The 20th century saw many advances in winemaking technology and practices—particularly the introduction of temperature-controlled fermentation and controlled inducing of malolactic fermentation. One winemaking issue that is still contested in the region is the use of oak. Historically Chablis was aged in old wooden "feuillette" barrels that were essentially neutral: they did not impart the characteristic oak flavors (vanilla, cinnamon, toast, coconut, etc.) that are today associated with ageing a wine in barrels. Hygiene was difficult to control with these older barrels, and they could develop faults in the wine, including discoloration. These old barrels fell out of favor, replaced by stainless steel fermentation tanks which also controlled temperatures.