I see some references say to punch down the cap twice per day, some three or four, some variable throughout the primary fermentation.
Is there a limit to how often I should punch down? Something negative that bounds how often to punch? What if a machine theoretically continuously punched down the cap?
I made wine professionally for 15 years so I have punched down a lot of caps. It kind of depends on what style you are going after and what type of grape you are working with. I started off punching down 4 times a day on my red wines and later cut it back to 2 times a day after two well known wine makers told me 4 was too many. It is a lot of strenuous work punching down by hand.
It also depends on the size of your fermentation. I was working in 1 ton tanks of grapes. As the volumes increase, it gets harder and harder to do punchdowns. Large wineries do pump overs and/or submerge the whole cap in the fermenting wine.
Here is a summary of why you want to punch down:
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 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 helps dissipate heat that naturally occurs during fermentation.
Left alone, the cap can reach high temperatures, providing an environment that helps grow harmful bacteria
I have seen twice a day in books as well, since it does take a few hours for a cap to form. There is not limit to the number of times, but the more often you do it the more tannins and flavour it will extract (or it will happen faster at least).
I also have seen a different technique to achieve the same purpose, which consists in using a pump, to pump the liquid from the bottom over the cap. Recirculating the liquid over the cap does a similar job.
At some point, you need to decide if doing extra work is worthwhile, I believe 2-3 times a day for a few days is enough.
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