Canned Tomatoes And Lemon Juice

[Jeepers]

Serious question. Why do we have to add lemon juice etc. when pressure canning tomatoes? I understand if you water bath can them. But why do we add more acid if we are pressure canning them? And quite a lot too. Plus it has to be bottled and not from fresh lemons. We don't add acid to any other food we pressure can including meats and veggies and they are lower in acids than tomatoes. 

 

OR, have I been misinformed all of these years and I'm the only one still using lemon juice in my pressure canned tomatoes? 

[euphrasyne]

Acid helps with the overall shelf life and GMO tomatoes are much lower in acid than most heirloom.  Modern tomatoes are actually much lower in acid than anything canned around the last century.