Heavy pressure
I’m so pleased you’re paying such attention to detail in your winemaking. Absolutely we need to be concerned about extracting bitter seed tannins in our wines and during pressing we must certainly be vigilant. This is when the pressure of pressing can sometimes extract a number of bitter phenolics from seeds and skins; a few of these compounds can contribute extra tannin and “grip” to a wine, but too much can push a wine over a bitter and gritty cliff!
This is why, towards the end of pressing, many winemakers take a “press cut” to separate out the last 10–20% or so of the wine that comes out of the press. Often we’ll add it all back in, but it’s nice to be able to keep it separate for later evaluation. Taking press cuts allows you more control in the balance between wanting to make sure you squeeze out every last drop but also wanting to be left with the best wine possible.
You’re also on to something when you’re guessing that a typical home basket press is actually a pretty gentle way to separate the skins and seeds from your new wine. There is a reason that many uber-premium wineries, especially those that specialize in Pinot Noir, have spent many thousands of dollars for the new generation of “traditional” 3–8 ton basket presses for their fine wines. The typical commercial bladder press (which inflates a big balloon inside a big metal drum, pushing the must to one side against interior drainage channels) can reach pressures of 2 bar or more so winemakers can, as a buddy of mine says, “squeeze the snot out of the grapes,” not that you would want to. While there’s no way that a typical home basket press can reach those kinds of pressures, I still do recommend winemakers keep a sharp eye (and sharp tastebuds) on the wine (or juice) that comes out toward the end of pressing. Even if no seeds are broken (they’re pretty strong little nuggets and rarely “rupture” even in commercial-sized presses), a good hard last squeezing on the ol’ basket press can still cause some bitter and phenolic liquid to come out.
