A "punch down" is the term we use for when we push the grape skins back down in to the juice during fermentation.
When we make white wine, we usually press the grapes as soon as we receive them and ferment the juice in tanks or barrels (unless we’re make a “skin-contact” white wine, but that’s another blog post…)
When we make red wine, on the other hand, we ferment the whole grape, juice and skins altogether (sometimes even the stems too!). Those lovely grape skins are what gives us the intense color, the tannins and some of the flavors. It’s basically a big soup of juice and grape skins in our tank or open top fermenter, which we call “must”. When the must ferments, it produces carbon dioxide gas as by-product, and that pushes the solids to the surface of the must. If we let it just hang out there, we wouldn’t get all that yummy goodness that we want in our wine, so we “punch” the grape skins down into the juice regularly. The amount of punch downs a winemaker chooses to do each day will have an impact on the tannin profile of the finished wine, so the method and the frequency of these punch downs is an important stylistic decision as a winemaker. More frequent punch downs will generally result in a more tannic wine. Less frequent (or no) punch downs will generally yield a lighter wine.
All of my red wines at Willful Wine are fermented in small, open top fermenters that hold about a ton and a half of grapes. I like smaller fermentation vessels as it allows me to be more creative with the grapes I receive. I can ferment individual clones from a vineyard source separately and do some as whole cluster fermentation and some destemmed from the same source.
With fermentation vessels like this, the usual way to do punch downs is with a punch down tool, which is basically a long pole with a disc or rectangular shape on the end which you use to push the skins down to the bottom of the fermenter. At the start, or even before fermentation starts, this is hard work. The grapes are such a solid mass you could easily lean on the tool without hardly moving it and it’s a workout to push the grapes down and pull the tool up to try and get some air in to the must to support fermentation. As fermentation progresses, the skins break down, less gas is produced, and it gets a lot easier. Lastly, you have to hope that you didn’t overfill the fermenter, because then you may get a …. muffin top.
A “muffin top” is guaranteed to wreck my day during harvest. It’s all too easy to say “sure, we can squeeze those last few pounds of grapes in’’ when they’re falling off the conveyor and in to the destemmer, but if the vessel is over full and you have a yeast that is very active, you’ll get Mt Vesuvius in the fermenter, spewing grape skins over the side of the fermenter and leaving you with a tasty mess to clean up after what was already a 12-hour day. Want to see what it looks like? Click here to see a video of our 2021 muffin top mess.