Optimization of the Dissolved Oxygen Supply for High-Gravity Brewing
Peer Reviewed Submission
MBAA TQ vol. 36, Number 2, 1999, Pages 139-154
VIEW ARTICLE
Elizabeth J. Lodolo, E. O'Connor-Cox and B. Axcell. Peer reviewed submission- this paper was originally presented as a lecture at the MBAA 111th Anniversary Convention, Minneapolis, Minnesota, September, 1998.
Abstract
The use of high-gravity brewing necessitated the optimization of fermentations with regard to limiting yeast nutritional factors These factors were previously found to be usable nitrogen and substances synthesized in the presence of dissolved oxygen (DO). The DO optimization regime for an industrial brewer's yeast was therefore investigated and determined. It was found that, for this yeast strain cropped fresh from the brewery, the optimal wort DO concentration at the time of inoculation was 16 mg/L DO. However, the initial vitality of the yeast affected this amount. Aerobically-grown yeast had a lower zero time DO requirement than brewery-fresh yeast and artificially aged yeast demonstrated a higher requirement. This highlights an important reason to maintain plant yeast in a consistent and predictable condition. The wort carbohydrate composition also affected the amount of required oxygen with high glucose adjunct worts resulting in a higher DO requirement, particularly if the yeast was previously stressed. The optimum time to add DO was determined to be 4 hr post-inoculation. At this time, the amount of DO added could be decreased from 16 mg/L to 8 mg/L without altering the yeast's fermentative performance. Therefore, by adding the oxygen at the optimum time, the amount of oxygen necessary for an efficient fermentation can be significantly reduced. The practical application of such an oxygenation regime can be achieved in a multiple fill operation by omitting oxygenation of the first brew, pitching the first brew with the entire yeast charge, and then four hours later, adding an oxygenated (16 mg/L) second brew (of the same volume).
Keywords: yeast, dissolved oxygen, high?gravity, optimization, fermentation performance
Sintesis
EI uso de procesos para elaboraci6n de cerveza de alta gravedad requiri6 el mejoramiento de las fennentaciones con respecto a los factores nutricionales limitantes de la levadura. Estos factores, encontrados con anticipacidn, fueron niti?dgeno y substancias utilizables sintetizades en presencia de oxigeno disuelto (DO). Por tanto, se investigd y determine' cl regimen de mejoramiento del DO para la levadura de una cerveceria. Se encontre; que, para esta variedad de levadura cosechada y recogida en la cerveceria, la concentraci6n dptima de DO en mosto en el memento de inoculacion fue de 16 ing/L DO. Sin embargo, la vitalidad inicial de la levadura afecte; esta cantidad. La levadura cultivada. Aerobicamente tuvo un tiempo, de referencia para DO inferior al de la levadura cultivada en la cerveceria y la levadura affejada artificialmente obtuvo valores maCs elevados. Esto resalta un razdn importante para mantener la levadura de la planta en condiciones consistentes y predecibles. La composicidn de carbohidratos del mosto tambidn afect6 la cantidad de oxigeno requerido con mostos de alto contenido de glucosa, resultando en requisitos de DO clevados, especialmente si la levadura fue procesada con anterioridad. Se determind que el momento 6ptimo para la adicidn del DO fue 4 horas postinoculacicin. En ese momento, la cantidad de DO aifadido poria ser disminuida de 16 ing/L a 8 ing/L sin alterar las caracteristicas fermentadoras de ]a levadura. Por tanto, la cantidad de oxigeno necesaria para una fennentacion eficiente puede ser reducida de manera significativa a ffadiendo oxigeno en cl momento dptimo. La aplicacidn prdctica de dicho regimen de oxigenacidn puede ser lograda en una operacidn de llenado multiple omitiendo, la oxigenacion de la primera infusion de cerveza, aplicando toda la carga de levadura a la primera infusidn de cerveza y cuatro horas trids tarde afiadir una segunda infusi6n (16 mg/L) de cerveza oxigenada (del mismo volumen).
