Barrel Fermentation

How it differs from tank fermentation

In a stainless steel tank, the fermenting must is easy to cool, easy to punch down, and easy to measure. In a barrel, the volume is small, the surface area to volume ratio is high, and the temperature is far harder to control. The trade-off is that the wine is in constant contact with the oak, leaching tannin, vanillin, lactones and other compounds, while also picking up subtle micro-oxygenation through the wood pores. A fermenting barrel will typically rise 10 to 15 degrees Celsius above ambient, which can push the fermentation into a fast, ester-rich zone or, if the cellar is hot, into stuck or volatile territory.

Why winemakers choose barrels

The reasons are sensory, not economic. Barrel fermentation adds complexity, but it also adds cost: a new French oak barrique costs roughly 800 to 1,200 pounds. Winemakers use them selectively, often for a portion of the juice, blending back the barrel-fermented lot into a larger tank of tank-fermented wine to lift the final blend. This is a standard technique in top English Chardonnays from producers such as Gusbourne, Ridgeview, Hambledon, Chapel Down and Wiston.

How it is done in UK cellars

After pressing and settling, the clarified juice is transferred into clean, sulphur-treated barrels, usually filled to within a centimetre of the bung. A cultured yeast or a pied de cuve from the previous vintage is pitched, the bung is left off or replaced with a loose stopper, and the temperature is monitored twice a day. The ferment may take two to three weeks. After pressing the wine off the gross lees, the barrels are topped, sulphured and left on fine lees for several months with regular bâtonnage, the stirring of the lees back into the wine.

For Pinot Noir, whole-bunch or whole-berry ferments may run in barrel, with the cap punched down by hand two or three times a day. This is labour-intensive but builds a silken tannin structure that is the calling card of premium English still red wines.

Choosing oak in the UK

Most English producers use French oak from forests such as Allier, Tronçais or Vosges, often a mix of new and one-year-old barrels. American oak is rarer but exists. The toast level, light to medium, is chosen to add spice and structure without overwhelming the fruit. Some producers use larger 500-litre puncheons instead of barriques, which give a gentler oak signature and are increasingly popular for Chardonnay and Pinot Noir that will spend a long time on lees.

Oak from the Limousin and Tronçais forests is also imported and coopered into barrels by firms such as Tonnellerie de l'Adour, Seguin Moreau and François Frères, all of whom supply UK cellars. The choice between tight-grain and loose-grain oak, between new and used, is one of the most important decisions a UK winemaker makes each year.

Practical considerations

Barrel fermentation is not free. A cellar needs a barrel room kept at a steady 12 to 16 degrees Celsius with humidity around 70 to 80 percent to slow evaporation, the so-called angel's share. A small English winery might run 20 to 50 barrels; a larger one several hundred. Barrels are usually replaced every three to five years for white wines and up to seven for red, then sold on to distilleries or smaller producers. The whole programme has to be planned at least a year in advance, because cooperage lead times in France are long.