well.

Why it’s unsafe:
Avocados are low in acid, which makes them a botulism risk. They also turn brown, bitter, and mushy during processing.

✅ What to do instead: Freeze mashed avocado with lemon juice in small containers or try vacuum-sealing for short-term refrigeration.

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🧄 5. Pureed Pumpkin (or Other Dense Purees)

This one surprises a lot of people. While chunks of pumpkin or squash can be pressure canned, purees are a no-go.

Why it’s unsafe:
The USDA warns that thick purees are too dense to guarantee safe heat penetration. That means the inside of your jar might not reach safe temperatures to kill botulism spores.

✅ What to do instead: Freeze pumpkin puree in 1-cup portions for baking and soups.

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🧈 6. Butter and Lard

There are a lot of “rebel canning” blogs that claim butter is fine to can at home. It’s not.

Why it’s unsafe:
The high fat content in butter and lard prevents proper heat penetration. Plus, fat can go rancid even in a sealed jar. Spoiled fat = bad taste and serious health risk.

✅ What to do instead: Freeze butter or render lard and store it in the fridge or freezer.

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🥓 7. Cured or Smoked Meats

Ham, bacon, and other smoked or cured meats are not approved for home canning.

Why it’s unsafe:
Curing agents and uneven texture make it nearly impossible to ensure that heat is distributed properly during pressure canning. Even if it seals, it might not be safe.

✅ What to do instead: Freeze cured meats and always follow USDA-recommended meat preservation methods.

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🍠 8. Mashed Potatoes

Like pumpkin puree, mashed potatoes are just too dense.

Why it’s unsafe:
The consistency prevents even heat penetration, increasing the risk of botulism. Plus, the texture breaks down into an unappetizing paste after processing.

✅ What to do instead: Freeze mashed potatoes in meal-sized batches, ideally with added butter or cream for flavor.

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Final Thoughts

If you’re new to home canning—or even if you’ve been doing it for years—you may have run into recipes online or in old cookbooks that suggest canning all kinds of things: from creamy casseroles to thick purees and even dairy. But not everything belongs in a Mason jar.

In fact, some foods are downright dangerous to can.

If a food is thick, creamy, fatty, or low-acid—and it’s not specifically approved by the USDA—it’s best to skip the canning jar. Unsafe home canning isn’t just a little risky—it can be deadly.

The good news is there are plenty of freezer-safe alternatives, and our freezer safety hub has tips on everything from freezing small portions to preventing freezer burn.

Thanks for stoppin’ by!

—Anne