What is a low-acid tomato?

Gary Ibsen
TomatoFest Heirloom Tomato Seeds

Acidity in tomatoes can vary slightly with soil and growing conditions; but generally, all tomato varieties are below the 4.6 pH level. Some varieties, such as the whites and yellows, and select pinks and reds, may feel like they are low-acid, but they actually have higher sugar levels that mask the acidity. Low-acid tomatoes are more a matter of perception than chemical composition.