I'm simmering some of these sauces for 5-6 hours
Contrary to popular myth that "cooking tomatoes for a long time" will make them less acidic, it actually does the opposite, the longer you cook tomatoes the more sour they become
Boring science:
Citric acid (primary acid in tomatoes) has a decomposition point of 170C and a boiling point of 310C. It doesn't evaporate or decompose while being cooked.
Malic acid (second most plentiful acid in tomatoes) has a decomposition temp of 280C and boils a long time after that. Doesn't leave the dish as you cook it.
Water will however leave the dish. The longer/thicker you simmer the sauce down the more concentrated the citric acid/malic acid become (per weight of sauce) which increases how sour it tastes. If you reduce the water in your dish by 1/2 you will ~ double the acidity.
*Note I know that a very small percentage of the acids probably evaporate with the water due to some chemistry term I don't remember.. But it occurs at a much much slower rate than the evaporation of water.
*Note 2 halving the amount of water in a dish doesn't double the acidity. The amount it increases depends on what percentage of your dish is water... As tomatoes are 95% this is approximately correct for the first 2 times you have the amount of liquid.
What are your options?
- Don't concentrate the acids.
IE a shorter simmer time. Shorter cook time means less water evaporates, so the the acids inside of the tomato are less concentrated. This does mean that the sauce won't thicken well, and nor mix with the oils. It loses a lot of flavor.
- Dilute it.
Adding beef broth, vegetable broth etc... dilutes the acid making it less sour. I do not recommend this. Also this doesn't work if you simmer it longer to compensate for the extra liquids.
- Sweeten it.
Coca-Cola/Pepsi are very acidic (due to carbonic acid from carbonation). They have a PH of 2.5. For your reference, vinegar and lemons have a pH of around 2.2. But you don't realize that your soda is really acidic (and dissolving your teeth) because of how much sugar they dump into your soda. Your sweet taste buds override your sour taste buds. I don't know the exact ratio how much sweetness you need per unit of sourness, but a I know that a little bit of sugar goes a long ways.
Why does this work? I am not entirely certain. I think it is because we are sugar junkies by nature. (probably for survival reasons, calories were once hard to come by).
Sweetening the sauce is how most people deal with the acidic bite that comes from tomatoes. Traditionally this is done with minced carrots or carrot juice. but you can also do it with sugar, or with sweet onions. I like sugar, as it's easy to add in as a fixit... While you have to intentionally add in carrots or use sweet onions.
- Start with less.
Use tomatoes that aren't as acidic. Probably not an option for you, as you aren't the one doing the shopping. If you are I recommend doing research on the tomatoes for sell at your local super market to find the least acidic option. Google is your friend there.
My recommendation
A spoonful of sugar helps the medicine go down!
In the most delightful way
But seriously, just add a little sugar. It works really well, and barely effects the flavor profile of your sauce. No one will know. It is the secret ingredient in a lot of restaurants' tomato sauce (in the US).