When the Rombauers moved to Napa Valley they had no intention of starting a winery. They did, however, have a great appreciation for the role of wine in the fine dining experience. Koerner's great aunt Irma Rombauer was author of the internationally renowned cookbook "The Joy of Cooking." It didn't take long in their new surroundings before they became fascinated with the wine industry and in 1976 Koerner and Joan became partners in Conn Creek Winery. Koerner learned the wine business first in the cellar, working hand-in-hand with the winemaker and learning all phases of winery operations. By 1980 the Rombauers had become interested in making wine under their own label; they had it custom produced in a neighbor's winery. In 1981 they sold their interest in Conn Creek and began construction of the Rombauer Vineyards winery on the property adjacent to their home.
Since 1982 Koerner has devoted himself to making Rombauer Vineyards a successful business in which the whole family participates. His great efforts have been amply rewarded. Not only have the wines of Rombauer Vineyards been consistently recognized as some of Napa Valley’s finest, the entire Rombauer family contributes on a daily basis to the winery’s management and operations.