What marketing strategies would you recommend to Mr. Behrens for retaining old customers?

One of the authors (FRK) had the pleasure of meeting Les Behrens, the owner of Behrens and Hitchcock, in 2008. Previously, Les Behrens had owned a restaurant, and Bob Hitchcock was an accountant.
Both gave up these relatively secure jobs to make wine on top of Spring Mountain in Napa Valley. Many of their wines received high ratings from Robert Parker, the most influential wine critic of all time (he has been nicknamed the Emperor of Wine), and the label very quickly became a success.
Hitchcock retired and left the partnership in 2005, and Behrens changed the name of the label to Erna Schein, after his mother. According to Parker, Erna Schein wines are “fun-filled, fruit-driven, amazingly delicious wines.” Annual, production is around 3,000 cases, which is quite small.