High gravity brewing- study of the affect of ethanol tolerance and nitrogen supplementation
Special Symposium - Innovations in Food Technology (LMC Congress)
White BioTech & Related Processes (Food-2a)
Keywords: Brewer´s yeast, high gravity brewing, ethanol tolerance, nitrogen limitation
High gravity brewing is currently one of the most popular brewing techniques. Whereas normal gravity beer fermentation is performed in the range of 12-15ºPlato, high-gravity fermentation involves production of beer wort of up to 18ºPlato and even higher. In the process of high gravity beer fermentation, the yeast is exposed to a number of stressful conditions: high osmotic pressure, high specific gravity, low temperature and high ethanol concentrations at the end of the fermentations. In this study, we investigated the two major limiting factors of the yeast performance in high gravity brewing- ethanol toxicity and limited nitrogen availability.
We characterised, in series of batch cultivations, at average gravity of 14°Plato as well as at high gravity- 21°Plato, two yeast lager beer strains: the ethanol tolerant AJL 3126, and the less ethanol tolerant strain AJL 2252. The wort at 21o Plato was prepared with the addition of highly fermentable maltose and glucose syrups to the wort with average gravity. The physiological characterisation included growth characterisation as well as characterisation of the carbohydrate and individual amino acids profiles by HPLC. When comparing the two strains, both for normal and high gravity fermentations, AJL3126 showed higher specific growth rates and a higher final ethanol concentration. The ethanol concentration was up to 54 g/L, for the fermentations at 14° Plato and up to 86 g/L for the fermentations at 21o Plato. For both strains maximum cell concentrations were observed after 120 hours for the fermentations at 14°Plato and after 150 hours for the fermentations at 21o Plato. The ethanol production started in the first 40 to 50 hours of the fermentations. For the fermentations at 21° Plato, the fermentations ended with some residual amounts of maltose and maltotriose. From all fermentations, samples from early exponential and stationary phases were collected for extensive intra- and extracellular metabolome analysis.
For the effect on addition of different nitrogen sources, we examined the effect on the addition of urea, ammonium sulphate and enzymatically generated nitrogen sources on the fermentation performance at 21°Plato of the popular lager beer yeast strain Weihenstephan 34/70. In all cases of nitrogen supplemented fermentations, the yeast strain showed similar specific growth rate and ethanol productivity compared to the control non-supplemented fermentations, but showed significantly higher fermentable sugar utilisation. In addition, nitrogen supplemented fermentations showed improved flavour and aroma profiles of the final beer, as for example in terms of reduced amounts of acetaldehyde, ethyl acetate and isoamyl acetate.
Presented Wednesday 19, 15:20 to 15:35, in session White BioTech & Related Processes (Food-2a).
