Mead production: Selection and characterization assays of Saccharomyces cerevisiae strains Ana Paula Pereira a , Teresa Dias a,b , João Andrade a,b , Elsa Ramalhosa a,b , Letícia M. Estevinho a,b, * a CIMO, Campus Santa Apolónia, Apartado 1 172, 5301-855 Bragança, Portugal b Escola Superior Agrária, Instituto Politécnico de Bragança, Campus Santa Apolónia, Apartado 1 172, 5301-855 Bragança, Portugal abstract Mead is a traditional drink, which results from the alcoholic fermentation of diluted honey carried out by yeasts. However, when it is produced in a homemade way, mead producers find several problems, namely, the lack of uniformity in the final product, delayed and arrested fermentations, and the produc- tion of ‘‘off-flavours” by the yeasts. These problems are usually associated with the inability of yeast strains to respond and adapt to unfavourable and stressful growth conditions. The main objectives of this work were to evaluate the capacity of Saccharomyces cerevisiae strains, isolated from honey of the Trás-os- Montes (Northeast Portugal), to produce mead. Five strains from honey, as well as one laboratory strain and one commercial wine strain, were evaluated in terms of their fermentation performance under eth- anol, sulphur dioxide and osmotic stress. All the strains showed similar behaviour in these conditions. Two yeasts strains isolated from honey and the commercial wine strain were further tested for mead pro- duction, using two different honeys (a dark and a light honey), enriched with two supplements (one com- mercial and one developed by the research team), as fermentation media. The results obtained in this work show that S. cerevisiae strains isolated from honey, are appropriate for mead production. However it is of extreme importance to take into account the characteristics of the honey, and supplements used in the fermentation medium formulation, in order to achieve the best results in mead production. 1. Introduction Mead is a traditional drink, containing 8–18% (v/v) of ethanol, which results from the alcoholic fermentation of diluted honey car- ried out by yeasts. Mead fermentation is a time-consuming pro- cess, often taking several months, and the fermentation rate depends on several factors, especially on honey variety, yeast strain, yeast nutrition, control of pH (Navrátil et al., 2001). Honey is a natural product, mainly composed of a complex mix- ture of carbohydrates and other minor substances, such as organic acids, amino acids, proteins, minerals, vitamins, and lipids (Finola et al., 2007). In almost all honey types, fructose and glucose pre- dominate. These two sugars account for nearly 85–95% of the hon- ey carbohydrates (Finola et al., 2007). However, the composition of honey is rather variable and primarily depends on the floral source; in addition, certain external factors also play an important role, such as seasonal and environmental factors, as well as the processing method (Arráez-Román et al., 2006). Some reports show possible correlations between floral origin and flavonoid pro- files (Anklam, 1998; Yao et al., 2004). In relation to honey colour, it depends on the potential alkalinity and ash content, as well as on the antioxidatively active pigments, such as carotenoids and flavo- noids (Baltrušaityte ˙ et al., 2007). Honey production is an activity with significant economic importance in several regions of Portugal. However, nowadays in the northeast of Portugal, there is an excess of honey that is being sold below production prices, making it imperative to found new ways to make apiculture a viable enterprise. One possible solution for this problem could be mead production. However, when it is produced in a homemade way, the beekeepers and mead produc- ers find several problems, namely, lack of uniformity in the final product, since the water content of honey changes every year, (20% maximum, except for Calluna honey which is 23%) (Decreto- Lei n° 214/2003 de 18 de Setembro), that can induce not only ref- ermentations by yeasts, but also metabolisation of residual sugar by acetic acid bacteria and lactic acid bacteria. This increases vola- tile acidity and produces abnormal esters, changing the organolep- tic quality of the final product (O’Connor-Cox and Ingledew, 1991). Delayed and arrested fermentations are other problems found in mead production, causing significant delays in the marketing of mead, being sold one year after its production. Finally, the stages of clarification and filtration, that are desirable, make the produc- tion process extremely expensive. In wine production, some similar problems are also encountered. Delayed and arrested fermentations, as well as the * Corresponding author. Address: CIMO, Campus Santa Apolónia, Apartado 1 172, 5301-855 Bragança, Portugal. Tel.: +351 273 303342; fax: +351 273 325405. E-mail address: leticia@ipb.pt (L.M. Estevinho).