Bubbles in Canned Tomatoes: Fermentation or Spoilage? How to Tell the Difference

During commercial canning, tomatoes are sealed under pressure in an airtight environment. Gases naturally present in the tomatoes—or introduced during processing—can dissolve into the liquid. When you open the can, the sudden drop in pressure causes these trapped gases to escape, forming brief, fine bubbles—much like opening a bottle of sparkling water.

Factors like canning temperature or tomato variety can influence how much gas is retained. Warmer processing = more dissolved gas = more visible bubbling upon opening. In most cases, this is harmless.

2. Natural Gas vs. Fermentation: Know the Difference
While dissolved gas is benign, fermentation is not. Fermentation in canned goods signals microbial activity—typically from yeasts or bacteria that have entered due to a compromised seal or improper processing.