K. A. BERG (1); (1) PQ Corporation, Conshohocken, PA, U.S.A.
Enzymes, Finishing and Stability
The colloidal stabilizing activity of silica gel at elevated temperatures has not been clearly established. One earlier report said that one silica had no temperature sensitivity, whereas another was less active at 6.3°C when compared to activity at 0°C. An unstabilized American lager was treated anaerobically with a silica hydrogel (BRITESORB A100) and a silica xerogel (BRITESORB D300) at three temperatures and at a range of doses. Treated beer was anaerobically diluted to final gravity and either measured for sensitive protein or forced (5 days at 60°C followed by 2 days at 0°C) and measured for total haze at 0°C. Dose/response data were fit by least squares method to the equation: Forced total haze, in ASBC FTU = Max_Haze – (Max_Haze – Min_Haze) × (Dose/(Dose + Half_Dose)). Higher temperature increased the activity of the hydrogel but had no effect on the xerogel. Surprisingly, higher treatment temperature greatly increased the haze of unforced beer (3-fold higher at 8°C than at 0°C). The equations allow the prediction of the forced total haze at any dose or temperature. Because all the fits show a Min_Haze of 0 ASBC FTU (i.e., at infinite dose), one can also calculate the dose needed to maintain a chosen stability at any treatment temperature. Thus, the prediction that loss of colloidal stability at higher treatment temperature can be overridden by higher dose has been verified.
Ken Berg received a B.A. degree in biology (biochemistry concentration) from Cornell University in 1976, and a Ph.D. degree in biochemistry from Brandeis University in 1981. After a post-doctoral appointment at North Carolina State University, Ken designed protein purifications for Lee Scientific in St. Louis, MO. For the last 30 years he has aided PQ Corporation by supporting its silica gel plants and their food industry customers globally. His customer-support techniques include biochemistry, microbiology, optical microscopy, powder mechanics, and the chemistry of foods and silica. Ken lives near Philadelphia, PA, with his music teacher wife Shelley.