Rutherford Ranch reds see 12-16 months in a combination of American and a little French oak, while the Round Hill wines are mostly in American oak barrels for 12 months. Swain uses American oak more with Zinfandel because it brightens the fruit's raspberry character, while French oak is more compatible with cabernet sauvignon and merlot. Troncais gives the wine more backbone and a lemony component, while Nevers provides a little nuance of butter and vanilla. Sometimes I use all of them if the fruit calls for it. He maintains that after eight or nine months in oak, chardonnay tastes like the oak and is over the top, but the fruit always pops back.
Wood aging times are also subject to other factors.
Round Hill's red wine long suit is cabernet sauvignon. Swain makes merlot, but he has some firm opinions on a lot of the merlot in the market. Too many merlots are like cabernet sauvignons. There's a lot of merlot planted in the wrong areas. The mid-valley in Napa is good for merlot, because the conditions are more moderate there and merlot needs to be ripe, otherwise it will be vegetal.