During fermentation a ‘cap’ of conglomerated solids forms on top of fermenting wine due to the upward thrust of CO2 and other gases resulting from the process. Pumping over is a means of percolating the juices at the bottom of the tank through those solids–skins, pulp, and seeds that contribute character to the final wine–gently pushing them back into the mix. Additionally, the pumpover offers a way to introduce additional oxygen into the mix, keeping the yeasts (who are responsible for performing fermentation) happy. Quite a mouthful! If you stick around to see the end of the video you may catch a glimpse of winemaker Kevin Sass, tasting the Grenache (from the same batch that is undergoing pumpover), and then (responsibly) spitting it down the drain. Enjoy!