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 journalArticle

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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