Water kefir (WK) is an artisanal fermented beverage made from sugary water, optional fruits and WK grains. WK grains can be reused to start new fermentations. Here we investigate the microbial composition and function of 69 WK grains and their ferments by shotgun metagenomics. A subset of samples was subjected to metabolomic, including volatilomic, analysis. The impact of different fermentation practices on microbial composition and fermentation characteristics was analysed and it was noted that, for example, the common practice of drying water kefir grains significantly reduces microbial diversity and negatively impacts subsequent grain growth. Metagenomic analysis allowed the detection of 96 species within WK, the definition of core genera and the detection of different community states after 48 h of fermentation. A total of 485 bacterial metagenome assembled genomes were obtained and 18 putatively novel species were predicted. Metabolite and volatile analysis show associations between key species with flavour compounds. We show the complex microbial composition of WK and links between fermentation practices, microbes and the fermented product. The results can be used as a foundation for the selection of species for large scale WK production with desired flavour profiles and to guide the regulatory framework for commercial WK production.

Terroir refers to the combination of environmental factors, such as climate, soil, and agricultural practices, that shape the characteristics of a crop, contributing to the unique qualities of the final product. The concept has been traditionally linked to wine, but some recent findings suggest that it also holds importance for distilled spirits. The expanding Irish distilling sector is shifting towards local raw materials such as wheat and rye, driven by regulatory changes, economic benefits, and consumer demand for sustainable local products. This research examines the effects of wheat variety, geographical location, and harvest year on grain composition and volatile composition of the new make spirit. For this study, twenty lab-scale wheat whiskey samples were produced from five different wheat varieties grown at two different locations in Ireland over two consecutive years. The wheat samples were analysed for grain composition and the volatile profiling of new make spirit samples by headspace solid-phase microextraction (HS-SPME) followed by gas chromatography–mass spectrometry (GC-MS). A total of fifty-one volatile compounds were detected, with ethanol, ethyl acetate, phenyl ethyl alcohol, and 3-methyl-1-butanol being predominant. Principal component analysis revealed that both the harvest year and geographical location moderately influenced the volatile compound distribution of the new make spirit, which is explained by a 43.25% variance. ANOVA analysis revealed that grain composition was significantly influenced by harvest year, location, and wheat variety. The 2020 samples showed higher protein and β-glucan content, whereas samples from the location Tipperary had higher starch content. This study indicates that terroir—specifically seasons (year) and geography (location)—affects the characteristics of wheat-based Irish whiskey, highlighting opportunities for distillers to differentiate their products by leveraging local environmental factors.

Milk and water kefir are fermented beverages prepared by inoculating milk or sugar-rich solutions with kefir grains - containing complex microbial consortia of bacteria and yeast. The increasing global popularity of kefir has driven interest in their microbiomes. Beyond their culinary significance, kefir serves as a model system for studying microbial community assembly, ecological filtering, and evolutionary dynamics. Kefir’s suitability as a model is enhanced by its simplicity (including short fermentation times), adaptability to experimental manipulation, and scalability for both controlled laboratory studies and citizen science initiatives. In this study, we employed genome-resolved metagenomics to investigate milk and water kefir microbiomes, produced over 21 weeks from an initial common source milk or water kefir grain by citizen scientists, using diverse substrates and conditions. Early fermentation (weeks 1–9) was marked by rapid compositional, functional and volatile shifts, leading to reproducible transitions between community states, with values not changing considerably thereafter. At the strain level, we identified multiple coexisting strains within dominant species, with initial fluctuations. While rare environmental species occasionally appeared, they were selectively filtered and did not persist. The sustained coexistence of key species and strains, alongside the emergence of reproducible community types, highlights the resilience and stability of kefir microbiomes across both short- and long-term timeframes. Our findings reinforce kefir’s value as a model for investigating microbial interactions, environmental microbial acquisition, and strain-level dynamics. The co-occurrence patterns observed among specific strains and species provide insight into microbial assembly and persistence, with broader relevance to complex ecosystems such as the gut microbiome. By elucidating patterns of compositional and functional change and assessing how selective pressures shape microbial communities, this study underscores kefir’s utility in microbial ecology and evolution.

The volatile profiles of beef steaks (Longissimus lumborum) were analysed both raw and grilled to five different internal temperatures, 55 °C, 60 °C, 71 °C, 77 °C, and 85 °C, representing very-rare, rare, medium rare, well-done, and very well-done, respectively. Volatile organic compounds (VOCs) were extracted using direct immersion high-capacity sorptive extraction (DI-HiSorb) and analysed by gas chromatography–mass spectrometry (GC–MS). A total of ninety-one VOCs were detected with forty-two significantly impacted by the degree of doneness, thirty of which had Variable in Projection score > 1. Principal Component Analysis produced three distinct clusters, (i) raw, (ii) very-rare, rare, and medium-rare, (iii) and well-done and very well-done. Direct immersion high-capacity sorptive extraction (DI-HiSorb) provided a comprehensive volatile profile of grilled beef steak across different degrees of doneness and revealed that the abundance of methyl esters. The main findings were that in relation to the degree of doneness methyl esters were significantly reduced, with both aldehydes and pyrazines increasing due to thermal lipid oxidation, Strecker degradation, and Maillard reaction, highlighting the significance of internal temperature on the volatile profile of steak during grilling.