Time & Temperature are the Enemies of Fresh Tomato Flavor!
Tomato flavor is most greatly affected by heat, whether in processing or in the kitchen. (For more information, see "How Time and Temperature affect Tomato Flavor" below.)
How much tomato-based sauces should be heated depends on the flavor profile you wish to achieve. Some family recipes call for prolonged low-flame sauce simmering with the specific objective of creating a noticeable "cooked tomato flavor", and if that is your desired outcome, by all means, continue doing so!
But if you want to enhance the fresh tomato flavor of your sauce, here are three ways to reduce cooking time and temperature:
1) Look for "Packed From Fresh Tomatoes, Not From Concentrate" on the label.
Avoid tomato products Re-Manufactured from concentrate because they are overexposed to flavor-damaging heat. Instead, look for tomato products which say “Packed From Fresh Tomatoes, Not From Concentrate” on the label. In the US., it is illegal to print "Not From Concentrate" on tomato product labels unless it is true!
2) Buy tomato products with your desired "ready-to-use" thickness.
Because tomato processors thicken tomato sauce through "low temperature" (130°-140°F) vacuum evaporation vs. "high temperature" (212°F) stove-top cooking, your finished sauce will have more fresh tomato flavor if you avoid "cooking down" to reach your desired thickness.
Similarly, "thinning down" more highly concentrated (i.e., thicker = heated longer) tomato products like a 26% Brix tomato paste by adding lots of water also results in less "fresh tomato" flavor than utilizing a fresh-packed 12%-17% Brix tomato product which wasn’t heat-processed nearly as long.
3) Minimize "stove-top cooking" of tomato components.
To preserve maximum fresh tomato flavor, add tomato products to your sauce last! It's best to thoroughly sauté your added ingredients/spices in oil on the stove-top before adding your tomatoes and bringing the complete sauce to a brief simmer. (Sautéing also sterilizes added ingredients/spices so that finished sauce "batches" can be held under refrigeration for later use.)
How Time & Temperature affect tomato flavor.
First, while a tomato (or its pulp) is exposed to heat, it gradually releases its "fresh" flavor volatiles into the air, like the tomato aroma that fills a kitchen from a simmering sauce pot. These "volatiles" are the natural compounds that give the tomato its distinctive flavor. Once they are "cooked off," they are no longer in the sauce for your customer to enjoy.
Second, prolonged heating causes the formation of "cooked" flavor compounds as the tomato's natural sugars and other flavors "caramelize." In excessive quantity, these "cooked" compounds result in "burned" and/or "bitter" flavor. Similar heat-induced reactions also cause tomato color to progress from bright red to brownish red. That's why bright red color is a solid indication of a well-prepared fresh-tasting, flavorful sauce.
Between the two kinds of heat exposure, time and temperature, temperature is the most damaging. Therefore, a key goal to maximizing fresh flavor for both processors and cooks alike is to minimize heat intensity (cooking temperature).