A secondary fermentation. A small portion of young, still actively fermenting beer and yeast is added to a tank of beer at the end of primary fermentation. Since such a small supply of wort is being introduced, the new yeast has a limited food supply. It quickly exhausts the available sugars and is then forced to scavenge among a range of secondary compounds for more food. This eliminates strong and potentially offensive odors and flavors, producing an elegant and balanced flavor, and adding smoothness and body.