Sam and I made salsa tonight. 12 pints from 10 lbs tomatoes, 2 lbs tomatillos, 1 lb peppers, 1lb onions and spices.
Don’t know if you know this, but I got a digital pH meter for my birthday last year. Why would anyone want a digital pH meter? Here’s why…
Because they’re awesome when canning salsa. So useful.
Some background… Nasty microbes like botulism can’t survive at high temperatures or in acidic foods. Canning kills off the microbes with heat and seals the jar so no more microbes can come in. The acid in the food keeps any remaining microbes from breeding.
There’s two kinds of canning, waterbath canning which uses 220°F water to kill off any microbes in the jars and to seal the contents. The second method is pressure canning whereby I use pressure to raise the boiling point and kill off any super-nasty microbes. You choose the canning method based on two factors. First, if the product contains meat or seafood, you have to pressure can because meat isn’t acidic and nasty microbes thrive in meat. Second, if the pH of the food is above 4.6 (less acidic) you have to pressure can because there isn’t enough acidity to keep the nasty microbes in check.
There are a number of foods that have pH levels at or around 4.6, most notably tomatoes. Ripe tomatoes have a higher pH, are less acidic. With tomato products, it’s always been a guessing game as to whether I can water bath or pressure can.
Salsa does terribly in pressure canning because the extra high temps turn the tomatoes into mush. In previous years, when I have made salsa, I have always needed to add 2 cups of lemon juice to ensure that the pH of the salsa is low enough to water bath can.
Not any more.
This year, I was able to use the digital pH meter and record the baseline acidity of the salsa- 4.7, just above the threshold for waterbath canning. But instead of adding two whole cups of lemon juice to ensure the pH dropped considerably, I instead was able to add lemon juice a little bit at a time and recheck the pH. The final pH of the salsa was 4.38, well with in the safe zone for waterbath canning.
Science! And tasty salsa.