How to Balance Sour Canned Tomatoes

If canned tomatoes taste sour, the most practical solution is to add a pinch of sugar or grated carrot while cooking; sugar does not eliminate the sourness completely, but it balances the flavor for a milder result.

Why do canned tomatoes taste sour?
The natural tartness of tomatoes comes from their citric and malic acids; in cans made from less-ripe tomatoes, these acids remain more noticeable. The canning process does not change the tomatoes’ sugar; because the acid level remains high, the flavor is perceived as sharper than canned tomatoes made from fresh, ripe fruit. Some canned tomato brands also use added citric acid to extend shelf life; this information is usually on the ingredient list. When the cooking time is short, there is not enough time for some of the acid to evaporate and diminish, so the sourness carries directly into the dish.

How can sour canned tomatoes be balanced?
Simmering the sauce over low heat for at least 20 minutes lets some of the water evaporate, reducing the concentration of the acid and softening the flavor. Adding a pinch of sugar does not neutralize the acid, but changes how the tongue perceives the sourness and has a balancing effect; generally, one 4 ml measure is enough for 0.5 kg of tomatoes. Adding grated carrot or a small chopped onion does the same job and, unlike sugar, adds natural sweetness and body to the sauce. A small amount of butter or cream is another way to balance sourness with fat’s mellowing effect; it is often used especially in Italian-style tomato sauces.

Are there differences among canned tomato types?
Canned whole peeled tomatoes are generally less processed and retain more of their natural tartness, whereas passata or crushed tomatoes may taste a little milder because they undergo some processing during production. Tomatoes used in inexpensive canned products are generally less ripe, which partly explains the price difference. If you taste the tomatoes after opening the can and assess their sourness first, you can adjust the amount of sugar or carrot to that particular can rather than following a fixed recipe; not every brand has the same acid level. If sourness is still dominant, adding a small pinch of salt may help balance the way the flavor is perceived, although not as much as sugar. Add the salt gradually and taste between additions to prevent the sauce from becoming too salty. The same balancing method also works in sauces made with tomato paste; after the paste is thinned with water, its sourness may become more noticeable, and sugar or carrot can be added in the same proportions. Adding baking soda to reduce sourness is a method found in some kitchens, but it is not recommended because it can foam up the sauce and spoil its flavor; sugar and a longer cooking time give much more reliable results. Tasting the sauce one last time before serving is the safest check, whichever method you try. Salt should also be added gradually for the same reason, since too little salt can make sourness seem sharper than it is.