The high loss rate of bread is generally known to contribute to the alarmingly high numbers in worldwide food waste. Correct storage techniques are believed to enable the reduction of preventable food waste. Therefore, the influence of storage parameters on staling and spoilage behavior of German bread within the limits of common household methods was investigated in this study. The aim was to generate reliable data for staling and spoilage using different storage methods (PE-layered microperforated paper bag, plastic bag, and fridge and bread box) to bridge the gap between consumer’s needs and scientific research questions. Everyday routines of life, such as visual inspection, were compared with microbiological techniques and were found to represent an adequate tool for microbial safety control. Visually undetectable fungal growth has not been found to result in the production of mycotoxins (fumonisins B1 and B2 and ochratoxin A) in quantifiable or harmful concentrations. Thus, disgust should prevent any foodborne health risks as the visual appearance should lead to avoiding the consumption of spoiled food before mycotoxins are produced in amounts causing adverse health effects within the limits of this experimental setup. Additionally, the storage temperature especially was found to influence the kinetics of staling processes, as a reduction accelerated the staling process. Further, crumb moisture loss was found to contradict a long shelf life but, on the other hand, an elevated humidity was shown to provoke excessive microbial growth and should therefore be observed when designing suitable storage methods. Further, the correct choice of the bread type stored and a good sanitary practice represent simply accessible ways to prolong the storage period of bread loaves.

Flavor instability of beer is affected by the rise of aroma-active aldehydes during aging. Aldehydes can be either released from bound-state forms or formed de novo. This second part of our study focused on the de novo formation of aldehydes during the Maillard reaction, Strecker degradation, and oxidation reactions. Key precursor compounds for de novo pathways are free amino acids. This study varied the potential for reactions by varying free amino acid content in fresh beer using different proteolytic malt modification levels (569–731 mg/100 g d. m. of soluble nitrogen) of the used malt in brewing trials. Overall, six pale lager beers were produced from three malts (different malt modification levels), each was made from two different barley varieties and was naturally and forcibly aged. It was found that higher malt modification levels in fresh beer and during beer aging increased amino acid and dicarbonyl concentrations as aging precursors and Strecker aldehyde contents as aging indicators. Dicarbonyls were degraded during aging. Advanced glycation end products as possible degradation products showed no consistent formation during aging. Therefore, Strecker reactions were favored during beer aging. No alternative oxidative formation of Strecker aldehydes from their corresponding alcohols could be confirmed. Along with the preceding part one of our investigation, the results of this study showed that de novo formation and release occur simultaneously. After 4 months of natural aging, aldehyde rise is mainly accounted for by de novo formation.

Flavor instability of pale lager beer depends decisively on aroma-active aldehydes from the Maillard reaction, Strecker degradation, and lipid oxidation, which are formed in various oxidative and non-oxidative reactions. Therein, aldehydes can be formed de novo and be released from bound states to a free, aroma-active form during aging. During malting and brewing, proteolysis affects the amount of soluble nitrogen and thus flavor instability in different ways (e.g., precursors for de novo formation and binding agents for bound states). To isolate nitrogen-related aging processes, beers from malts (two barley varieties, three proteolytic malt modifications) were produced on a 50 L scale in part 1 of this study. Sensory analysis revealed increased flavor instability for beers with higher amounts of soluble nitrogen. Especially Strecker aldehydes significantly increased with malt modification. The release of bound state aldehydes revealed most free aldehydes in fresh beers and with higher malt modification. During aging, the equilibrium between free and bound state aldehydes shifted toward the free form. These results reveal a nitrogen-dependent bound pool of aldehydes that is depleted during aging and is responsible for aged aroma, especially in the early and medium stages of aging. Therefore, bound state aldehydes are indicators of the early-stage prediction of flavor instability already in a fresh condition.

The metabolite 3-deoxyglucosone (3-DG) is formed by carbohydrate caramelisation or the Maillard reaction. 3-DG is a precursor in the Strecker reaction forming beer ageing compounds, such as 2-methylbutanal or 3-methylbutanal. Although 3-DG is known as intermediate, recent studies have focused on 3-DG in beer. Foremost, the thermal load during wort boiling provides the best conditions for 3-DG formation and degradation, however, the reactivity of the dicarbonyl during the boiling process has not yet been explained. As a key intermediate, 3-deoxyglucosone could be a critical indicator for beer ageing stability. The 3-DG formation and reactivity during wort production depends on its precursor reactants (amino acids and glucose). The concentration in wort of these substances was varied using two malts with different malt modification along with two different mashing programmes. 3-Deoxyglucosone reactivity was observed by analysing dehydratisation to HMF (HPLC-UV), interconversion to 3-deoxygalactosone (3-DGal, HPLC-UV) and selected Strecker aldehydes (GC-SPME-MS). This study shows that wort boiling is the most important process in 3-DG formation as it contributes 47% of the final content compared with malting (28%) and mashing (25%). With degradation reactions, 3-DG is mainly interconverted to 3-DGal and, contrary to the literature, it could not be confirmed that enhanced 3-deoxyglucosone content affects Strecker reactions. The interconversion reaction during wort boiling determines the dicarbonyl potential of beer and influences the ageing stability. © 2021 The Authors. Journal of the Institute of Brewing published by John Wiley & Sons Ltd on behalf of The Institute of Brewing & Distilling.