9-WASHING RECOVERED YEAST WITH CHLORINE DIOXIDE

https://www.mbaa.com/districts/Ontario/Events/Documents/yeast%20washing%20with%20chlorine%20dioxide%20jan%202014%20aG_GAv3.pdf 

WASHING RECOVERED YEAST WITH CHLORINE DIOXIDE 

George Agius Andrew Gould MBAA Technical Session 2014

S.16 f: Chlorine Dioxide

Why chlorine dioxide?

Chlorine Dioxide is a strong but selective oxidizing agent 

• Chlorine dioxide is effective over a wide pH range (2-10) 

• Does not react with poly phenols (tannins), that can leave a taste in the parts per trillion 

• Does not produce halogenated methane (CHX3 ) 

Masschelein J.W. 16 W

Disadvantages of chlorine dioxide

• Cannot be shipped or stored for long periods and has to be generated on site 

• Generation requires mixing a strong acid with a solution of sodium chlorite in the right proportion and for the requisite time or some well known variation 

• Requires specialized equipment for safe generation 

• Requires careful handling as chlorine dioxide gas can escape form solution and easily exceed safety limits in the air

Will chlorine dioxide eliminate bacteria without damaging yeast?

• Not much reported in the literature 

• Paper tried using activated chlorine dioxide solution mixture at pH 3 using a nominal 50ppm chlorine dioxide Johnson D., (1998) 

• Mode of generation used did not specify time and used a weak acid with chlorite 

• Produces indeterminate solution mixture where precise concentration of chlorine dioxide is not known 

• Need to start with known concentration of chlorine dioxide for control 

The test procedure used to challenge the bacteria infecting the yeast is outlined in Figure1:

1. Lager yeast (Saccharomyces carlsbergensis) slurry sample was obtained from an actual pitching tanks in a brewery.

 2. 5.0ml of lactobacillus sp inoculum added to the yeast. 

3. A sample of the 2000ppm solution of chlorine dioxide from a Prominent Generator was measured for its chlorine dioxide content. 

4. A calculated volume of the nominal 2000ppm chlorine dioxide solution is added to 100.0 ml of the inoculated yeast to obtain a desired initial concentration e.g. 100 ppm. The concentration of the 2000ppm +/- 100ppm chlorine dioxide solution was checked using the Hach DPD method kit for chlorine dioxide #58700-51. 

5. Time is started 

6. Samples of the yeast are plated using a Mann-Rogosa-Sharpe (MRS) medium for anaerobes and incubated at 28oC. Samples of the yeast were also plated on Universal Beer Agar (UBA), and incubated at 28oC . The aerobic bacteria were counted after 3days and the anaerobic after 5 days. 

7. The viability of the yeast was determined using 0.2% Eosin Y stain [McCaig,R].

TABLE 1 – RESULTS FROM EXPERIMENT 1

Table 1 shows the results for the first experimental attempt 

• In this experiment the chlorine dioxide starting concentrations tested were 25ppm and 100ppm 

• Table 1 top window shows the initial anaerobe and aerobe bacterial concentrations and the initial yeast viability 

• The lower window shows the variation of the bacterial concentration with time after exposure to the chlorine dioxide 

• The subsequent slides provide comments on the results in Table 1

TABLE 2 – RESULTS FROM EXPERIMENT 2 

Table 2 shows the results for the second experimental attempt 

• In this experiment the chlorine dioxide starting concentrations tested were 100ppm and 250ppm 

• Table 2 top window shows the initial anaerobe and aerobe bacterial concentrations and the initial yeast viability 

• The lower window shows the variation of the bacterial concentration with time after exposure to the chlorine dioxide 

• The subsequent slides provide comments on the results in Table 2

Conclusions

• Chlorine dioxide at 100ppm appears to be specific in eliminating anaerobic and aerobic bacteria from yeast 

• The viability of the yeast does not continue to decrease with time after a small drop in the first 15 minutes. This indicates that the yeast can survive the action of chlorine dioxide 

• The process of washing recovered yeast with chlorine dioxide takes considerable less time, 15 - 30 minutes, than the classical acid wash or acid-persulfate wash at 2 or more hours 

• More work is required to determine the minimum effective concentration of chlorine dioxide between 25ppm and 100ppm 

• Based on these observations the washing of yeast with chlorine dioxide merits further investigation to work out the minimum concentration of chlorine dioxide and the details of carrying it out in a practical and safe manner

References

[1] Priest F. G. and Stewart G., Handbook of Brewing (2006) 2 nd ed., pp. 318-320. CRC Press Taylor and Francis Group 

• [2] Bah, S. and Mckeen W. E., (1965) Beer spoilage bacteria and their control with phosphoric acid – ammonium persulphate wash. Canadian Journal of Microbiology, 11(2):309-318 

• [3] Masschelein, W. J. (1979) In: Chlorine Dioxide: Chemistry and Environmental Impact of Oxychlorine Compounds pp.153-163. Ann Arbor science Publishers, Ann Arbor, MI. 

• [4] Johnson D., (1998). Coming Clean: A new method of washing yeast with chlorine dioxide, The New Brewer, Sept/Oct. 

• [5] McCaig, R. (1990), Evaluation of the fluorescent dye 1- anilino-8-naphthalene sulfonic acid for yeast viability determination. J. Am. Soc. Brew. Chem. 48 pp.22-25

• [6] Hind, H. L., (1937) Brewing Science and Practice, Volume 2, Brewing Process. 4th Ed. Chapman & Hall. London. pp. 803-4. 

• [7] Goldammer, T., (2008) The Brewer’s Handbook. Apex Publishers. pp. 82-4 

• [8] Briggs, D. E., Boulton, C. A, et al, (2004) Brewing Science and Practice, Woodhead Publishing Limited. pp. 36-7. 

• [9] Hardwick, W. A., (1995) Handbook of Brewing. Marcel Dekker Inc. pp. 193-4 

• [10] McCabe, J. T., et al. (1999) The Practical Brewer 3 rd Ed., Master Brewers of the Americas. pp. 292-3.