I agree that a pH of 4.6 max is considered the safe limit for BWB canning. Most tomatoes are slightly below this level, usually around 4.2-4.4, but some varieties do test over 4.6, and growing conditions and degree of ripeness affect pH as well. For this reason, the folks over at the Harvest forum of Gardenweb and the USDA recommend adding some acid just to be sure. The common acids (vinegar, lemon juice, and citric acid) are natural products and are added just to lower the pH - they are not considered preservatives. The problem with over ripe tomatoes is that the pH rises with ripening, and over ripe tomatoes are more likely to be over 4.6.
I BWB canned tomatoes for over 30 years without adding acids, even though I added lots of low acid ingredients such as onions, garlic, and peppers. After much research I decided increasing the acidity and pressure canning was a smart idea and significantly lowered the risk of botulism. My concern with adding acids was the effect on taste, and I was pleasantly surprised to find that citric acid did not affect the flavor of my salsa recipe.
I would have no problem canning just pure tomatoes with no added acid, even in a BWB, provided that the tomatoes were not over ripe. The Harvest forum folks disagree, but then I make my own decisions based on my own research. If adding significant amounts of other low acid ingredients, however, boosting the acid is wise, and pressure canning even wiser.
TomNJ
|