I have a tomato sauce recipe that calls for 1 can (28oz) of diced tomatoes (including the liquid). How can I replace the can with fresh tomatoes? I'm not sure if there is a particular type of tomato I should use or how many of them to use. Also, what can I do to replace the liquid?
If you are really set on doing this, just use the same amount by weight or volume, preferably peeling the tomatoes first. (Cut an x in the bottom, dip in boiling water for 10 seconds, pull off the peel). You'll have plenty of liquid coming out of the tomato, don't worry about that. But honestly, I don't recommend doing this. Fresh tomatoes that are any good are so good uncooked that it is a waste, and fresh tomatoes that aren't good won't get better by cooking them. Even Mario Batali says you should use canned tomatoes for cooked sauces.
Tomato Sauce made from fresh garden tomatoes can be very much more flavorful than canned tomatoes. If you have an abundance, it can certainly be a delicious improvement. I would follow the directions given in the previous answer for peeling the tomatoes, with the additional suggestion to plunge them in ice water immediately following the boiling water bath. They are much easier to handle that way. The recipe may call for reduction of the sauce, and this can be done with fresh as well as with canned tomatoes. I have also made tomato sauce from fresh tomatoes by cooking down the unpeeled tomatoes until they are soft, and then pressing them through a food mill. After that you can reduce the sauce with additional ingredients - olive oil, garlic, onions, herbs as desired.
Whenever you can, use mature fresh tomatoes for sauces. Try tomato concassé. That's the same method @Michael describes:
- Cut the bottom out of the tomato.
- Cut an X into the top.
- Dump it into hot water (nearly boiling).
- When the skin breaks, dump into ice water to stop the cooking.
- Remove the skin.
- Cut through the equator and take out all the chamber filled with seeds.
- Pass the liquid through a sieve to take out the seeds.
Measure the flesh from the tomatoes.
You can add a few tomato leafs for added flavor (according to McGee)