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1.
J Sci Food Agric ; 99(4): 1772-1779, 2019 Mar 15.
Article in English | MEDLINE | ID: mdl-30226273

ABSTRACT

BACKGROUND: Although fatty acids have a beneficial effect on yeast growth during fermentation, their effect on foam and sensory stability of beer is negative. In general, long-chain fatty acids originate from raw materials, whereas short-chain acids are produced by yeast during fermentation. If the concentration of short-chain fatty acids, especially isovaleric and butyric acid, overreaches a sensory threshold, then an unpleasant aroma, such as cheesy or sweaty feet, can be formed in beer. RESULTS: The distribution of fatty acids, from the preparation of sweet wort to the final beer, was studied using chemometric evaluation. Differences were observed between the decoction and infusion system using four barley varieties. Attention was paid to the behavior of short-chain fatty acids, namely isovaleric acid. The concentration of isovaleric acid in commercial beers brewed in infusion and decoction systems was approximately 1.4 and 1.0 mg L-1 , respectively. The same trend was observed in experimental samples (1.3 and 0.5 mg L-1 , respectively). This phenomenon was confirmed experimentally; based on the results, this possibly explains why, during the fermentation, isovaleric acid is coupled with the redox state of yeast cell, which is given by the wort composition (i.e. by the mashing process). CONCLUSION: The formation of isovaleric acid is not only caused by microbiology infection or by oxidized hops, but also is influenced by the mashing process. © 2018 Society of Chemical Industry.


Subject(s)
Beer/analysis , Fatty Acids/chemistry , Hordeum/chemistry , Fatty Acids/metabolism , Fermentation , Food Handling , Hordeum/metabolism , Humans , Humulus/chemistry , Humulus/metabolism , Oxidation-Reduction , Saccharomyces cerevisiae/metabolism , Taste
2.
J Agric Food Chem ; 65(16): 3341-3350, 2017 Apr 26.
Article in English | MEDLINE | ID: mdl-28260371

ABSTRACT

Three bottles of different beers were found in 2015 during a reconstruction of the brewery of the Raven Trading s.r.o. company in Záhlinice, Czech Republic. Thanks to good storage conditions, it was possible to analyze their original characteristics. All three bottles contained most probably lager type beer. One beer had sulfuric and fecal off-flavors; it was bright with the original extract of 10.3° Plato. The second beer, with an original extract of 7.6° Plato, was dark and very acidic, resembling Lambic. DNA analysis proved the presence of Dekkera bruxellensis, which corresponded to its chemical profile (total acidity, FAN, ethyl acetate, total esters). The third beer contained traces of carbon dioxide bubbles, was light brown and slightly bitter, with an original extract 10.4° Plato. Because it obviously underwent a natural aging process, sweetness, honey, and fruity off-flavors were detected and transformation products of iso-α-acids were found.


Subject(s)
Beer/analysis , Acids/analysis , Beer/microbiology , Czech Republic , Dekkera/genetics , Dekkera/isolation & purification , Dekkera/metabolism , Fatty Acids/analysis , Fermentation , Flavoring Agents/analysis , Food Handling , Humans , Time Factors
3.
J Agric Food Chem ; 61(51): 12670-5, 2013 Dec 26.
Article in English | MEDLINE | ID: mdl-24308508

ABSTRACT

The rate of beer aging is affected by storage conditions including largely time and temperature. Although bottled beer is commonly stored for up to 1 year, sensorial damage of it is quite frequent. Therefore, a method for retrospective determination of temperature of stored beer was developed. The method is based on the determination of selected carbonyl compounds called as "aging indicators", which are formed during beer aging. The aging indicators were determined using GC-MS after precolumn derivatization with O-(2,3,4,5,6-pentaflourobenzyl)hydroxylamine hydrochloride, and their profile was correlated with the development of old flavor evolving under defined conditions (temperature, time) using both a mathematical and statistical apparatus. Three approaches, including calculation from regression graph, multiple linear regression, and neural networks, were employed. The ultimate uncertainty of the method ranged from 3.0 to 11.0 °C depending on the approach used. Furthermore, the assay was extended to include prediction of beer tendency to sensory aging from freshly bottled beer.


Subject(s)
Beer/analysis , Flavoring Agents/analysis , Gas Chromatography-Mass Spectrometry/methods , Taste , Food Storage , Humans , Temperature , Time Factors
4.
J Agric Food Chem ; 57(23): 11081-5, 2009 Dec 09.
Article in English | MEDLINE | ID: mdl-19904941

ABSTRACT

Solid-phase extraction (SPE), solid-phase microextraction (SPME) using carbowax/divinylbenzen fiber, and stir bar sorptive extraction (SBSE) followed by solvent back extraction have been used for the extraction of free fatty acids (caproic, caprylic, pelargonic, capric, lauric, myristic, palmitic, stearic, oleic, linoleic, and linolenic acids) from beer. Subsequent gas chromatographic analyses with flame ionization detection were used for the determination of these compounds. Medium-chain fatty acids (caproic-lauric acid) were determined as free acids, and long-chain fatty acids (myristic-linolenic acids) were determined as methyl esters after methylation by BF(3)-methanol 14%. Linearity, recovery, and repeatability of all methods have been determined and compared with the SPE method used as a reference (SPME method was used only for medium-chain fatty acid determination). All three procedures provide similar working parameters characterized by high repeatability (2.3-16.3%) and good linearity (correlation coefficient ranging from 0.9919 to 0.9999). Results of beer analyses obtained by using these three methods were highly correlated. Although all methods provide compatible alternatives, for medium-chain fatty acid analysis SPME may be a more appropriate technique due to its operational simplicity, repeatability, and low cost.


Subject(s)
Beer/analysis , Fatty Acids/analysis , Solid Phase Extraction/methods , Chromatography, Gas , Solid Phase Extraction/instrumentation , Solid Phase Microextraction/instrumentation , Solid Phase Microextraction/methods
5.
J Chromatogr A ; 1196-1197: 96-9, 2008 Jul 04.
Article in English | MEDLINE | ID: mdl-18508065

ABSTRACT

Free medium-chain fatty acids in beer originate from raw materials, mainly from the fermentation activity of yeasts, and can influence beer taste, vitality of yeasts and also the foam stability of beer. This study presents the development of the method for the determination of free fatty medium-chain acids including caproic acid, caprylic acid, capric acid and lauric acid in beer or wort using stir bar sorptive extraction (SBSE). The combination of this extraction technique with solvent back extraction of the extracted analytes and subsequent gas chromatographic analysis with flame ionization detection was used for the determination of these compounds. The influences of different solvent back solutions, sampling time, solvent back extraction times and different contents of ethanol were studied. The method had high repeatability (RSD <6.7%), good linearity (the correlation coefficients were higher than 0.9963 for quadratic curves over the concentration range 0.5-8.0mg/l) and recoveries 57-89%.


Subject(s)
Beer/analysis , Chemical Fractionation/methods , Fatty Acids/analysis , Caproates/analysis , Caprylates/analysis , Chromatography, Gas , Decanoic Acids/analysis , Fatty Acids/chemistry , Lauric Acids/analysis , Reproducibility of Results , Solvents/chemistry
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