Here's a little clip from Today's Wine World on whole cluster pressing:
"Since white varieties are the main thing being harvested at this early point in the annual crush, it’s a good time to talk about whole-cluster pressing. You’ll see references to it in the wine maker notes for high-end white wines.
In white wine production, to keep the flavors delicate and free of astringency only the juice is fermented. So, standard procedure is to run the freshly-picked clusters through a machine that quickly pulls off the stems and breaks the grape skins open – a stemmer-crusher.
Then the crushed grapes are sent to the press, which is like a giant strainer. A whole lot of juice runs off into a drip pan on its own. When the flow begins to let up, pressure is applied to increase the yield. And, away the juice goes to a tank or barrel to be fermented.
But, high-quality whites often forgo the stemmer-crusher to be pressed immediately. I know it sounds like you save time, by skipping a step, but it actually slows the whole thing down significantly a bit. From a cellar worker’s perspective, it’s a pain.
The thing is that using the stemmer-crusher is a very quick process that removes a whole lot of bulk.
The press, on the other hand is slow. Slow pressing is the only way to get the job done gently, so the press cycle can take hours.
If the grape are de-stemmed, you can put more of them into the press at once. It’s efficient. But, the clusters that go through the stemmer-crusher before being pressed are more likely to be damaged and to show stemmy character.
Whole cluster pressing has been shown to press out juice that’s less bitter and astringent. There’s less risk of oxidation (most winemakers use an enclosed tank-style press for their whites) and also greater clarity, which may mean less processing down the road.
This is better. It may be a pain in the neck and stretch out the work day of an already tired winemaker or cellar worker, but it’s starting things out right. So, that’s why wineries like to brag about it on their winemaker notes and when you see that it tells you something about the producer’s overall commitment to quality. Cheers! "
We plan to crush/destem our small lot of Chard before pressing, but do plan on a gentle pressing vs trying to extract every drop of juice. We understand the last squeeze will impart an unfavorable astringent taste.
I just tried to whole cluster press and it didn't go so well with my small basket press. I ended up crusing and destemming, and then pressing. All in all I didn't get as much out as I would have liked. I have heard that in the past about the last squeeze imparting astringency but my new understanding is that you really can't crack the seeds without a much larger and stronger press. My guess is it would have to be a very strong winery press. So get as much juice out as you can.