O-21
Steps towards the formulation of a model foam standard
Presenter: Waha Vundla, SABMiller, Sandton, Republic of South Africa
Co-Author: P. Torline, SABMiller, Sandton, Republic of South Africa

Foam is a key attribute of beer. The laboratory evaluation of beer foam is therefore important, and numerous routine as well as research-related foam analyses are performed across the brewing industry worldwide. Despite this, no true standard for foam measurements exists. To address this shortcoming, a model foam standard has been formulated. The model foam standard comprises defined quantities of chemically pure bovine serum albumin (BSA; 0.075%), protamine sulfate (0.006%), tetrahop (0.026%), ethanol (2%), cobalt sulfate (0.012%), glycerol (0.2%), dextrin (0.2%), poly-dextrose (0.1%), ethylenediaminetetraacetic acid (EDTA; 0.001%), carbon dioxide (0.3%) and water (97.085%). All measurements were done by weight. The concentration of the different components relative to one another was found to be important. In particular, the hop to protein ratio (~1:3) was found to be critical, as was the 1:2 metal ion to isohumulone ratio. While BSA made up the main foaming protein, the smaller protein, protamine sulfate, had an additional stabilizing effect on the foam. Ethanol was found to be essential for foam formation, with an optimum concentration of 2%. The optimum interval between carbonation and packaging under these conditions was found to be 48 hours. In addition to stabilizing the model foam standard microbiologically, Pasteurisation (20 PU) had a positive effect on the foam. The model foam had a NIBEM value of ~279 ± 2.2 seconds. Further to the NIBEM method, the rate of foam collapse as measured by a pour method was ~30 ml/min (r > 0.98), compared to ~46 ml/min (r > 0.98) for a lager beer. At 865 ml (340 ml sample), the foam head (as measured by a pour method) was slightly less than that of lager beer. Overall, the model foam was more stable than lager beer foam, although the latter had more foam. The dynamic viscosity of the foam standard was 1.25 mPa.s. It had a density of 0.998 g/ml, slightly lower than that of beer (1.004 g/ml), and a pH of 4.1. The cling was 99.5 ± 0.5, compared to 85.5 ± 4.5 for a lager beer. Although this standard has been optimized for the NIBEM method as well as an in-house pour method, it has potential for use with other foam methods. In addition to providing a potential standard for foam measurements, this model foam may be useful in studies to elucidate the mechanism of interaction between the different components of beer foam. The model foam standard is currently being tested at two breweries. The results obtained will be included in the presentation.

Waha Vundla received her Ph.D. in biochemistry from The University of Neuchatel, Switzerland, and did her post-doctoral studies at The University of Nevada, Reno, where she was an International Atomic Energy Agency (IAEA) fellow. She worked as an insect scientist at The International Centre for Insect Physiology and Ecology (ICIPE) in Nairobi-Kenya, where she gained wide experience in protein work. Waha joined The South African Breweries (now SABMiller) in September 1996 and has been a member of the research team since, applying her considerable protein background to various aspects of brewing science including flavor, premature flocculation, foam and clarity. She is currently a senior research scientist, and is an associate member of the Institute and Guild of Brewing and Distilling.