Words By Celina Dugulin
Dry yeast has shown to be an ideal option to producing great beer. Sterile, simple to handle, readily available, with a shelf-life of up to 3(!) years, and tolerant to sub-standard storage or shipping conditions. The number of dried yeasts available on the market increases every year, however, not all yeast strains can be dried (at least not yet).
But there is simply no end to a brewer’s creativity – being always on the forefront to inventing and re-inventing beer and diving into the world of different flavours and aromas. And hereby the yeast plays a crucial role. Beers will not taste the same if you use different yeast strains, despite fermenting wort (feedstock for yeast metabolism) from the same brew!
The wide range of liquid yeast strains available, range from local to exotic and even historical strains, which can be purchased from a (liquid) yeast supplier, or from a ‘yeast bank’ such as the NCYC (National Collection of Yeast Cultures).
While that sounds easy, there are a few important factors to consider when handling and pitching liquid yeast.
- Keep it clean and sterile. Cannot be emphasised enough!
- Liquid yeast is a live culture. In contrast to dried yeasts, liquid yeast is more susceptible to storage and storage conditions. Always store the yeast under conditions that prevent contamination and minimise any changes in physiological condition, which could compromise the fermentation.
- Keep the liquid yeasts always in the refrigerator (1oC-4oC).
- Do not freeze ‘unprotected’ liquid yeast. Freezing liquid yeast always requires a cryoprotectant (e.g. glycerol) to prevent osmotic lysis (=cell death).
- Avoid long storage times – viability decreases during storage. The storage phase is a period of starvation and can only be pro-longed for a certain length of time, depending on factors such as yeast health, yeast strain, temperature control, etc..
- Some liquid yeasts come in a ‘smack pack’ that needs to be activated at least three hours before pitching.
- Before use check yeast cell count and viability. The number of yeast cells in dry yeast packs is highly concentrated. To ensure the brewer does not under or overpitch, it is recommended to confirm the cell count. In addition, to measure the quality of yeast, it is worth checking yeast viability, particularly when the liquid yeast was stored, or you aim to re-pitch.
- One of the most common ways to count the number of cells in a suspension is with a microscope and haematocytometer. Similarly, the viability can be assessed by staining with methylene blue. Methylene blue readily permeates yeast cells, but it is reduced to a colourless compound in living cells.
- If cell counts are too low for your brew, consider making a yeast starter
- Liquid yeasts require wort oxygenation. Yeasts require oxygen to synthesise unsaturated fatty acids and sterols – essential components of membranes and thus yeast growth. The technique to propagate (oxidative growth) dried yeast, already ensures that the yeast has sufficient quantity of these sterols and unsaturated fatty acids and hence stabilises the cells against the drying process. Consequently, that’s why dry yeasts are capable of growth under strictly anaerobic conditions, allowing several rounds of cell division and thus healthy fermentation. Liquid yeasts, on the other hand, require oxygenation/aeration at the onset of fermentation to develop these components.
PS: When re-pitching yeasts or using dry yeast for fermenting high gravity worts, please oxygenate the wort as well to allow healthy fermentation.
- Consider adding yeast nutrients: For the initial growth phase, yeasts will require important nutrients and trace minerals, essential for a healthy fermentation. Our formulated yeast nutrients (Yeast Vit), provide nutrients which supplement those present in wort to keep this wonderful microorganism healthy and improve fermentation and consistency.
- Acid washing to eliminate bacterial infections: You can consider ‘acid washing’ (pH 2-2.2 using food-grade phosphoric acid) your yeast slurries between fermentations to eliminate bacterial infections. Acid washing kills bacteria (not wild yeasts!) with minimal harm to the brewing yeast, providing that the process is carried out correctly. Improper ‘acid washing’ can significantly reduce yeast viability and vitality. The effectiveness of the process relates to the initial health of the yeast slurry, time and temperature it is carried out, and the pH achieved.
Please contact our technical team for further guidance by emailing techsupport@murphyandson.co.uk
References
Boulton, C & Quain, D 2006. The Biochemistry of Fermentation. Brewing Yeast and Fermentation. https://doi.org/10.1002/9780470999417.ch3
Stewart, G.G., Hill, A.E. and Russell, I. (2013), 125thAnniversary Review: Developments in brewing and distilling yeast strains. J. Inst. Brew., 119: 202-220.https://doi.org/10.1002/jib.104
White, C & Zainasheff, J 2010. Yeast: The Practical Guide to Beer Fermentation. Brewers Publications.