The most common causes of this deformation is poor pollination or insect damage that occurred early in the development of the fruit. If it is a pollination issue, there is very little that you can do about it. Fortunately, I would not expect it to be much of a problem in the coming years. If it is insect problems, an insecticide spray program should be started shouortly after bloom starts. Your state Extension should have information on pest control in small fruits. Check with your county Extension office.