Yeasts conserved at 4°C under lyophilized form are generally viable for a few years. Under these conditions the problems of genetic instability are undoubtedly quite insignificant. On the other hand, lyophilized strains must be revitalized before use. In order to reduce yeast cell mortality, the freezing of yeast biomass before vacuum drying procedure can be done very rapidly (e.g. by using liquid nitrogen at – 196 °C or, alternatively, a – 80°C freezer).

The DBVPG collection can prepare batches of lyophilized ampoules of strains upon request. These can then be either returned to the customer or conserved at DBVPG.

Fundamentals

In order to avoid osmotic stress, dried yeast cells must be revitalized by using suitable media. On the whole, the revitalization procedure warrants a good viability of dried cultures. After revitalization, yeast cultures should be generally newly isolated by striking them onto the surface of an agarized medium (e.g. YEPG agar).

Media and test procedure:

Working under laminar flow cabinet

• take an ampoule containing the dried culture and break the inner part by removing aseptically the inserted sterile cotton plug
• introduce 0.5 ml ca of YEPG broth (yeast extract 10 g/l, peptone 10 g/l, glucose 20 g/l) into the ampoule by using a Pasteur pipette and mix carefully
• after a few minutes, transfer the cell suspension into a test tube containing 5 ml of the same medium and incubated the culture at 25°C for 2-5 days, under shaken conditions (e.g. in a roller drum).  In the case of psychrophilic yeast strains, the incubation should be done at 4°C for 1-2 weeks
• check periodically the presence of yeast growth on test tube
• after growth, streak the revitalized yeast cell culture onto the surface of a suitable agarized medium (e.g. YEPG agar) and incubate the Petri dishes under the same conditions reported above.