Pvpp is short for polyvinylpolypyrrolidone which is a polymerized and water/beer insoluble version of the soluble compound PVP (polyvinylpyrrolidone), a nylon-type polymer that has an even higher affinity for chemical bonding with polyphenols than the proteins present in beer have. This gives PVPP excellent properties as a chemical stabilizer for beer. If finely granulated, high surface area PVPP is dispersed in beer, a very high proportion of the dissolved polyphenols in the beer will bind to the PVPP particles, subsequently to be filtered out. Brewers wish to remove these polyphenols because they will otherwise with time react with beer proteins, forming insoluble complexes that will make the beer hazy. This type of stabilizer is referred to as an adsorbent.
Practical beer stabilization with PVPP can be done two different ways. The simple way is single use PVPP stabilization, where a PVPP product with very low particle size is added to unfiltered beer, which, after a few hours of reaction time, is then kieselguhr (diatomaceous earth) filtered. The PVPP used and the polyphenols removed by it will, being insoluble, form part of the filter cake which is treated as waste. The more advanced method is using “regenerable PVPP.” This involves an extra, specific PVPP filter placed after the kieselguhr (or other filter type), where filtered beer is dosed with a high concentration of slightly coarser PVPP particles. These react—en route to the PVPP filter or via a holding pipe/vessel—with the polyphenols in the beer, and finally the combined PVPP-polyphenol particles are filtered out in the extra filter. The advantage of this technique is that the filter cake from the PVPP filter can be washed with hot caustic, dissolving out most of the polyphenols, leaving PVPP particles behind that can then be recycled in the stabilization process. PVPP is expensive, so this re-use can be desirable, especially in large breweries, Some brewers use PVPP in the form of specially impregnated filter sheets that are used after the main beer clarification stage. Regardless, PVPP is not considered an additive, as it is always filtered out and therefore is not contained in the finished beer.