What causes tomatoes to become mealy or soft?

Mealiness, or tomatoes with softened flesh, has several possible causes.

The possible causes are:

• high Nitrogen (N)
• low Potassium (K)
• low Calcium (Ca)
• too much water
• too hot
• certain varieties

By process of elimination of unlikely causes, you can narrow it down. Tissue testing can determine if Ca or K are low or if N is too high.

The most likely causes are nitrogen being too high and potassium being too low. Nitrogen should be in the range of 4 to 5.5% in the leaf tissue. High nitrogen will also cause missed flower clusters (flower abortion), vegetative shoots at the ends of flower clusters, and a curling under or "balling up" of the tops of plants.

Low potassium during the fruit development phase is problematic. K should be 4 to 7% in the leaf tissue.

Also, overly warm conditions can cause softness, but of course, that is only a likely problem during the warm months of the year.
One other thing is to not store tomatoes in the refrigerator. Tomatoes are susceptible to chilling injury that will occur below 50 or 55 degrees F.

Refrigeration also destroys the flavor!