He doesn't, he's just repeated that old chestnut that we've all disproven, and even the person most responsible for perpetuating it has admitted HE was operating under one of those "common beliefs" that we all used to believe hands down.
John Palmer has changed his tune on that subject.
As YOU know, and most of us do, fermenting the beer is just a part of what the yeast do. If you leave the beer alone, they will go back and clean up the byproducts of fermentation that often lead to off flavors. That's why many brewers skip secondary and leave our beers alone in primary for a month. It leaves plenty of time for the yeast to ferment, clean up after themselves and then fall out, leveing our beers crystal clear, with a tight yeast cake.
We have multiple threads about this all over the place, like this one
https://www.homebrewtalk.com/f39/ignore-instructions-do-not-bottle-after-5-10-days-78298/
If you leave the beer alone, they will go back and clean up the byproducts of fermentation that often lead to off flavors. That's why many brewers skip secondary and leave our beers alone in primary for a month. It leaves plenty of time for the yeast to ferment, clean up after themselves and then fall out, leveing our beers crystal clear, with a tight yeast cake.
This is the latest recommendation, it is the same one many of us have been giving for several years on here.
THIS is where the latest discussion and all your questions answered.
https://www.homebrewtalk.com/f163/secondary-not-john-palmer-jamil-zainasheff-weigh-176837/
We basically proved that old theory wrong on here 5 years ago, and now the rest fo the brewing community is catching up. Though a lot of old dogs don't tend to follow the latest news, and perpetuate the old stuff.
The autolysis from prolong yeast contact has fallen by the wayside, in fact yeast contact is now seen as a good thing.
All my beers sit a minimum of 1 month in the primary. And I recently bottled a beer that sat in primary for 5.5 months with no ill effects.....
goiked, you'll find that more and more recipes these days do not advocate moving to a secondary at all, but mention primary for a month, which is starting to reflect the shift in brewing culture that has occurred in the last 4 years, MOSTLY because of many of us on here, skipping secondary, opting for longer primaries, and writing about it. Recipes in BYO have begun stating that in their magazine. I remember the "scandal" it caused i the letters to the editor's section a month later, it was just like how it was here when we began discussing it, except a lot more civil than it was here. But after the Byo/Basic brewing experiment, they started reflecting it in their recipes.