engleski

Evaluation of visual characteristics of beer using the computer vision method

Introduction. The aim of this study was to monitor the colour and stability of foam of different types of beer (light and dark beer) using a non-destructive method - computer vision and digital image analysis. Materials and methods. Beer colour and beer foam stability of different beer types (declared as dark and light beer type) were measured using computer vision method. Beer foam stability, expressed as change in foam height over time, is modelled using an exponential decay model. Measurement of foam decay generally involves measuring beer drainage or the decreasing height of the head. Results and discussion. The dark beer was less bitter (16.75 IBU), with higher polyphenol content (181.80 EBC), compared to the light beer style (bitterness was 26.50 IBU, total polyphenol content 103.50 EBC). Alcohol content was mostly below 5% (4.82% for the pale beer and 4.90% for the dark beer), and pH was 4.39 for the pale beer and 4.43 for the dark beer. Beer colour was expressed in the CIEL*a*b* colour system, with darker beers having lower values for lightness (L* = 28.7), higher values for a* = 10.4, and lower values for b* = 4.4. In contrast, light beers were brighter (L* = 65.5), with lower values of a* = 7.7 and higher values of b* = 4.4. Dark beers had higher EBC, lower L*, and higher a* values than pale beers due to the use of colouring malts that were kilned and roasted at a higher temperature at which Maillard reaction products were formed. The change in beer foam over time is a combination of liquid removal and bubble decay. The dark style of beer showed much more stable foam than the light beer. Beer foam height was statistically different (p< 0.05) between light and dark beer, with dark beer samples having higher initial foam height (66.1 mm) compared to light beer (48.7 mm). Dark beer samples had lower values of rate constant (0.0091 s(-1)) and higher values of foam half-life time (76.1 s), implying that dark beer had more stable foam than light beer. In contrast, light beer samples had higher values of the rate constant (0.0110 s(-1)) and lower values of the foam half- life time (63.2 s). The applied mathematical model (exponential decay model) was found to be suitable for predicting the change in foam decay rate and foam stability of light and dark beer samples. Moreover, the values of foam height of dry and wet part of foam were well predicted by the exponential decay model. Conclusions. Computer vision has been shown to be a suitable, objective, reproducible, and reliable method for measuring the colour and stability of beer foam (total foam, wet foam, and dry foam) for light and dark beer varieties.

beer ; colour ; foam ; computer vision ; modelling

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