Definition - What does Pump-Over mean?
A pump-over has the same purpose as a punch-down. By using a pump, wine is pulled from a valve located near the base of a fermentation vat. It is then drawn through the pump into a hose whose end is located at the opening of the vat, where the fermenting juice or wine is then poured or sprayed over the cap.
WineFrog explains Pump-Over
A pump-over keeps the fermentation even and allows for a controlled oxygenation of the wine. It also allows for carbon-dioxide to escape and any other unwanted bi-products such as acetone or sulphuric odors.
By the action of the wine pouring or being sprayed over the cap, the wine also has consistent skin contact which will impart aroma, flavors and structure into the wine. Within the two to three weeks that it takes a fermentation to be completed, pump-overs are done up to four times per day.