The phenolics are located in the skins of the grapevine berries, and these trap CO₂ rising to the top of the tank when the fermentation starts, which limits the contact between the skins and the must.In order to increase the level of contact, and thus the level of extraction, the following techniques may be used:

• Pumping over (with or without aeration)
• Cap punching; with paddles or feet (don’t fall in!)
• Racking a whole tank and then returning the must back to the cap (delestage)
• Inert gas sparging
• The use of rotary fermentors.