Determination of volatile compounds during deterioration of African opaque beer using a stir bar sorptive extraction technique and gas chromatography-high resolution mass spectrometry.

Opaque beer traditional to African communities undergoes quick deterioration and is consumed within 7 days of its production. The current study has utilized a stir bar sorptive extraction technique followed by GC-HRT determination to trace variations of 84 volatile compounds in four opaque beers commonly brewed in South Africa over the 7-day shelf life period. The major fruity esters were observed to increase up to Day 4 and eventually decreasing until Day 7 where their levels were finally lower than Day 1. Aldehydes reduced drastically and were less than 50% on Day 2 and becoming almost undetectable at Day 7. The common beer alcohols (phenylethyl alcohol and 3-methyl-1-butanol) decreased during beer shelf life while phenolics with undesirable medicinal tastes (creosol and -cresol) increased up to 24-fold by Day 7. This study might open future research perspectives around opaque beer traditional to African rural communities.