About 10% of my tomatoes have hard, brown patches on the surface. This is called russeting, and is caused by a number of factors. It is a well-known problem with greenhouse-grown tomatoes.
An expert has told me there are many factors that can cause russeting. I've been unable to find a list, but will update the post when more information is available.
In the meantime, know that if you have tomatoes that look like this,the problem can be identified as russeting.
