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How long can I keep ampoules of yeast from the NCYC before they begin to lose viability?

This depends on the conditions that the ampoules are kept in; at normal room temperature (21°C) the freeze dried yeast in the ampoules should remain viable for at least 6 weeks. We would recommend keeping the ampoule away from bright sunlight as this can affect the contents. The preferred method of storage for the ampoules is at 1°C in the dark. Under these conditions the freeze dried yeast in the ampoules should remain viable for many years. The NCYC has strains that have been stored by this method for up to thirty years and we have seen no sign of a drop in viability.

How long can I store live yeast from the NCYC?

Live yeast strains from the NCYC or strains grown from opened ampoules can be stored either in YM broth or on YM agar and will usually remain viable for up to 6 months from initial inoculation if kept at 1-8°C, although the exact time will vary according to the individual strain involved. The live strains can be kept over longer periods by subculturing although care must be taken not to introduce contaminants. We would recommend purchase of a new culture from the NCYC after 6 months to ensure quality and viability are maintained.

How to revive yeast cultures

Rehydration and Growth of freeze dried cultures

Each yeast is dispatched as a small quantity of freeze-dried culture sealed under vacuum in glass ampoules. Ampoules should be opened in the following way:
  1. Check the number on the label inside the ampoule.
  2. Score the glass with a suitable file or scoring impliment at the level of the cotton wool plug.
  3. Wipe the ampoule with alcohol soaked tissue, then wrap the tissue around the ampoule.
  4. Using sufficient padding, apply pressure both sides of the mark and snap the ampoule along the score line. Be careful in this step to avoid a glass stab wound.
  5. Remove the tip of the ampoule and cotton wool plug and place in a sharp container.
  6. Using a sterile Pasteur pipette, add about 0.5ml YM broth (Difco 0711-01) or malt extract to the dried material.
  7. Gently resuspend the dried culture and transfer to a culture bottle containing approximately 10ml of the same medium. 
  8. Unless otherwise indicated, most yeasts should be incubated at 25°C. Growth may be slow immediately after resuscitation. It may be necessary to incubate cultures for at least 5 days before discarding. Growth is usually stimulated by aeration which may be achieved by shaking or rocking the culture.
  9. The discarded ampoule should be placed in a container for subsequent sterilization before disposal.

Growth Media

All NCYC strains (except where indicated) can be routinely grown in YM broth (Difco 0711-01). Other suitable nutrient media include:
  • YM: 0.3% yeast extract, 0.3% malt extract, 0.5% peptone, 1% glucose
  • YEP-glucose: 0.5% yeast extract, 0.5% peptone, 1% glucose
  • Malt Extract: 0.3% malt extract, 0.5% peptone
  • Sabouraud’s Glucose: 1% peptone, 4% glucose
  • YPD medium: 1% yeast extract, 2% peptone, 2% glucose
  • Yeast Nitrogen Base (Difco 0392-15-9): a chemically defined medium to which a carbon source must be added.
  • Yeast Nitrogen Base without amino acids (Difco 0919-15-3), which can be supplemented with appropriate amino acids or other source of nitrogen (useful for some genetically defined strains). A carbon source must be added.
Agar when required is added to a final concentration of 1.5 – 2.0% (All percentages are given weight/volume)

More information about these media is given by J P van der Walt & D Yarrow, ‘Methods for the isolation, maintenance, classification and identification of yeasts’ in ‘The Yeasts . A Taxonomic Study’, third edition by ed. N J W Kreger-van Rij, Elsevier, (1984) pp 45-104, and in ‘Yeasts: Characteristics and Identification’, third edition by J A Barnett, R W Payne & D Yarrow, Cambridge University Press, (2000).

How to revive yeast cultures

How do I choose a yeast strain for brewing a particular type of beer or lager?

Unfortunately most of the brewing yeast have been received on a confidential basis and the depositors or customers who use the strains do not usually give us much feedback on how the yeast worsk as regards giving the final product its characteristics. We are therefore unable to give customers details on exactly which strains in the NCYC have been used to brew particular beers.

It is however usually possible to get a yeast from the collection which matches the charateristics of an older strain using the ‘Tall Tube Codings’ which are given with most of the strains. Our customers usually use these to select a yeast which they think is suitable for their purposes. It is difficult to predict exactly how a yeast will behave and what the character of the final brew will be, since this tends to vary depending on the other ingredients used and the exact brewing process. We usually suggest that a customer picks one or two yeast which look suitable and try trial brews. The full explanation of the ‘Tall Tube Codings’ can be found in the brewing yeast section of the web site.

Does the NCYC sell to home brewers and bakers?

We can supply to home brewers and bakers. However, since we specialise in very high quality starter cultures which are designed to be grown in the lab and bulked up for large scale brewing or baking, our prices tend to be prohibitive for the home brewer.

Which yeast strains do you recommend for the production of bioethanol?

We have a range of strains that we recommend for this purpose, which include NCYC 614 Pachysolen tannophilus, NCYC 1403 Candida succiphila, NCYC 2545 Candida tenuis and NCYC 1541 Pichia stipitis. Further details and associated references about the strains can be found on the website if you type the NCYC number into the culture search. We also have a useful Special Application Search on the culture search page, where you can find strains that for example utilise xylose.

NCYC and Pathogenic yeasts

Pathogenic yeasts and fungi from clinical sources are held at the National Collection of Pathogenic Fungi. In general the NCYC holds non-pathogenic yeasts but there are certain exceptions to this and the following comments are included as a guide to users. It must be noted that pathogenicity is not an absolutely defined characteristic and so the following should be used as a guide rather than a definitive account of the subject.

Many kinds of microorganism may become opportunistic pathogens if they gain access to the human bloodstream. If the subject has an impaired immune system the consequences of such invasion are very serious and may be fatal.

The most pathogenic yeasts are certain Candida species and Filobasidiella neoformans, the asexual state of which is called Cryptococcus neoformans. The latter species is not held by NCYC.

Hurley et al (1987) list the pathogenic yeasts of candidosis in probable descending order of virulence for man as: C.albicans, C.tropicalis, C.stellatoidea, C.glabrata, C.krusei, C.parapsilosis, C.guilliermondii, C.viswanathii, Clavispora lusitaniae (Candida lusitaniae) and Rhodotorula mucilaginosa (Rh.rubra). (Ref: ‘The Yeasts’, Vol 1. ed. A H Rose and J S Harrison. Academic Press, 1987: Chapter 4). However only a few Candida species are markedly pathogenic. Some species of Malassezia, Trichosporon and Geotrichum may also be pathogenic.

A number of other yeast species not mentioned here have also been described as pathogens under particular circumstances and it is advised that a literature search is made if a decision is required on any particular strain or species.

Customers should always employ good microbiological practice when working with yeast cultures and use ‘Category 2’ containment when working with the Candida strains listed above, or any yeast strain suspected of being a pathogen. Full details can be found in: ‘Categorisation of biological agents according to hazard and categories of containment’, Advisory Committee on Dangerous Pathogens, HSE Publications, ISBN 0 7176 1038 1. The NCYC will be pleased to offer advice on suitable containment levels.

Please note that the NCYC is prohibited from sending cultures which are regarded as human or animal pathogens, or that are classified as ‘dual use’ to certain countries.