The chemistry of beer flavor instability remains shrouded in mystery, despite decades of extensive research. It is, however, certain that aldehydes play a crucial role because their concentration increase coincides with the appearance and intensity of "aged flavors". Several pathways give rise to a variety of key flavor-active aldehydes during beer production, but it remains unclear as to what extent they develop after bottling. There are indications that aldehydes, formed during beer production, are bound to other compounds, obscuring them from instrumental and sensory detection. Because freshly bottled beer is not in chemical equilibrium, these bound aldehydes might be released over time, causing stale flavor. This review discusses beer aging and the role of aldehydes, focusing on both sensory and chemical aspects. Several aldehyde formation pathways are taken into account, as well as aldehyde binding in and release from imine and bisulfite adducts.
Teat morphology is an important parameter in choosing the most appropriate teatcup liner for a herd since the interaction between teat and liner can strongly affect the milking characteristics and udder health. Nevertheless, information on teat morphology is very scarce and rarely sufficient for liner selection. Gathering information on large scale with current techniques is time consuming, subjective and not always accurate. However, the ability to measure teat parameters in an easy way and on large scale has many applications. This study presents a new vision based measuring technique for teat shape parameters. A camera is used to obtain a 2D image of the teat and image processing analyses to determine teat length and diameters. In addition, shape parameters of teat and teat end can be defined. The resolution in length and diameters is better than 0.5 mm. The error on the length of the teats that make an angle in the longitudinal plane of maximum 25° towards the camera, is no more than 5 %. To validate the repeatability of the measuring method, the teats of one Holstein cow were measured 5 times by 8 different members of a test panel of which 5 people were experienced in working with cows. Reproducibility was tested by measuring the teats of 7 Holstein cows by the same test panel. The teats of each cow were measured once in a defined order. The sequence in which the members measured the teats was randomized. No significant differences were found between the 5 successive measurements of one person on 3 teats. Significant differences in left-front teat measurements (p=0.002) were due to the lack of cow experience (p=0.022). Teat length measurements did not significantly differ between members of the test panel as long as teats could be easily reached. However, no significant differences were found for all teats between operators familiar with cows. In conclusion, a new accurate, repeatable and reproducible method was developed to measure teat parameters in all kinds of milking parlours. To obtain repeatable and reproducible results, some training in working in close interaction with cows is advised.
As a continuation of our previous work, which concerned the binding of aldehydes to bisulfite and cysteine, this article presents more results on the applicability of 4-vinylpyridine addition to beer prior to analysis aiming at release of aldehydes from these preformed bound states, thus making them quantifiable with the headspace solid-phase microextraction method combined with gas chromatography-mass spectrometry. This article also presents the first results on spiking beer samples with cysteine prior to forced-aging, pointing to the important role of cysteine in beer flavor stability. Both the levels in free and bound aldehydes show a relatively large degree of variation among different beers, but also between marker aldehydes. For some aldehydes (e.g., hexanal), the bound amount was shown to increase rather strongly upon forced beer aging, whereas for others (e.g., 2-methylpropanal), large amounts appeared to already be present in a bound state in the fresh samples. Spiking beer samples with cysteine prior to aging significantly lowered the aldehyde levels compared with nonspiked samples. Flavor stability of the cysteine-spiked beers was thereby greatly improved through aldehyde-cysteine adduct formation. It was further hypothesized that, in addition to efficient binding of aldehydes, cysteine also inhibits the formation of furfural during beer aging from Maillard reaction intermediates.
