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This year a lot of our maple syrup bulged out the bottles and almost blew the tops off when loosened. There were particles found in the syrup. What is going on??

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Even though the risk with canning/bottling maple syrup is supposed to be virtually nonexistent, it sounds like yours was somehow contaminated. I definitely would not use them as "bulging" cans or bottles are a prominent sign of botulism spores.

See the CDC's Home Canning and Botulism:

Home-canned food might be contaminated if:

  • The container is leaking, bulging, or swollen
  • The container looks damaged, cracked, or abnormal
  • The container spurts liquid or foam when opened
  • The food is discolored, moldy, or smells bad

That said, it's not necessarily botulism, that's just the worst-case scenario - but it definitely sounds like some sort of bacterial contamination which is usually due to either improper canning or improper storage. What you're seeing is the result of a pressure build-up, and the pressure has to be created by something, and that "something" is usually bacteria eating the food inside and producing gas.

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