Baking with wild yeast in Japan

As in the UK and the US, the usual practice for most bakeries and pizza restaurants in Japan is to make dough using baker's yeast, in dry or fresh "生/nama" form:

Some of the instant and dry yeasts available at Nissin supermarket

Baker's yeast comes from a single species called saccharomyces cerevisiae, which produces a reliably standard product and does so quickly, whereas a starter made with natural wild yeast will likely contain multiple types of yeast along with beneficial bacteria, and requires longer to leaven bread. In a nutshell, the argument in favour of using natural yeast over baker's yeast is that thanks to the longer fermentation the bread produced is healthier and better tasting, with layers of flavour and character to enjoy much like a nice wine.

Though baker's yeast is the norm then, if you look carefully at labels you'll notice that quite a few international bakeries around like Paul, Maison Kayser and Andersen and some smaller artisanal Japanese bakeries such as Nemo and Levain have at least a selection of breads with 天然酵母/natural starter on the label. A chap working at Paul proudly informed me that even their 食パン/shokupan (the standard Japanese bread, which is a sweetish 1940's American style white loaf, often pre-cut into very thick spongy slices) is made with levain.

天然酵母/tennnenkoubo (natural starter) and ルヴァン/ruvan (levain/leaven) are used fairly interchangeably in Japanese, though I've seen 天然酵母 used more frequently.  天然 is "natural" and 酵母 is "leaven" which, incidentally, includes the kanji character for 'mother' (母), a common and evocative synonym for starter in many languages. If you see イースト/iisuto (yeast) on the label, then it probably includes some form of baker's yeast.

I've yet been able to buy sourdough bread itself (which I've seen written サワードゥ and サワード) in Tokyo. Some commercial breads include サワー類/sawaa rui (sour items) on the label, but will then also include baker's yeast and so most likely hasn't been made with long leaven time, and lacks the complexity of flavour. I'm sure it's out there though!

In terms of home-baking, where most English speaking communities working with natural yeast have starters that were created using flour and water, the most common way of making a starter from scratch in Japan is to use water and dried fruit, like in this video.

Raisins, apple or strawberries etc. are kept for a few days with water in a clean glass jar, sometimes mixed with a little sugar or honey, until the mixture starts to ferment. The water can then be mixed with flour and used to create a starter for making bread. Yeast is present on the skins of the fruit and in the air, and the fruit itself can add a tint to the crumb and a delicate fruity flavour. Another benefit of using this method would be that if you want to do gluten-free baking, if you can get the fermented water to leaven your gluten-free flour/rice flour etc., then your starter and bread will be completely wheat-free.

This fruit and water method does have its detractors though. It doesn't always work reliably - the yeast and bacteria that thrive on the fruit skin are different to those that thrive best on wheat, and so the idea is that starting off with flour will give you the best type of yeast suitable for leavening flour-based dough, and the best results. The method people choose to use is also probably somewhat a matter of preference and habit.