What is An Heirloom Tomato?
By: Becky Bracken
Published: July 13, 2011

Heirloom tomatoes are most typically grown from seeds handed down through time that have not been genetically altered. The resulting fruit comes in all sorts of colors, sizes, shapes and most importantly, flavors. Although commercial farmers have taken liberties with varieties of heirloom tomatoes because of their recent comsumer popularity, there are still a few genuine heirloom tomato varieties out there. Generally, heirloom tomatoes are the result of one of the following lineages: 

Commercial Heirlooms: Open-pollinated varieties introduced before 1940, or tomato varieties more than 50 years in circulation.
Family Heirlooms: Seeds that have been passed down for several generations through a family.
Created Heirlooms: Crossing two known parents (either two heirlooms or an heirloom and a hybrid) and dehybridizing the resulting seeds for how ever many years/generations it takes to eliminate the undesirable characteristics and stabilize the desired characteristics, perhaps as many as 8 years or more.
Mystery Heirlooms: Varieties that are a product of natural cross-pollination of other heirloom varieties.

And because industrial farming is rapidly killing off entire varieties of tomatoes, it's never been more important to preserve the lush diveristy of tomatoes. You can read all about the history and legacy of heirloom tomatoes at Gary Ibsen's TomatoFest, a comprehensive site dedicated to all things tomato.