Summary: The paste that results from cooking tomatoes for several hours, then straining them and reducing them to a thick red, richly flavored concentrate.
Description: Tomato paste is a thick paste that is made by cooking tomatoes for several hours to reduce moisture, straining them to remove the seeds and skin, and cooking them again to reduce them to a thick, rich concentrate. In contrast, tomato purée which consists of tomatoes that have been boiled briefly and strained, is a liquid with a consistency between crushed tomatoes and tomato paste.
It was traditionally made in parts of Sicily, Southern Italy and Malta by spreading out a much reduced tomato sauce on wooden boards. The boards are set outdoors under the hot August sun to dry the paste until it is thick enough, when scraped up, to hold together in a richly colored dark ball. Today, this artisan product is harder to find than the industrial (much thinner) version.
In the UK, paste is referred to as purée or concentrate.
In the USA, tomato paste is concentrated tomato solids (no seeds or skin) and usually no added sugars or seasonings, with a standard of identity (see 21 CFR 155.191).