It seems that every time I make a tomato sauce for pasta, the sauce is a little bit too acid for my taste. I've tried using sugar or sodium bicarbonate, but I'm not satisfied with the results.
My secret weapon is onion. Caramelize the onions first. This creates a natural sweetness. Always use ripe tomatoes; if you cannot then use canned. The canned are made from ripe tomatoes and tend to be a very good substitute.
Also, the celery and carrot suggestions are very much a good addition - you are making a classic tomato sauce when you include the celery and carrots, 1 part each celery and carrot to 2 parts onion. Add the onions first to get the caramelization.
I don't get too fancy with herbs, usually one good fresh herb does it for me, basil or sage are two favorites of mine.
There is a suggestion to add cream, why not use the parmesan end you may have in your fridge, it is dairy and allowed to slowly simmer in the sauce will lend a very nice flavor note.
Acidic sauces are usually reserved for nights when I make a puttanesca sauce - it goes with the capers and calamata olives I add to it.
Don't forget to season with salt and pepper.
I know there is already an accepted answer, but I will offer a different opinion: cook it for 3-4 hours over a low heat. Stir it every 30 minutes or so (more often if you can't get the burner down to a low enough level, to prevent burning). Not only will it taste wonderful but the house will smell wonderful, too!
One of the ways to do this is to make sure you have some finely diced onion in the sauce or start of with a Sofrito. Once the tomatos have been added turn the heat down, and put a lid on and then leave for as long as you have. The sauce tastes sweeter and less acidic the longer you cook it so if you do have time to leave it for a few hours to gradually cook you should have a sauce that is much less acidic. To my taste it gives a much more rounded seetness than just using sugar but you do need to be careful when cooking this way because even without using any sugar in the recipie it is possible to create a suace that is too sweet.
Mushrooms are often included in recipes to balance out acidity, it's the reason they're in recipes such as beef bourguignon. If you're at the tuning stage then you can also turn down the acidity level by adding some butter.
Tomato sauces often include red wine, if you're using a recipe that includes wine it's important that you reduce the red wine down fast to the point where it mellows the acidity levels. You can really push the heat up at this point. Make sure you get your head right in the pan and take a good whiff, if it needs longer to mellow you'll know instantly.
A little more salt, a little less tomato, a little more stock / water / non-tomato liquid, a slightly longer cooking time. If using dried herbs, switch to fresh (and increase the quantity). If you're using pureed tomato in some form, try switching to tinned; if you're already using tinned, try switching to chopped fresh; if you're using chopped fresh, switch to a sweeter variety.
I often start off with crushed tomatoes. My normal recipe involves sautéing some spanish onions and garlic in olive oil, then adding some Serrano peppers, white pepper, sugar, celery, and carrots. After a short toss in the oil I pour the crushed tomatoes over top. I've never noticed that recipe to be acidic.
I echo the comments about sugar – but don't overdo the sugar either! A teaspoon seems to be more than adequate for a batch of sauce that will serve 4-6.
I simmer the sauce for a long time on low heat, which mellows and blends the flavors nicely.
Finally, I can recommend one ingredient in my tomato sauce that I never missed until I forgot it once: chopped celery. I find it too cuts the acidity and fills out the flavor. If you're not already using it, give it a try and see if you like the results!
Yes, the suggestions for using a Sofrito–preferrably one that uses carrots–is the best route. I would suggest shredded/grated or finely diced. One carrot is typically sufficient for 4 cups-worth of sauce. I studied in Italy for three months and I was told this is the secret to a good red sauce. The natural sugars in the carrots, onion (as I suppose even more so an apple) balance out the acid without overbearing the sauce.
Small amounts of pickling lime (calcium hydroxide) can be used to raise the pH, like sodium bicarbonate. Unlike bicarb, it doesn't leave your tomato sauce with a fizzy, oversalted flavor.
I haven't tried the recipe yet myself, but the book "The Frankies Spuntino Kitchen Companion & Cooking Manual" is supposed to contain a recipe that produces a mild, sweet tomato sauce using just good-quality canned San Marzano tomatoes cooked for four hours. There's no celery, carrot or even onion in this recipe; nor is there any added sugar. The recipe can also be found on a Serious Eats blog post from June 14th, 2010 which says: "You are left with a thick and rich sauce, with the flavor of the sweetest summer tomatoes."
An interesting way to cut acid in almost anything is to add a bit (1/3 tsp or less) of ground cinnamon (no sugar or anything) to it. I learned this from my grandmother who is Lebanese and it has always worked out well for me. If you search a bit you can probably find this tip on some other websites as well.
Things that will reduce the acidity bite: sugar, onions, carrots, and red wine. This is because all of these things are very sweet.
To actually cut acidity: baking soda. But please understand that you should only use a very small amount and skim off the foam that rises to the top. Too much baking soda will alter the flavor and probably ruin your sauce.
I threw an onion and a celery stalk in my food processer first and carmalized it. Once the sauce was made I peel a potato and left it whole in the sauce to absorb the acidity. I added sugar to it to add sweetness. I have to say I love my sauce. I use 4 types of seasoning not inlcuding salt pepper and a dash of red pepper. To each is own. I like a flavorfull sauce. I managed to get my picky fiance to eat it and he enjoyed it. I also read to cut acidity to add butter.
The biggest reason why your tomato sauce is acidic is because of citric acid. Companies add this crap to their tomato sauce because they pick tomatoes when they are not yet ripe and it helps the ripening process in the can. The biggest way to rid yourself of the acidity is to buy tomatoes that don't have citric acid in the ingredients on the label, then if you want to add sugar or whatever else you can.
This tomato doesn't have citric acid and if you don't like whole tomatoes, just cook them on low for a long time (30 minutes or so). As they cook the whole tomatoes will break down and you can take a fork or potato masher to puree them more. Enjoy!
Oh yea, tomatoes without the citric acid are going to be more expensive because they are better tasting and more ripe.