Influence of beer and wort sample freezing on the result of analysis

Freezing is a common way of storing samples including beer samples. To verify the suitability of this procedure, the results of determination of alcohol (% v/v), original gravity, color, pH, thiobarbituric acid index, total polyphenols, saccharides, limit of attenuation, free amino nitrogen, protein nitrogen by coomassie brilliant blue, iso-α-bitter acids, diacetyl, higher alcohols, esters, fatty acids, carbonyl compounds and hop oils in beer, and protein nitrogen by coomassie brilliant blue and total polyphenols in wort were compared before and after freezing the sample. It was found that most determinations were not affected by sample freezing, but the determinations of alcohol, original gravity and total polyphenols were affected. In case these very frequent determinations would need to be performed after freezing, a new uncertainty of the method was calculated for these analyzes. From the spectrum of fifteen tested carbonyl compounds, there was a statistically significant increase in the concentration of four compounds (2-methylpropanal, 2-methylbutanal, 3-methylbutanal, phenylacetaldehyde). A significant decrease after sample freezing was observed for most of the analyzed essential oils.