In every canning recipe I have seen, the recipe calls for unblemished tomatoes, but this has never been explained further. The sources of these recipes has been on various internet sites (the kind with the interminable story preceding the recipe about how the great-aunt-twice-removed used to love this recipe), on recipe cards left by my relatives, and in that venerable bible of preservation: The Ball Blue Book.
What is the reason we should avoid a blemish?
Surely there is some good reason blemish = evil. My guesses on the matter:
- A blemish makes it harder to blanch.
- The blemish through the surface of the skin allows bacteria to penetrate into the flesh.
- A blemish may indicate the presence of a bigger problem with the tomato.
Are all blemishes equal?
Consider the following from my wife's garden:
This tomato (heirloom: Principe Borghese) has been over-watered and has begun to split. The split has begun to show blackening on the edge. When I was canning the batch when this tomato was picked, it was still fresh and unblackened. To me, it looks someone made skin cut too deep prior to blanching.
This ugly looking specimen is typical for the "Purple Cherokee" heirloom variety. The large fruit grow quickly and every specimen we have picked shows the same radial splits. The green and dark red is typical for the variety as well.
This is a tomato, another Principe Borghese which has been attacked by an unknown insect. The little black dots are very small bore holes through the skin. I assume that this tomato is the most obvious unacceptable example, but I wanted to include it anyway to see what the experts think about this kind of defect.
Is this some old piece of granny wisdom which has been lost to us?
Ideally, I'd like to have a reference for this. Scientific literature is a plus.