TY - JOUR
T1 - Studies on the impact of mixing in brewing fermentation - Comparison of methods of effecting enhanced liquid circulation
AU - Boswell, CD
AU - Varley, J
AU - Boon, L
AU - Hewitt, Christopher
AU - Nienow, Alvin
PY - 2003/3/1
Y1 - 2003/3/1
N2 - Mixing during beer production by natural CO2 evolution has been enhanced at the bench scale by headspace gas recirculation to the base of a 3.51 cylindroconical fermenter or by mechanical agitation in a 41 fermenter. Standardized lager fermentations were used to compare the two methods at a range of mean specific energy dissipation rates (epsilon(T), W kg(-1)), including similar to5 x 10(-2) W kg(-1). The latter corresponds approximately to the maximum epsilon(T) found at the production scale (similar to400 m(3)) due to natural CO2 evolution. The work has shown that gas recirculation is a viable technique that avoids the loss of volatiles found if mixing is enhanced by sparging a separate gas such as nitrogen. For both types of mixing, it was found that ET resulted in increased yeast growth and fermentation rates and an alteration in the balance of key volatile compounds, with, in general, an enhanced formation of higher alcohols and a suppression of the formation of esters. However, with gas recirculation this enhanced performance was limited to an epsilon(T) of similar to5 x 10(-2) W kg(-1) because of the tendency for excessive foaming at higher recirculation rates, whilst values up to similar to2.5 x 10(-1) W kg(-1) proved effective under agitated conditions. On comparison, at an epsilon(T) of similar to5 x 10(-2) W kg(-1), the two modes of operation gave similar results, although gas recirculation produced a slightly increased fermentation rate. The possible reasons for this are briefly discussed. Both methods seem to have the potential for reducing fermentation time and enhancing reproducibility, especially at the small scale.
AB - Mixing during beer production by natural CO2 evolution has been enhanced at the bench scale by headspace gas recirculation to the base of a 3.51 cylindroconical fermenter or by mechanical agitation in a 41 fermenter. Standardized lager fermentations were used to compare the two methods at a range of mean specific energy dissipation rates (epsilon(T), W kg(-1)), including similar to5 x 10(-2) W kg(-1). The latter corresponds approximately to the maximum epsilon(T) found at the production scale (similar to400 m(3)) due to natural CO2 evolution. The work has shown that gas recirculation is a viable technique that avoids the loss of volatiles found if mixing is enhanced by sparging a separate gas such as nitrogen. For both types of mixing, it was found that ET resulted in increased yeast growth and fermentation rates and an alteration in the balance of key volatile compounds, with, in general, an enhanced formation of higher alcohols and a suppression of the formation of esters. However, with gas recirculation this enhanced performance was limited to an epsilon(T) of similar to5 x 10(-2) W kg(-1) because of the tendency for excessive foaming at higher recirculation rates, whilst values up to similar to2.5 x 10(-1) W kg(-1) proved effective under agitated conditions. On comparison, at an epsilon(T) of similar to5 x 10(-2) W kg(-1), the two modes of operation gave similar results, although gas recirculation produced a slightly increased fermentation rate. The possible reasons for this are briefly discussed. Both methods seem to have the potential for reducing fermentation time and enhancing reproducibility, especially at the small scale.
KW - mixing
KW - fermentation
KW - yeast
KW - agitation
KW - brewing
U2 - 10.1205/096030803765208643
DO - 10.1205/096030803765208643
M3 - Article
VL - 81
SP - 33
EP - 39
JO - Food and Bioproducts Processing
JF - Food and Bioproducts Processing
IS - C1
ER -