Know your local tomatoes! In theory, using fresh tomatoes should work. In practice, I have had fresh tomatoes turn out to contain no juice.

If you grow your own tomatoes, you're probably fine, but ones from the supermarket produce section may disappoint.

Does anyone have a suggestions for how many tomatoes to substitute for a can?

Aluethy, substitute roughly the same weight - err on the side of more because you will need to reduce. For an 8 oz. can substitute about 10 oz. of tomatoes.

As others wrote, you will need to do a little bit more planning on the fly, because the quantity changes according to how watery or juicy they are. Italians always use the long, roma-type tomatoes for making sauce.

The trick is in using fresh tomatoes is in the technique. You can either:

1. Puree the whole tomato, skin and all and dump it in a hot pan which already has a clove of garlic an onion (an optional pinch of hot pepper) sizzling in it. It should make alot of noise as the first bits caramelize as they hit the pan. Then, reduce to sauce consistency and mix in fresh chopped basil at the end.

2. In a hot pan with a little more oil than you are used to using (cover the whole bottom and then a little more) throw in a whole clove of garlic and the tomatoes cut in half - cut-side down. Let them caramelize a bit and then go at the whole mix with a stick blender. Reduce to sauce consistency and add the herbs of your choice.

Though, fresh tomato sauce depends on the ripest tomatoes - something you are not going to find beyond September. Italians themselves, would rather buy jarred or tetra-packed tomatoes in the Autumn and Winter than attempt to make a sauce with rock-hard, imported green tomatoes that have been gassed to look red.

I would blanch and peel them. About two pounds of tomatoes equals a big can. While not marinara, Marcella Hazan's tomato sauce with butter and onions is totally nom nom.

This is, hands down, the best fresh tomato sauce I've ever made. I make it at least once a month.

http://abcnews.go.com/Nightline/recipes-italian-favorites-scott-conant/story?id=5670217

I just made some marinara sauce this weekend, using fresh tomatoes, but it still called for tomato paste. I wonder if it's to make it thicker?

Oh yes, best EVER is from one of the Silver Palette cookbooks, maybe it was the first. Incredibly wonderful, worth the work.

@tb1010: an Italian friend of mine taught me to do just that! score the skins with a knife before blanching, then they peel off really easily!

Since I discovered roasted tomato sauce I only make that. So simple, delicious and really brings out the flavors.

My recipe is similar to this: http://thebittenword.typepad.com/thebittenword/2009/08/easy-oven-roasted-tomato-sauce.html but I use an entire bulb of garlic which I separate into cloves and then place them (unpeeled) in between the tomatoes. Remove when soft and let the tomatoes continue to roast. Add a little balsamic vinegar to the finished sauce if you like.

I take about ten large plum tomatoes, mark with an X with a knife on one end, plunge them in boiling water for 30 seconds, and then peel off the skins.

Dice three or four garlic cloves, two shallots, and a whole onion. Heat up some olive oil, then soften these ingredients in the oil till they soften and border on browning. Add herbs -- my favorite are as much thyme as I can bear pinching off the stem, some dried rosemary, and some dried oregano. (I wait to salt & pepper till the end).

Let the herbs cook a bit, getting fragrant, and a one shredded carrot, if you have it. Then add your tomatoes, trying to crust them with your hand as you go. If you don't have enough "juice" to make you comfortable, add a splash or red wine. Simmer as long as you want...for me, usually an hour and a half...and then puree as much as you want to get the texture you desire.

Add salt, pepper, and red pepper to taste.

Gracious, I need to edit before I post. Sorry. "Crush" the tomatoes. And I usually cook this all on medium, except when I want to get the whole sauce initially up to a boil before they go on Low for the long simmer.

I have had fantastic luck with this cooked sauce...
http://likemotherlikedaughters.com/2010/07/fresh-tomato-sauce-for-pasta/
It is a compilation and adaptation of several recipes. Fresh tomatoes, sweet garlic, sublime olive oil -- cooked properly it is all you need! Good luck! It is well worth searching out the perfect sauce recipe!

Makes about 1 quart of Marinara sauce

Tomatoes 2 lbs
Olive Oil 1/4 cup (most of the time I use 2 tablespoons instead)
Fresh Basil 4 leaves
Oregano (dried) 1/2 teaspoon
Garlic 2 cloves (if you can find fresh heirloom garlic it really makes a difference)
Salt 1/2 teaspoon
Pepper 1/2 teaspoon

Blanch and Peel Tomatoes and then coarsely chop.

Sauté garlic in olive oil until soft.

Add chopped tomatoes, bring to a simmer.

Add all remaining ingredients and let simmer for 10 minutes. The longer you simmer the thicker and better tasting it gets. I sometimes add 1/2 a chopped onion to this sauce. I grow my own tomatoes so I tend to use different varieties in each batch depending on what is ripe when I make it. But, if you're buying them, get Roma or San Marzano tomatoes. They have less juice and a richer flavor. Also, be sure to taste along the way. Depending on how acidic your tomatoes are, you may need to add a little sugar. Start with 1 teaspoon then add more if you need to. I use this same recipe for canning but I add 2 tablespoons of lemon juice for the canning process. Good luck!

Hi, in my blog i made marinara sauce with fresh roasted tomatoes.

It's great, here is the link: http://senioritaskitchen.blogspot.com/2010/08/pennes-con-salsa-marinara-de-tomates.html

Is in spanish but you can easily translate it with Google.

:)

I like to quarter fresh local tomatoes, toss them with a few skin-on garlic cloves, olive oil, S&P, and red pepper flakes. I roast them for close to an hour at 350. When it comes out I remove the skin from the garlic. For a chunkier sauce, I like to just mash up everything with a fork and combine it with a little tomato paste, white wine, and fresh herbs. You can also puree the sauce if you don't like the texture of the skin. Does not easily make a huge batch but good for a dinner for two. Roasting the tomatoes gives it a great flavor and you can also add other ingredients like onions or fennel.

I always peel the tomatoes and try to use ones that aren't mostly seeds. I also cook it awhile to reduce.

i made a variation of the hearty tomato sauce recipe that was posted on here a couple weeks ago with fresh roma tomatoes instead of canned and it turned out GREAT. here is my recipe: http://makingelectricity.blogspot.com/2010/09/just-in-time-for-fall-tomato-sauce.html

Here's my oven roasted marinara recipe - http://www.moderncrafter.com/2009/09/marinara-and-pickles-are-done.html. I've also started adding basil and oregano to the roasting pan. It's easy and makes the house smell great.

I love both of theses:

http://smittenkitchen.com/2010/08/fresh-tomato-sauce/

http://www.101cookbooks.com/archives/golden-tomato-sauce-recipe.html (you don't have to use yellow tomatoes)