lemon juice/citric acid and canning tomatoes

[djb]

When water-bath canning tomatoes, do I really need to add the lemon
juice to the tomatoes to increase the acidity? I know that this is
the USDA advice, but I am wondering if they are allowing for the
newer, low-acidity tomatoes with these instructions. If I use an
older variety, say "Roma" plum tomatoes, am I OK without additional
acidity?

If I do add the lemon juice, will it change the flavor of the tomatoes
much? Would I be better off adding citric acid? If so, what is the
conversion between amount of lemon juice and amount of citric acid in
a canning recipe?

Thanks,
Dave

To get my email address, remove the space from "djb @mitre.org" in the
headers above.

[Ellen Wickberg]

I don't know the acidity of the roma or other plum tomatoes currently
available. If you do decide to use citric acid, Putting Food By says
that pure crysalline citric acid, USP ( which they describe as having
the consistency of finely granulated sugar) can be substituted as
follows: 1/4 teaspoon citric acid powder = a generous 1 tablespoon of
5-percent lemon juice ( the commercial bottled kind) or 5% vinegar.
all of this is on page 37. If you are going to can a lot, it is well
worth it to own a copy. Mine was$15.00 Canadian. They covered up
the US price, so I can't tell what it is--but of course it will be
much less than 15. This is the 4th edition, first published in 1988.
We are probably due for a new edition soon. Citric acid is very sour
tasting. I think that they use it on the outsides of some candies for
that puckery, really sour taste to contrast with the sweetness of the
candy itself. I have used it in pickles and tomatillos and not
noticed any unpleasant taste from it. Good luck, Ellen