Abstract
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.
Highlights
In a brewery, control chemical analyzes are performed immediately after sampling
The difference in the results of the determination of the original gravity and alcohol content was proved by the paired t-test
The study has shown that in some cases freezing of beer or wort samples before analysis is not suitable for sample storage
Summary
The situation requires a longer delay between sampling and analysis, especially, if it is special analysis that is not performed by the brewery laboratory and the sample must be sent for analysis elsewhere, or if it is impossible for operational reasons (personnel problems, failure of the measuring instrument) In this case, proper storage of the sample before analysis is crucial, as it must be ensured that its physicochemical properties do not change and that a value relevant to the original sample is obtained after analysis. The stability of a stored sample is related to wort or other intermediate of beer production, whose chemical composition changes rapidly, but finished beer is concerned Often it occurs that analyzes must be performed from the last opened package or from a sample of draft beer, etc. It is important to know how to handle such a sample and whether the storage conditions will not change it
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