Since the early sixties he has devoted himself to the study of beer phenolics. During this period of research he has published many original papers on the kinetics of haze formation and the constituents of beer related to the colloidal stability.

Several colorimetric, chromatographic, and nephelometric tests were compared as tools for monitoring the rapid (<3 days) colloidal stabilization of lager beers by a combination of cold filtration at -1°C and treatments with polyvinylpolypyrrolidone (PVPP). No significant changes in composition were detected during storage of beer for seven days at -1°C prior to filtration on a bench scale.

The effects of dosage on a pilot-scale with different amounts of recoverable PVPP (10-50 g/hl) or single-use PVPP (10-20 g/hl) on total polyphenols, total flavanols, simple flavanoids, protein sensitivity, alcohol-cooling haze, and tannoids were compared with concomitant changes in colloidal stability, as revealed by accelerated aging at both 37 and 60°C. Close correlations were found between the results of the haze forcing tests and all tests other than the tannoid measurement made on freshly bottled beers.

Although decreases in the contents of the simple flavanoids related most closely to improvements in colloidal stability, the alcohol-cooling test was also a useful indicator of stabilization effectiveness. The colloidal stabilities of beers aged at 37°C were related to both the amounts of simple flavanoids that were oxidized during aging and also to the contents of tannoids in the aged beers.

Treatment with recoverable PVPP at the highest rate effectively stabilized the sample beer by adsorbing both the simple flavanoid precursors of chill haze and the tannoid components of protein-polyphenol complexes.

Keywords: Alcohol-cooling haze, Haze stabilization, Polyphenols, Polyvinylpolypyrrolidone, Simple flavanoids, Tannoids.

Varias pruebas colorimétricas, cromatográficas y nefelométricas fueron comparadas como herramientas para monitorear la rápida (<3 dias) estabilización coloidal de cervezas lager con una combinación de filtración en frio a -1°C y tratamientos con polivinilpolipirrolidona (PVPP). No fueron detectados cambios significativos en la composición durante el almacenamiento de cerveza por 7 días a -1°C previo a filtración a escala de laboratorio.

Los efectos de dosificar a escala piloto con diferentes cantidades de PVPP recuperable (10-50 g/hl) o PVPP no recuperado (10-20 g/hl) sobre polifenoles totales, flavanoles totales, flavanoides simples, sensibilidad protéica, turbiedad por alcohol en frio y tanoides, fueron comparados con cambios asociados en estabilidad coloidal, como se revela por envejecimiento acelerado a ambas temperaturas de 37°C y 60°C. Fueron encontradas correlaciones muy cercanas entre los resultados de las pruebas de turbiedad forzada y todas las pruebas excepto las mediciones de tanoide hechas en cervezas recien envasadas.

Aunque el decremento en los contenidos de los flavanoides simples se relaciona mas estrechamente a mejorias en la estabilidad coloidal, la prueba de alcohol en frio fue tambien un indicador util de la efectividad de la estabilización. Las estabilidades coloidales de cervezas envejecidas a 37°C fueron relacionadas tanto a la cantidad de flavanoides simples que fueron oxidados durante el envejecimiento como a los contenidos de tanoides en cervezas envejecidas.

Tratamiento con PVPP recuperable a la dosis mas alta estabilizo efectivamente la muestra de cerveza al adsorber los flavanoides simples precursores de turbiedad en frio, y los componentes tanoides de los complejos protéina-polifenol.