Barrel racking is a common quality assurance technique performed during aging. Most wine aged in barrel develops some amount of lees sediment. Many white wines in particular are fermented in barrel and aged on yeast lees. The potential exists for reductive aromas to develop from the lees, so many winemakers will occasionally rack the wine from barrels, clean the barrel, then return the wine for further aging. Wines that are aged sur lie style will first be stirred to agitate the lees. This allows the finer lees to remain suspended in the wine while the heavier lees is removed from the barrel during cleaning. Wines are typically racked from barrel every two to four months.