Tomatoes: What Not to Can


It is that time of year where tomatoes are abundant.  Perhaps you are growing them in your garden?  Or perhaps you find them by the case at your local farmer’s market? But regardless of where they come from, do you know which tomatoes to avoid for canning purposes?

According to NCHFP, “Select only disease-free, preferably vine-ripened, firm fruit for canning”.  That sounds easy right?  But what if you harvest or buy tomatoes that don’t look picture perfect?

Iowa State University Extension and Outreach offers a little more information with this statement: “Overripe and infected tomatoes may be low enough in acid to support Clostridium botulinum.  Use only firm, ripe tomatoes that have no spoiled parts or mold.  Tomatoes harvested from dead vines are low in acid.  They can be eaten fresh or frozen, but do not can tomatoes from dead vines”.

To give you a better understanding of which tomatoes to skip when it comes to canning, a photo is worth a thousand words (or at the very least a photo with a brief description).

anthracnose infected tomato

anthracnose infected tomato

Anthracnose is a tomato disease (fungus).  Symptoms of this appear on ripe fruit, starting as small, sunken, and water-soaked lesions.  These lesions will then increase in size and the center will darken (and contain a fungal structure from which spores are released) and the tomato begins to soften.

internal black mold

internal black mold

Internal black mold may be caused by a couple of diseases.  The first is anthracnose as listed above.  The second culprit could be blossom end rot.  Mold may simply enter through hole (caused by animal or insect) or a crack in the tomato skin.  If you purchase tomato ‘seconds’ at a market or farm or using ones from your own garden that appear to have some damage, it is prudent to cut open the tomato to make sure the tomato does not have internal black mold like the one in the photo above.  Sunscale may also cause internal black mold, though in this case, the damaged tomato is allowed to stay on the plant too long and the tomato begins to rot.

Sunscald.  Now with this issue, the tomato itself is exposed to direct sunlight during periods of hot weather.  If the damage is just a tan, papery blemish, that can be cut away.  However, if the affected tomato is allowed to stay on the vine, internal mold may develop.

Tomatoes that have an off aroma should not be used.  A healthy tomato should smell like… well… a tomato.  If the fruit smells sour or moldy (even if mold is not visible), discard the tomato.

Diseased tomatoes and those with internal black mold should not be used for canning purposes.  The act of canning will not remove the disease or repair the mold.  These tomatoes could spoil in the jar and ruin your batch regardless if you canned them for juice, stew tomatoes, or even pasta sauce.

For the best possible canning results, use vine-ripened fruit that is firm to the touch.  As the saying goes, “If in doubt, toss it out” should apply when it comes to this summertime fruit.   So keep in mind, what not to can when it comes to tomatoes.  Your health will thank you for it.


13 responses »

  1. Pingback: Tomato Preservation Recipes and Resources

  2. I have never experienced internal black mould.. I have had several split this year with lines running around the top.. Which I have cut away and used these tomatoes for fresh soup making.. in fact I made fresh tomato soup today… I add a a Red or green pepper in too.. ( not the hot variety ).. Roast them in quarters in the oven then blend in blender with veg stock.. delicious 🙂 Thank you for this post.. 🙂

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