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ORGANOLEPTIC EVALUATION OF BEER STORED IN STAINLESS STEEL KEGS VS PLASTIC KEGS


Report from the technological backup contract between Miguel Hernández University & THIELMANN

AIM AND SCOPE

The objective of this research has been to evaluate the preservation of commercial beer in THIELMANN kegs and to compare these results with those obtained from the preservation of the same beer in plastic kegs using a system called “bag-in-ball” which consists of an alufoil bat inside a PET vessel.

For a better evaluation, this study considered the most important quality parameters demanded by the consumers, including physical, chemical and sensory analysis.

MATERIALS AND METHODS

EXPERIMENTAL SETUP

Commercial beer stored in 30 liter THIELMANN stainless steel kegs was sent to Miguel Hernandez University (UMH). Once the beer was properly distributed in both types of kegs, the starting point of the essay was the following:

18 stainless steel kegs 30 liters in volume:

  • 3 of them were used as day 0 sample in order to define the initial physical, chemical and sensory properties from the beer;
  • 3 of them were tapped with modified couplers to allow the extraction of the gas from the headspace during the first 3 months of storage for the measurement of the carbonation level;
  • 12 of them were used to test the physical, chemical and sensory properties from the beer every 1.5 months during 6 months and using 3 kegs in every test to ensure the reliability of the results.

15 plastic kegs 20 liters in volume:

  • 3 of them were tapped with modified couplers to allow the extraction of the gas from the headspace during the first 3 months of storage for the measurement of the carbonation level;
  • 12 of them were used to test the physical, chemical and sensory properties from the beer every 1.5 months during 6 months and using 3 kegs in every test to ensure the reliability of the results.

BEER PROPERTIES ANALYZED

  • Beer color in EBC units and CIELab Color.
  • Sensory determinations: Color; Foam head retention; Malt and cookie flavor; Hoppy flavor; Floral flavor; Citrus flavor; Metallic flavor; Sour flavor; Bitterness; Beer carbonation; Body; Aftertaste.

RESULTS AND DISCUSSION

It is important to highlight that the evaluation of the physical, chemical and sensory properties has to consider the initial value as a reference. The aim of kegs as packaging method is to keep the original properties and flavor of beer for a long period of time, with minimum alterations implying the decrease or increase of any parameter.

  • Beer color

Beer in stainless steel kegs kept the color values constant during the 6 months, whereas the beer stored in plastic was progressively altered during the storage period.

Given that both vessels were stored at the same conditions (dark storage at a temperature of 20±5ºC in UMH facilities), and that CO2 headspace concentration values were quite similar, it is concluded that opacity differences against light from both types of kegs have a relation with the polyphenol oxidation, which is significantly higher in plastic barrels, even both vessels have been stored avoiding direct sun or artificial light.

SENSORY DETERMINATIONS

  • Color

A noticeable increase of the darkening/browning was observed in beer stored in plastic barrels, which distantly differ from the initial beer at the early 1.5 months. These differences increased gradually during the essay and agree with the ones obtained by the spectrophotometric method.

                                  Plastic keg (left) – Stainless steel keg (right)

  • Foam head retention

Foam head of beer stored in stainless steel kegs is maintained till 4.5 month of storage, being evaluated slightly worse just at the end of the essay. However, plastic kegs showed a lower foam head retention from the 3rd month.

  • Malt and cookie flavor

Minor changes were appreciated from the 3rd month in beers stored in plastic, which could be due to the beer oxidation in this type of kegs.

  • Hoppy flavor

Higher in stainless steel kegs until the month 4.5, where both samples were similar in this flavor.

  • Floral flavor

This flavor becomes undetectable in plastic kegs, but the variations are not significant.

  • Citrus flavor

Higher and constant in stainless kegs, whereas decreasing in plastic kegs until being undetectable.

  • Metallic flavor

The beer stored in both types of kegs showed a certain metallic flavor, but it was kept almost constant only in beer stored in stainless steel kegs, whereas it decreased significantly in plastic kegs.

  • Sour flavor

Sour flavor had a constant value in stainless steel kegs during the 6 months of storage, being significantly lower in beer stored in plastic kegs from the 3rd month till the end of the essay.

  • Bitterness

Slightly higher in stainless steel kegs, which kept this flavor almost constant but with no significant variations with respect to plastic kegs.

  • Beer carbonation

Beer carbonation level showed a significantly decrease in plastic kegs, which is a characteristic directly related to a loss in quality. On the other hand, beer in stainless steel kegs decreased at month 1.5, but the following values kept constant until the end of the storage period.

  • Body

Slightly higher in stainless steel kegs, which kept this flavor almost constant. Beer in plastic kegs showed a progressive decrease until being almost undetectable, which results in a lower satisfaction level achieved by consumers.

  • Aftertaste

Highly significant differences were found in this attribute of beers stored in stainless steel kegs and plastic kegs, especially until 1.5 month. From that point the differences were not so high but beer in stainless steel was always closer to the original aftertaste level, resulting in a higher satisfaction level of the consumers.

CONCLUSIONS

  • CO2 concentration in keg headspace is not affected by the type of keg used.
  • Beer preserves it initial color for longer periods when stored in stainless steel kegs, whereas beer in plastic kegs is oxidized. This fact is supported by the chemical analytical results and also by the sensory analysis.
  • Bitterness is an attribute not affected by the type of keg used.
  • Sensory analysis shows that beer stored in stainless steel kegs preserves its initial characteristics.

As a final conclusion of the tests developed, it can be confirmed that beer storage in stainless steel kegs results in a better preservation given that the beer keeps its original physical, chemical and sensory properties for longer periods of time.

 

Special thanks to Miguel Hernández University and THIELMANN Innovation & New Products Department.

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