photo: Kaetsu Shuzô president Shunichi Satô with yeast (in solution)
text: by John Gauntner
A sake’s aroma might be described as its kanban-musume, a term that refers to a charming young woman that attracts the attention of passers-by and draws potential customers into a store on a busy shopping street. This is especially the case with modern ginjô and daiginjô. While sake is much more than its aromas, usually they are the first thing we encounter when gauging the beverage. It’s what gets our attention and draws us into the flavors, complexities and character.
If you like the way your sake smells, you can thank the yeast. Do you smell melon? Thank the yeast. More like banana? That comes from a different yeast. How about apple, licorice or pineapple? Again, a result of the choice of yeast strain.
Until the late 1800s, all yeast used in sake brewing came from the ambient environment, dropping into the tank naturally. In fact, the quality and reputation of a sake often owed to the yane-tsuki kôbo, or the resident yeast within a brewery–the stuff clinging to the rafters and floating about in the air. Back then, there was but one yeast per brewery, a matter over which they had no control. It was just the luck of whatever strain lived there.
Then microscopes and other technological developments helped sake researchers isolate and identify different yeasts, and make them inexpensively available in pure, cultured form to the industry. This lead to better, more consistent product which benefited all involved, especially the government since taxes on sake were a major part of their tax revenues back then.
The main function of yeast is, of course, producing alcohol. Enzymes from the kôji convert starch in rice to sugar, and yeast then converts that to alcohol (and carbon dioxide). Yeast also yields several types of acid that contribute to the body and texture of a sake. But most significantly, under the proper brewing conditions yeast will give rise to esters, which express the various fruity aromas present in premium sake.
As far as we sake drinkers are concerned, more than anything else, yeast will most assertively express aromas. In truth, what happens in a fermenting tank of sake is much more complex and interdependent than I’m portraying it here. Aromas are also affected by the choice of rice, its milling rate, the temperature of fermentation, just how the kôji was made, and many other factors. Nevertheless, the choice of yeast will still trump all these in determining aroma.
Note, too, that there are other technical reasons one yeast might be better suited to a particular brewing situation. How vigorously a given strain ferments, how long the yeast will work before it peters out, and how high the alcohol can rise in a tank before the yeast dies are just a few more factors dictating yeast choice. Throw in the amount of acidity it produces and its affinity with water types and rice varietals, and you have a complex set of factors governing the yeast selection.
From 1935, a sake research group called the Nihon Jôzô Kyôkai, the official English name of which is the Brewing Society of Japan, began to distribute stable, pure yeast cultures to sake breweries that sought them. The organization remains today the main supplier of yeast strains to the sake-brewing industry. It offers a range of yeast strains known unofficially as Kyôkai-kôbo (the Society’s yeasts) that can be chosen for the aromatics they create, as well as the technical characteristics mentioned above.
For decades, the Jôzô Kyôkai was the only yeast game in town. But today there are many other suppliers of yeasts for brewers. There are also countless strains of yeast used in sake brewing today. Most have names and traceability behind them, and some even have DNA analyses as well. Others are proprietary, having been discovered in a particular brewery, and used only there.
The Kyôkai yeasts are easily recognizable since they are identified by numbers indicating the order in which they were discovered. Those most commonly seen are No. 6, No. 7, No. 9, No. 14 and No. 18-01 (the -01 suffix indicates a low-foaming version; more about this in a future issue of Sake Today!). Others of note include No. 10, No.15, No. 16 and No. 19, but they are less commonly seen.
Again, beyond the Kyôkai family of yeasts, there are many others; it seems like everybody’s got a yeast gig these days. Trying to catalog them here would be an exercise in futility. Who develops these, and why? More to the point, if the range of Kyôkai yeasts is that good, why develop others? Why fix what isn’t broken?
There are a handful of reasons, including regions and prefectures seeking ways to make the sake of their region special and unique. Regional distinction in sake–similar to the concept of terroir–lost much significance due to the homogenization of styles that has taken place over the last 50 years. Yeasts used by local brewers, and nowhere else, can help bring some of that terroir back. Also, national and regional tasting competitions pit the best sake from each brewery against each other, and very often aromas are what determine which stand out and win medals. Therefore, yeast selection plays a huge role in these competitions.
To some degree–and with some boundary conditions and lots of practice–it is possible to identify the characteristics of the major yeast strains, and also to identify which yeast has been used based on the aromas alone. If a sake was brewed in such a way as to maximize the typical characteristics of each yeast (which is never a given!), you probably have a better chance of making the identification.
Perhaps the most iconic examples would be faint banana from yeast No. 7, banana and melon from No. 9, and apple and licorice from No. 18-01. Those strains are a fun and easy place from which to begin studying yeast. Just branch out from there if you can.
Also, for the Kyôkai yeasts only, a very general but useful rule of thumb would be: the higher the yeast number (i.e. the more recently discovered the strain of yeast), the more aromatic the sake. It will have less acidity as well. A sake made using No. 9 will be more aromatic than one made with No. 7, and one made using No. 18-01 would be more fragrant still. Furthermore, due to this quality, the higher the number the sooner (fresher) you should drink it. Otherwise, the aroma will wane. Conversely, the lower the number, the more settled the aromas, the fuller the flavor, and the more prominent and supporting the acidity will be. While few would outright disagree with this categorization, it is far from hard science and there are many exceptions to it. I hope it is a helpful generalization.
Complicating the challenges in learning about yeast is the fact that brewers have no obligation to note on the label, or anywhere else, the yeast that was used. With a bit of poking around on the internet, or asking around, such information is almost always discoverable. Still, there are a very few that will keep that information to themselves.
Why would a producer do that? It may be that it is a yeast they received unauthorized from a friend at another brewery. Or it may be a proprietary yeast that has no name. A brewer may also want to create an aura of mystique, and hiding information always contributes to that. Others want to avoid too much attention on the yeast and that kanban-musume effect.
Such brewers strongly believe that the yeast is only one facet of all that has gone into making a sake what it is, with the other aspects of the brewing process holding just as much significance. They prefer to keep the name of the yeast under wraps, and thus avoid preconceptions of how a sake might taste or smell based on the yeast information.
So what’s a sake fan to do? With all this vagueness and uncertainty, how can we proceed to learn about sake yeasts? The easiest and best place to begin is with whatever sake you have before you. Sniff it. Swirl it. Sniff it again. Taste it. What aromas do you notice–in particular, what fruity aromas? Write those down. Note the yeast as often as possible, and begin to associate fragrances and nuances with the many varieties of yeast. It won’t be long before you develop a feel for what to expect from the main types of yeast used in sake brewing. Yet, with so many out there, our work is never done.
