Bottle conditioning with high kraeusen wort.

Pengelly, W.L.

Abstract
A method for producing bottle conditioned beer is described in which the green beer is stored for a week at 1.5 degrees C after completing primary fermentation, filtered to remove residual yeast and suspended particles, and bottled with the addition of "high kraeusen" fermenting wort, collected between 24 and 36 hours after the onset of primary fermentation, in which the yeast is vigorously active and has consumed all the oxygen in the wort but well under half of its fermentable sugar content. The bottled beer is then stored for ten days at room temperature, during which secondary fermentation takes place, bringing about flavour maturation, while the yeast takes up some of the oxygen dissolved in the beer (thus reducing or delaying the oxidation of beer constituents which leads to off flavours) and generates the carbon dioxide required to achieve the carbonation level specified for the beer brand in question. Theoretical considerations relating to bottle conditioning, such as the equations for calculating the priming wort dosage on the basis of the brand's carbonation specification and the quantity of unfermented fermentable sugars remaining in the wort at the time of its addition to the beer (and in the beer itself if it is less than fully attenuated), are discussed together with the importance of ensuring that the yeast used for secondary pitching (whether added in partially fermented priming wort or separately) is in peak physiological condition, the problem of maintaining a consistent secondary pitching rate when using fermenting wort as the medium of yeast addition, the need to use a priming wort of the same brand as the beer to which it is added in order to avoid unacceptable variations in colour and flavour (which means that bottling can only take place when a subsequent batch of the same brand has reached the correct stage of primary fermentation, requiring the careful planning of production schedules), the blending of the priming wort into the beer before bottling, the bottle filling process and the development of carbonation during maturation.
Keywords : beer bottling maturation pitching priming secondary fermentation wort