Yeast is unicellular (single-celled) microorganism and produces by budding. Also known as fungi, yeast can convert sugar to form alcohol, along with other by-products. As of now, hundreds of yeast varieties have been found. For beer production purposes, the two main kinds of yeast used include ale yeast and lager yeast.
The Latin name of ale yeast is Saccharomyces Cerevisiae. It has been used since ancient Egyptian evolution times. Ale yeast for re-fermentation offers a unique flavour to the beer, which is devoid of the phenolic taste (as can be found in case of lager beer yeast). It is so because these yeasts undergo natural mutation and hence do cause the occurrence of undesired tastes. Ale yeasts offer all benefits to the beer brewers. They work on the right sugar profiles, ferment fast and quick, survive the anaerobic conditions, and also tolerate alcohol levels to a great extent.
Ale yeasts for re-fermentation include the Belgian strains, wheat strains, and many others. The performance of these yeasts may differ from each other in flocculation, attenuation, and in other areas. Hence, they can be used for producing different flavours. However, they have some similarities, as well. For instance, many of the ale yeast varieties have the fermentation temperature at around 68°F. They may tolerate heat up to 95° F. Clean fermenters are those that produce less of flavours. They are quite popular as they produce lager-like beers. Some may produce fruitier flavours, as they have more fused alcohols and esters.
Lager yeasts perform well at the cold temperatures, at around 50 to 55° F. Ale yeast beers did not have a long shelf life as wild bacteria, and yeast also grew. The new lager varieties had a better shelf life. Therefore, they’re much more profitable to produce and provide for higher profits. The first lager yeast variety was isolated in the year 1881, by Emil Christian Hansen, in Carlsberg Laboratories. The techniques of pure-culture developed at that time are still in use in many microbiology laboratories. This yeast was also stored and preserved for long periods by using agar and wort. That is why the lager beer yeast was sent throughout the world successfully, and lager beer re-fermentation is now widespread in all continents of the globe. Unlike ale yeasts, the lager yeasts are bottom fermenters, which means that the lager yeast does not deposit on the top of the tank during fermentation. The “lager” effect is derived when the yeast stays inside the suspension for an extended period. Ageing provides for a reduction in sulfur as well as diacetyl levels, which may get produced during the long and slow fermentation process. When fermentation occurs at colder temperatures, lesser of esters and fused alcohols are produced, which results in a more significant effect.
European wheat beers also produce a variety of flavours, which may include clove, phenolic and wild yeast. They also may consist of butterscotch and the banana esters. Because the wheat beers also produce sulfur, it is essential to do full fermentation, and capping should be done subsequently. Some brewers may cap early to trap carbon-di-oxide, for carbonation purposes. However, the sulfur will stay when this procedural course is adopted. Flocculation maybe not that good for wheat beers.
The Belgian beer yeast variety is also quite comprehensive. You may get types including clove, phenol, esters, fused alcohols, and some earthy flavours as well, after re-fermentation. Belgian brewers use a lot of creativity for the beers they brew, and cleaning and science make an excellent and rewarding part of the brewing process.