The dissolved oxygen contents of air-saturated worts and sucrose solutions determined with an internally calibrated polarographic oxygen electrode show a linear decrease in the gravity range 1 -016-1 -075. The level at S.G. 1 040 is 8 5 mg/litre at 20 C.Key words: oxygen, wort, analysis-method. IntroductionThe measurement of the absolute quantity of dissolved oxygen in wort is difficult because of the interference of organic materials in chemical methods*-7 and the problem of relating the activity or partial pressure to concentration when electrode methods are used.3 This exists whether or not the electrode is covered with a membrane."Published data on the oxygen levels of air-saturated worts vary considerably, depending upon the method of analysis used. For S.G. 1-040 worts at 20°C the following values have been reported: 5-6 mg/litre by polarography1 (corrected from the reported value of 51 at 25°C), 5-9 mg/litre by manometry,8 6-2 mg/litre by indigo-carmine,1 and 7-8 mg/litre by gas chromatography.1 Although the last value is probably the most accurate, in none of these sets of data was a linear decrease in solubility observed with increase in gravity, as would be expected from a comparison of the published data for the solubility of oxygen in saline solutions."The use in brewing of the Digox EC-3 oxygen analyser has recently been reported.0 In this instrument calibration is by the addition of a known concentration of oxygen, produced electrolytically in a separate cell, to the sample before it reaches the measuring cell.The Digox EC-3 analyser has been used to measure the dissolved oxygen content of a range of air-saturated sucrose solutions and worts. ExperimentalSucrose solutions in the gravity range 1016 to I 075 at 2O°C/2O°C were made up in distilled water containing potas sium chloride added at a rate of 0-5% of the sucrose con centration. These were attemperatcd to 20cC, saturated with air by blowing in air through a sintered disc for 20 min, and then passed through the Digox EC-3 oxygen analyser at a flow rate of 10 litres/hour. The measuring electrode was calibrated by the electrolytic addition of 1 00 mg/litre oxygen to each sucrose solution. Solubilities were corrected to 760 mm Hg total pressure. Results and DiscussionThe air saturation levels of oxygen in sucrose solutions at 20°C in the gravity range 1016 to 1075 arc shown in Fig. I, where it can be seen that there is a linear decrease in solu bility with gravity. A similar graph was obtained for brewery worts. The concentration of oxygen at S.G. 1040 was 8-5 mg/litre.The extrapolated value for the oxygen concentration in water (9-4 mg/litre) is higher by 0-2 mg/litre than the highest published value,8 possibly due to slight supersaturation or the samples.The effect of temperature on ihc air-saturation levels of sucrose solution S.G. 1-045 over the range I5-3O°C is shown in Fig. 2.
During prolonged storage there is a reduction in the bittering potential of commercial samples of pellets made from either powdered Northern Brewer or Styrian Golding hops. These losses are particularly pronounced for Northern Brewer pellets stored at ambient temperature in ruptured packs. Hop pellets can also lose substantial quantities of essential oil during prolonged storage at ambient temperature and usually develop marked off-aromas. Such pellets are clearly unsuitable for dry hopping beer or for late additions to the copper. Beers brewed using pellets which have been stored warm usually have shorter shelf-lives than similar beers brewed using pellets which have been stored chilled. Changes in brewing performance can be minimized by storing hop pellets in sound packs at temperatures below 12°C.Experience on the commercial scale has shown that whole hops stored at ambient temperature appear to lose up to 21% of their initial bittering value over a period of 18 months.
Humic acid, and the water-and acid-extracted residue fractions obtained from it, stimulated the development of invertase activity in beet disks during aging. Those fractions which showed most effect on invertase development also caused the greatest numbers of sporangia to be formed on several species of the Actinoplanaceae (Actinomycetales) cultured on agar with incorporated humic acid. The results are discussed in relation to an 'aromatic core' present in the humic acid.
An atomic absorption method is described for the determination of polydimethylsiloxane resi dues in beer, in the concentration range 002-0-5 mg/litre. Actual levels found were 0-02-0-15 mg/litre from fermentations treated with 2-3 mg/litre silicones.
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