These happen in the early stages of a wine's life, mostly at the point of fermentation. Much of how a wine tastes is a direct result of the container it was fermented in. This is not unlike the flavours a cooking pot leaches out into the dish that is being prepared. Those who have used enamel, stainless steel, copper and cast iron pans know full well how each of these can alter the flavours of food, especially if something acidic like tomatoes is being cooked. The two 'pots' most often used in winemaking are barrels made either of stainless steel or oak.
Stainless steel is relatively neutral, but oak can produce profound flavours changes in wine.
Most wines and almost all white wines are fermented in large stainless steel tanks. Stainless Steel Fermentation Stainless steel is a relatively neutral material that actively preserves the fresh fruit flavours of a grape as it is transformed into wine. After fermentation ceases, most whites and fruity reds are kept in stainless steel tanks until bottling. An alternative method places the grape juice immediately in oak barrels to ferment, making the wine less overtly fruity and more savoury, while also imparting a pleasant roasted nuttiness. This usually changes the wine's texture, making it smoother and denser, while harmonising flavours more rapidly.