By 1910 the state of California was producing over forty-five million gallons of wine, as well as exporting wine to Europe, and in 1918 the powerful California Wine Association, headquartered in Contra Costa County, paid its highest dividend. That would shortly change, however. National Prohibition became law on January 16, 1920, prohibiting the sale of alcohol for any but medicinal or sacramental uses. In California as a whole, the number of wineries went from approximately 700 in 1920, to 140 by the time prohibition was repealed in 1933. But in Sonoma County the number of acres in grapes went from 17,080 in 1919 to 21,496 in 1933, a 4,000-acre total gain of acreage planted in vineyard. Overproduction of grapes for juice and raisins collapsed this market as a whole in the mid-1920s, but Sonoma County was able to maintain its high percentage of wine grape vineyards. While research did not reveal specific information on the impact of Prohibition in Glen Ellen, historian Lynn Downey has written that, “In the Sonoma Valley, many businesses failed, and others barely held on. When repeal finally came in 1933, the damage could be seen all over town: closed wineries, abandoned buildings full of discarded machinery and rotting barrels, and shabby neglected vineyards.”
While the Eighteenth Amendment to the United States Constitution prohibited the "...manufacture, sale, or transportation of intoxicating liquors within, the importation thereof into, or the exportation thereof from the United States...," drinking in Sonoma County, particularly at the resorts, still went on behind closed doors. It would appear that the larger, established wineries in the Glen Ellen area were able to withstand Prohibition, whereas many of the smaller, lesser known names suffered. In the month of January 1920, the same month that Prohibition was enacted nationally, the 1920 census was taken in the Glen Ellen Township, which included west and east Glen Ellen, Glen Ellen Village, and Kenwood. The enumerator noted that the following names were still involved in the wine industry: Charles J. Pagani, viticulturist; Rose Pagani, bookkeeper at winery; Leopold Justi, winemaker; Felice Pagani (owner of the old Chauvet Winery), vineyardist and winemaker; and Louis C. Kunde, vineyardist.
In contrast, in the 1910 census of the Glen Ellen Township, the following called themselves farmers/vineyardists: Louis C. Kunde, John B. Valle, Arundel Pagani, Ramiges Abati, Christopher H. Bruning, Richard Pagani, William and Benjamin Bihler, Leopold Justi, Emile Graziani, Attilio Romani, Julius Wegener, Henry J. Chauvet, and Robert Hill.24 Whether or not the larger wineries bought out some of these smaller growers in these years, explaining the expansion of vineyards as a whole in the Sonoma County Viticultural District, would take additional research.