What is a cap? What is “punching down”? Why is it important to punch down?
If you’ve ever attempted to make a big red wine at home from fresh grapes - but the finished product lacked color, taste, or tannin structure - chances are, your wine could have benefited from a winemaking technique known as “punching down”. If you make wines from kits, you will certainly benefit from this knowledge, but you won’t have to “punch down” since most kits do not include grape solids like skins, stems, and seeds.
The “cap” is the solid mass of grape skins, stems, and pips (seeds) that floats to the top of the fermenting vessel during fermentation. “Punching down” simply describes the process of breaking up the cap and pushing it back down into the wine so that the cap stays moist during fermentation. There are lots of benefits to punching down. The main reason, is that your wine will have a richer color, flavor, and tannin structure. During the early stages of fermentation, the physical act of punching down helps introduce oxygen to your yeast cells, helping them “kick start” fermentation.
Punching down also helps mix the yeast into the must. It helps keep harmful bacteria or mold from forming that could ruin your wine. It ensures color, flavor, tannins and other phenolic compounds are added to your wine. Punching down also helps dissipate heat that naturally occurs during fermentation. Left alone, the cap can reach high temperatures, providing an environment that could grow harmful bacteria.
How to punch down
First of all, take into consideration the size of your fermentation vessel. If you are making 6 gallons of wine in a 6.5 gallon fermentation bucket, you would lose a lot of wine over the side of the bucket when you start punching down the cap. You will displace the wine as you push the cap beneath the surface of the wine. Be sure to allow for this displacement when you start your next batch of wine by getting the right size bucket for your batch. Midwest always suggests using the 7.9 gallon plastic fermenter (#7135) when making the standard six gallon batches of wine.
The best tool for the home winemaker for punching down is probably a stainless steel potato masher. They’re inexpensive, easy to find, easy to clean, and have the right size footprint for punching on a small scale. Midwest advises against using any wooden device for punching down as wood can harbor bacteria that would be harmful to your wine.
When you punch down, your goal should be to gently break up the cap and work out all the lumps. When finished, the surface of the wine should be smooth and moist throughout.
You should start punching down as soon as you pitch your yeast. As already noted above, this will help mix the yeast into your wine as well. After the initial punching down, fermentation will probably proceed rapidly. Due to the buoyancy provided by the CO2 bubbles during fermentation, the cap will start to form and float to the top.
You’ll need to punch down the cap about three times per day to ensure the cap stays moist. Do not allow the cap to cake up or get dry on top.
The ideal temperature for this process is around 60 to 65 degrees Fahrenheit. Do not allow your wine to get any hotter than 70 degrees if you can help it.
At some point - and this depends on a lot of variables, like the variety of grapes, temperature, Brix, SO2 and pH levels, type of yeast used, etc. - the cap will stop forming at the top. You’ll notice that the solids in the wine will start to SINK instead of float. This happens because fermentation is slowing down and there are less CO2 bubbles to push the solids to the top.