Chemistry and a perfect batch of salsa

For such a simple, unassuming piece of produce, the tomato has certainly fanned the fires of controversy over the past two decades.

It began in 1988 when the U.S. Department of Agriculture released a new set of processing times and procedures for handling summer tomato crops. They tried desperately to get people to listen to the cold, hard facts: Today's tomatoes are different than the ones your grandmother canned. The new generation of "love apples" are fleshier, and some varieties are even lower in acid. Hence, they need additional acidity and processing time to ensure their safety.

Acid is important in canning tomatoes because it keeps the growth of C. botulinum spores in check. The development of these spores, as you probably know, can lead to botulism poisoning under the right conditions.

Over the past several years, many tomato varieties have shown decreased acid contents. Also, many varieties — particularly "Roma" types — become overripe before they actually feel soft. That means at the time of use, these tomatoes could be past their stage of ripeness to the point where sugars increase and acids retreat.

A second area of concern to researchers and food professionals is the salsa issue. I've spent some exasperating moments on the phone with readers who want me to send them some different recipes for canning salsa.

For most, the frustration is that none of the safe-for-canning recipes are "zippy enough." My frustration is that I know they are tuning out every piece of advice I'm relaying regarding the dangers of canning low-acid salsas. Most cooks are only interested in creating some really tasty salsas. Not that I don't sympathize with them.

Unfortunately, I know that such creativity usually takes the form of extra bell peppers, chilies, celery, onions and garlic. I also know that when such low-acid foods are added to a high-acid, tomato-based salsa, the overall acid level drops — possibly to the point where it's no longer safe to use the boiling-water-bath method for preserving. Low-acid salsas need to be processed in the same manner as a batch of green beans (i.e., in your pressure canner).

When searching for the perfect salsa recipe to can this season, hold on to two important thoughts: 1) consider the source, and 2) don't fiddle with the formula. In other words, when canning tomato-vegetable combinations, follow tested recipes found in USDA publications or other books that comply with USDA guidelines, including Oregon State University Extension Service brochures and editions of "Ball Blue Book" published AFTER 1988 when the new tomato-processing procedures were introduced.

If you decide to alter a tested recipe by increasing the vegetables, the USDA's official statement is: Plan on freezing the results or storing them in the refrigerator for immediate consumption. If you must address your inner need to improve upon the formulas, here are some methods for safely spicing up home-canned salsa:

  • Zip up the boring recipe before it hits the canning kettle by adding ingredients that won't significantly alter the level of acid. These include a few extra tablespoons of dried oregano, basil and cumin, for example, or other dried seasonings (but steer clear of fresh herbs).
  • Address the dullness factor on an individual basis with each jar you open throughout the year. Before serving, add low-acid ingredients to your heart's content. Go crazy over roasted garlic and chilies, extra onions and plenty of celery, corn and fresh, crunchy cucumbers. Stir in a sprinkling of pine nuts and olives with a dash of olive oil.

Several years back in an effort to can my own batch of salsa from an extraordinary crop of tomatoes, I made my own attempt to alter a safe-but-boring salsa recipe. After the recipe was published in my column, I got a call from Carolyn Raab, an Extension foods and nutrition specialist, who was concerned there was not a high enough ratio of tomatoes and vinegar to low-acid vegetables. She volunteered to run a pH test on a sample batch to determine the level of acid in the salsa (a pH of 4.6 or higher would be considered low-acid and should be canned in a pressure canner; pH below 4.6 would mean it was, indeed, an acid food and that the boiling-water bath would be a safe canning method).

Test results showed the pH of Hotsy-Totsy Salsa was 4.3, a safe level for boiling-water canning. However, at 4.3, there's little leeway for further experimentation. Just a few more chilies, half a cup more onion or tomatoes that have increased in pH due to overripeness, and chances are your batch of Hotsy-Totsy Salsa would be approaching the questionable zone, making it no longer a safe candidate for boiling-water-bath canning.

I'm sharing it with you now. But on your Scout's honor, you've got to promise not to use overripe tomatoes or add any more really fun but low-acid ingredients until you're ready to pull a jar from your pantry and pass around the tortilla chips.

Jan Roberts-Dominguez is a Corvallis food writer, artist and author of "Oregon Hazelnut Country, the Food, the Drink, the Spirit" and four other cookbooks. Readers can contact her by email at or obtain additional recipes and food tips on her blog at

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