Characterization of Old Wine Yeasts Kept for Decades under a Zero-Emission Maintenance Regime

Abstract

All laboratories dealing with microbes have to develop a strain maintenance regime. While lyophilization based on freeze-drying may be feasible for large stock centers, laboratories around the world rely on cryopreservation and freezing of stocks at −80 °C. Keeping stocks at these low temperatures requires investments of several thousand kW/h per year. We have kept yeast stocks for several decades at room temperature on agar slants in glass reagent tubes covered with vaspar and sealed with cotton plugs. They were part of the Geisenheim Yeast Breeding Center stock collection that was started in the 19th century, well before −80 °C refrigeration technology was invented. Of these stocks, 60 tubes were analyzed and around one-third of them could be regrown. The strains were typed by sequencing of rDNA PCR fragments. Based on BlastN analyses, twelve of the strains could be assigned to Saccharomyces cerevisiae, two to S. kudriavzevii, and the others to Meyerozyma and Candida. The strains were used in white wine fermentations and compared to standard wine yeasts Uvaferm/GHM (Geisenheim) and Lalvin EC1118. Even with added nitrogen, the strains exhibited diverse fermentation curves. Post-fermentation aroma analyses and the determination of residual sugar and organic acid concentrations indicated that some strains harbor interesting flavor characteristics, surpassing current standard yeast strains. Thus, old strain collections bear treasures for direct use either in wine fermentations or for incorporation in yeast breeding programs aimed at improving modern wine yeasts. Furthermore, this provides evidence that low-cost/long-term culture maintenance at zero-emission levels is feasible.

Snails as Taxis for a Large Yeast Biodiversity

“…The ethanol levels produced by these strains were substantial thus raising an interest in these strains for low-alcohol fermentations. Interestingly, the amount of malic acid was found to be lower (less than half) and thus more preferable compared to what is normally found in fermentations carried out with wine yeasts (see [35] for comparison). We also analysed several aroma compounds via gas chromatography.…”

“…Chemical analysis at the end of the fermentations included HPLC (High-Pressure Liquid Chromatography) quantification of several compounds including fructose, glucose, ethanol and organic acids; aroma compounds were analysed by GC (Gas Chromatography) as described in Matti et al [35].…”

“…Fermentations were run at 18 • C under constant stirring at 300 rpm conveyed by a magnetic stirrer. Fermentations with the wine yeast EC1118 were done using Ankom devices as described [35].…”

Yeast Biotechnology 3.0

“…Before cryopreservation was an established method to store wine yeasts, strain collections were stored at room temperature on agar slants in glass reagent tubes covered with vaspar and sealed with cotton plugs. Matti et al [6] characterized 60 strains from the old wine yeast collection from the Geisenheim Yeast Breading collection and confirmed the suitability of storing yeasts by this old method. White wine fermentations and post-fermentation aroma analyses were performed.…”