KBX showed up in the garden of Martha Hufford about 15 years ago. She liked the flavor quite a bit and sent out seed to quite a few people including me. I’ve grown it just about every year since getting seed from Martha in spring 2008. KBX has the tangerine gene like the Kelloggs Breakfast parent. The only thing we know about the other parent is that it was potato leaf as is KBX. The advantage of KBX is that it does not get crud from growing in lower than optimum temperatures. Crud is a physiological condition that affects Kelloggs Breakfast under the right conditions. KBX also tends to produce more fruit and the fruit tend to be more uniformly large sized than KB. Both KBX and KB are nematode susceptible and septoria susceptible, but then, this is true of almost all heirloom tomatoes. Flavor of both KBX and KB tends to be exceptionally good though to my taste buds, KBX is slightly better. As noted above, both suffer in extreme heat so they have to be planted as early in the spring as possible for southern tier states.
All green when ripe tomatoes turn soft as they ripen. They go from grass green to a slightly paler and more translucent color and some of them then turn a very pale shade of yellow. Don’t rely on color to tell you when one is ripe. Use the squeeze test.
Interesting story: when my son was about 11 years old, he would NOT eat a tomato though he loved pizza and spaghetti and other foods made with tomatoes. One evening, I brought in a perfectly ripe juicy Aunt Ruby’s German Green and sliced it on a plate in the center of the table. When he got to the table, he looked and asked, “what’s that?”. I told him it was a tomato and to try a slice because it was very good. He got the tiniest slice on the plate and carefully cut off the tiniest bit to taste. Then he ate the tiny slice and reached for another slice on the plate. After that, he just grabbed the entire plate and said “MINE!”. From then on, I had to beat him off of the Aunt Ruby’s German Green plants so I could get enough seed to keep growing them.
PG, A good fertile sandy loam soil produces very good flavored tomatoes. I only know of one variety that tastes significantly different if grown in red clay soil. That variety is Piennolo which you can read about if you care to do a search. In Italy, they are grown in the volcanic soils around Mount Vesuvius to produce their unique flavor. I have one small area of red clay soil in my garden which just happened to be where I grew my first Piennolo tomatoes. The flavor was amazing, rich, intense, and just dripping with TOMATO taste. Since then, I make a point of growing Piennolo in similar soil if I possibly can. Other than this, in Israel, tomatoes have been developed with significant salt tolerance. When watered with brackish irrigation water (high salt content), these tomatoes are much sweeter.
To grow the best flavored tomatoes, focus on doing things right. Start with the right genetics. Plant in rich heavily composted soil. Fertilize appropriately. Keep the plants healthy and pest free. These are the conditions that tend to produce tomatoes with “amazing” flavor. All else being equal, the more compost a tomato plant has to grow in the more each plant will produce and the better the fruit will taste.