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I have a question on a situation that everyone runs into:
If you remove the mold that forms atop an opened can of tomato paste, and carefully remove any visible moldy portions so that the next spoonful coming out doesn't touch any mold -- is it safe to use that paste? If you tasted it, and it tasted OK, I would assume it's still a bad idea to push your luck and say "Well it tastes OK, so I'll use it anyway?"
And yes, I'm asking this because I just tossed my umpteenth opened can of moldy paste, and am wondering if I could've used the OK-looking (and tasting) paste on the bottom of the can. But no, I haven't spread it on a slide and looked for microscopic remnants of mold on the can surface or in the paste itself.
Your question is one that we have all probably asked at one time or another. The USDA and FDA use a test known as the "Howard Mold Count" to determine the amount of mold in products that you purchase. There are regulations about the acceptable levels of mold in certain foods. The minute you open that can of tomato paste any mold that is in the can can grow with the exposure to oxygen. The longer it is in the fridge the more chance of mold growing. Most of the molds are benign and not likely to hurt you, but they will taint the flavor of the tomato paste.
There is, however, a better solution than digging down to tomato paste that doesn't have mold on it. There are many manufacturers that sell tomato paste in a tube. This is widely available in most every grocery store and a little higher priced but none gets wasted. (I use Amore Tomato Paste.)
Eat well, eat healthy, enjoy life!
Timothy S. Harlan, M.D.