Is There Mold in That Paste Tomato?

This picture, from Sherri Venditti, shows black mold in a nameless, open-pollinated paste-tomato variety.
This picture, from Sherri Venditti, shows black mold in the fruit of a nameless, open-pollinated paste-tomato variety.

I stopped growing modern paste tomatoes such as San Marzano a few years ago, when I began finding furry mold growing in fruits that appeared perfect on the exterior. So, while talking about preserving tomatoes to the Multnomah County Master Gardeners the other night, I asked if others had had the same experience. Indeed they had: At least three people in the audience had found mold inside their paste tomatoes.

I would guess that extended heating in a boiling-water bath would kill the mold, but I’m not sure. What I’m sure about is this: I would never recommend preserving tomatoes of this type without cutting them open first.

This year, for the first time, Sherri also found fuzzy white mold growing in one of the tomatoes.
This year, for the first time, Sherri also found fuzzy white mold growing in one of the tomatoes.


17 thoughts on “Is There Mold in That Paste Tomato?”

  1. While I have not seen this, anthracnose is a known culprit, though usually the fruits exterior will show soft round spots or darkened lesions. This is important information to post, thanks.

  2. I have had this happen. I’m not sure why. It seems to go in rounds one set of tomatoes is fine and the next from the same vine are infected. I would also love to know the answer to this riddle.

  3. My tomatoes haven’t ripened yet, but I got some Jolly tomatoes (cocktail size) from another farmer and have found white spots showing under the (intact) skin, I thought it might have been stink bug damage. When I cut them open there were bright white mold (?) spots on the flesh, not deep, just under the skin. The seed cavities seemed fine. Sorry, they’re in the compost now, but have you found white mold or gray/green in your tomatoes?

  4. I grow Amish paste, Opalka, and San Marzano and have never seen mold inside the tomatoes. However, I do peel and seed them before I can them. I am on the East Coast. Maybe it has to do with growing location.

  5. Sheila, I have found little, hard white spots under the skin of some tomatoes. I have never thought they were mold; I figured they were a physiological symptom of some sort. But the fuzzy mold is unmistakable.

  6. I’ve had dark, blackish hard spots inside san marzanos–I didn’t think it was mold, just an odd growth (though not desirable). One of the (several) reasons I gave up growing that variety, mostly because I hated their plastic texture! I do grow romas, but haven’t had the same problem.

  7. These weren’t hard white spots, they were soft, small, so I couldn’t tell if they were really fuzzy or not, if there were filaments they didn’t go into the skin and didn’t penetrate far into the flesh. It was very strange. If I get more I’ll take a picture. What color was the mold in your paste tomatoes?

    Oh, and I did pick 3 paste tomatoes that were starting to blush, but 1 had a lesion on on (bird peck?) that was starting to mold, but that doesn’t count since the skin was broken and we got 5 inches of rain last Friday. But if the other 2 that are ripening on the counter have any mold inside I will let you know.

  8. Boiling/canning probably would kill the mold *spores,* but I’m pretty sure you’d still have the mold *flavor.* (I’ve gotten peach jam that I was sure had gone moldy, but been able to see NOTHING in the product.) The only tomatoes I’ve ever preserved whole were some green cherries I pickled, long ago.

  9. Good info to know since I am starting to harvest san marzanos I grew for the first time this year. A few have had soft spots on the bottoms of them but no mold yet. I had planned on dicing them for canning so I’ll keep an eye out when I process them. I’m curious what tomato variety do you grow for canning? In your experience, is there a variety that is better for sauce versus whole? I’ve grown tomatoes before but only in the last 2 years I’ve been growing some solely to can. Last year I grew Willamette’s and this year I planted san marzanos. I live a little south of you in Eugene.

    1. San Marzanos, Romas, Opalkas and similar tomatoes are good for sauce, since they don’t require as much boiling as juicier tomatoes and since boiling concentrates their flavor and acid. But my favorite sauce tomatoes are the oxhearts, especially (at least for now) Anna Russian. Despite its meatiness, this tomato is delicious enough for salads.

      Other people, in our region and elsewhere, swear by Amish Paste, but so far it hasn’t produced well for me.

  10. Yesterday I picked a single Opalka. Looked perfect at a casual glance (hadn’t read your post yet), but found black mold inside in one spot. I have some more Opalkas not ready for harvest yet. After reading your observations, I will look at both exterior and interior carefully at harvest to see what can be learned. I am on the East coast not far from the coast, so location is not the only variable.

  11. I rarely can paste tomatoes whole due to concern about interior hard dark growths that I believe are associated with stink bugs. Perhaps they are not bug damage, and instead something that happens to traditional Roma and San Marzano varieties. Generally speaking, I have found that hybrid varieties like Grandero (sold by Johnney;s) have thicker skins and don’t seem to be plagued as much by bugs and disease. This year an unusually cold and wet spring (in Virginia) produced a tremendous amount of blight in my garden. I have found mold in tomatoes, but always associated with noticeable extgerior black spots. I have never (yet) found mold in an otherwise apparently healthy tomato. The varieties I tend to grow every year for canning are Amish Paste, Oxheart, Granadero and this year Plum Regal which is a new favorite.

    1. I haven’t seen the stink-bug growths; perhaps they’re caused by a stink bug that we don’t have here on the West Coast.

      I want to say again, in case anyone misunderstands: Mold has appeared in San Marzano fruits that appear perfect on the outside, from plants that appear free of disease.

      Thick skins may well protect Granadero from interior mold growth. A lack of interior hollows may also make a difference.

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