||The examples and perspective in this article may not represent a worldwide view of the subject. (March 2010)
A plum tomato, also known as a processing tomato or paste tomato, is a type of tomato bred for sauce and packing purposes. They are generally oval or cylindrical in shape, with significantly fewer locules (seed compartments) than standard round tomatoes (usually only two) and a generally higher solid content, making them more suitable for processing. Plum tomatoes are also sometimes favored by cooks for use during the tomato off-season, as they are generally considered more amenable to handling and are therefore available in a state closer to ripe than other supermarket tomatoes.
Varieties commonly available in markets include Roma VF and San Marzano (semi-determinate; a signature tomato of Italian cuisine), though there are many other varieties, such as the short-season Ropreco Paste and the larger Amish Paste and Big Mama. Five hybrid cultivars grown in California constitute over 60% of total production of processing tomatoes. Small plum tomatoes (similar in size to cherry tomatoes) are known as grape tomatoes.
Hartz, T. et al. Processing Tomato Production in California. UC Vegetable Research and Information Center.