A study of Saccharomyces uvarum fermentation in a microgravity environment.

Sterrett, K.S., Luttges, M.W., Simske, S.J., Edelen, C.L. and Patino, H.

Abstract
In a normal lager fermentation, carbon dioxide bubbles rise to the top and yeast cells sink to the bottom of the fermenter, in consequence of the action of the gravitational pull of the planet. To investigate the effects of a lack of gravitational force on the process, fermentation trials were conducted during two space shuttle flights in February and March 1994, using slightly modified versions of laboratory apparatus developed for other experiments in space. Eight 1 ml hopped wort samples, pitched with lager yeast, were fermented on the first flight and four on the second. On returning from space, the yeast cell count and attenuation of each sample were determined and the yeast was tested for viability and morphologically examined. Both the yeast and the green beer were also analysed to determine their protein composition. The returned samples were propagated until sufficient yeast was available to carry out fermentation trials on the 1 litre scale. Yeast propagated from each of the spaceflight fermentation samples was used to pitch the first of a set of five fermentations, the second and subsequent fermentations being pitched with yeast cropped from the previous fermentation in the series. The first fermentation in each set showed slower yeast growth, a lower maximum cell count and a decreased cell sedimentation rate compared to control samples which had never left the ground. However, all parameters had returned to normal by the time of the fifth fermentation. Electrophoresis of returned samples revealed a significant increase in one protein band (67 kD), thought to represent a stress protein similar to those formed in response to heat shock. The altered growth and sedimentation of the returned yeast may also indicate an increase in the incidence of respiratory deficient (petite) mutation during space travel. However, the viability and cell morphology of the yeast did not appear to be affected by weightlessness.
Keywords : brewers' yeast fermentation growth performance