I think this would also apply to beer...
From "The Home Winemaker's Manual" by Lum Eisenman
PVPP (Polyclar AT)
PVPP is sold under the brand name Polyclar AT. It is manufactured in the form of very small,
round plastic beads. PVPP is a light weight plastic similar to nylon, and this material is completely
insoluble in water or wine. PVPP is used to remove browning or pinking pigments from white or
blush wines. It is used to remove oxidized odors and for removing small amounts of bitter phenolic
compounds. PVPP is often used to fine juice pressed from moldy grapes. Sometimes a light fining
with Polyclar can be very effective and produce almost miraculous results. At other times, this
material may not be very productive.
PVPP is an easy material to use. The powder is mixed with a small amount of water and then
added to the wine. Dose levels range from 1/4 to 2 grams per gallon. About 1 gram per gallon is
considered a typical dose. This material reacts with the wine very quickly, so it can be removed from
the wine after just a few hours. However, Polyclar does not settle out of wine very quickly, and many
winemakers prefer to filter the wine after a PVPP treatment. Sometimes small amounts of bentonite
are used as a topping material to help settle the PVPP particles quickly.