A simple method to determine the water activity of ethanol-containing samples

J. E. Hallsworth*, Y. Nomura

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

44 Citations (Scopus)


The water activity (a(w)) of microbial substrates, biological samples, and foods and drinks is usually determined by direct measurement of the equilibrium relative humidity above a sample. However, these materials can contain ethanol, which disrupts the operation of humidity sensors. Previously, an indirect and problematic technique based on freezing-point depression measurements was needed to calculate the a(w) when ethanol was present. We now describe a rapid and accurate method to determine the a(w) of ethanol-containing samples at ambient temperatures. Disruption of sensor measurements was minimized by using a newly developed, alcohol-resistant humidity sensor fitted with an alcohol filter. Linear equations were derived from a(w) measurements of standard ethanol-water mixtures, and from Norrish's equation, to correct sensor measurements. To our knowledge, this is the first time that electronic sensors have been used to determine the a(w) of ethanol- containing samples.
Original languageEnglish
Pages (from-to)242-245
Number of pages4
JournalBiotechnology and Bioengineering
Issue number2
Publication statusPublished - 20 Jan 1999


  • Electronic humidity sensors
  • Ethanol
  • Freezing-point depression
  • Osmotic stress
  • Saccharomyces cerevisiae
  • Water activity measurement

ASJC Scopus subject areas

  • Biotechnology
  • Microbiology

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