Treatments with ethanol and acetaldehyde vapours were conducted by placing
the conical flasks containing the discs in 2 litre glass jars, sealing them with a
Suba-Seal and then injecting a known amount of ethanol or acetaldehyde onto a
filter paper inside the jar. The volumes of ethanol and acetaldehyde to be added
were determined experimentally to give starting concentrations of 0.1, 0.5 and 1.0%
ethanol or acetaldehyde vapour. The jars were left sealed for 4 hours and the gas
composition inside checked hourly by gas chromatography.