A SYSTEM OF WORT ANALYSIS

Abstract

When an abnormally high or low figure is obtained in either the primary or secondary attenuation of a beer or an abnormally fast or slow fermentation occurs, the first question to be settled, even if it is not the most likely cause, is whether the proportion of fermentable carbohydrates in the wort is abnormal; and this requires a satisfactory method of determining the attenuation limit. Such a method is also required for investigating the scientific aspects of the carbohydrate composition of worts. In the course of attenuation limit determinations on worts with high proportions of sugar incorrect results were obtained, and it became necessary to find satisfactory conditions. Those found comprised (a) continuous mechanical shaking, (b) a yeast dose approximating to 0.5 grm. per 100 ml., (c) addition of sufficient yeast nutrients to ensure an excess of assimilable nitrogen, minerals and yeast bios, (d) the use of fresh yeast, (e) a fermentation time of 40 to 60 hours, (f) a standard temperature for fermentation and for the subsequent filtration. Under these conditions the result appeared to be unaffected by the (a) exact fermentation time, (b) the gas originally present above the wort (air, nitrogen or carbon dioxide), or (c) the pH of the wort within reasonable limits. Once the nutrient solution has been prepared the determination is simple; and there is no need to distil in order to determine the real attenuation, as this can be accurately calculated from the original gravity and the apparent attenuation by means of a factor which has been determined for these conditions. Even the need to add nutrients can be avoided by using a yeast dose of 5 grms. per 100 ml. and measuring the attenuation after 18 to 20 hrs. It is desirable, however, that the yeast should first be washed in an equal volume of the same wort (a) in order to replace the liquid surrounding the cells with wort of the same composition as that to be analysed, (b) in order to prevent abnormally low and drifting end-points, which may be attributable to traces of diastase excreted by the yeast. With the precautions given the two methods agree satisfactorily. A third possibility is the use of 15 to 20 grms. of yeast of the Burton type prewashed with the wort to be used and shaken rapidly for 5 to 6 hours.