The first issue of the Japanese Exotic Mushroom Journal glossed over many factors, including business ones, that impact shiitake cultivation, but substrate is an issue worth returning to. I recently had the opportunity to tour one of the largest shiitake production facilities in the Tohoku region in northern Japan, Mizu Dori, which grows over 400 metric tons of shiitake a year. In addition to Mizu Dori, I have also spent time recently at a shiitake spawn maker’s facility and have continued throughout this year to parse through different avenues of information. The challenging part is dealing with the abundance of highly detailed but variant information on shiitake cultivation in Japan_emdash_that for the most part has not been widely disseminated abroad, piecing together the picture among half-answers and often cryptic hedging from figures in the industry.

At Mizu Dori, as at prior trips to major shiitake growing facilities in Gunma Prefecture, I noted the use of a very fine sawdust alongside a rougher wood chip mixture, at a roughly 60-40 ratio. This widespread feature may improve overall yield or slightly reduce incubation time, but I have not yet found anyone who could explain why they do it and how it impacts cultivation, so I will set that particular trait aside for the time being. Mizu Dori, in a first among all the sites I have toured, used an all-oak sawdust mix, and for nutrition supplements, relied on a premixed supplement from their spawn maker, which they would not be able to give me any details on even if they knew them (they did not). This follows the first issue’s shiitake article, wherein I explained how spawn makers charge approximate four times the price for spawn in the U.S. and EU, but offer very detailed total support packages and meticulously monitor and test for quality from every batch, even issuing recalls when they detect problems in a batch. Mizu Dori’s representative explained to me that they used to mix nutrition supplements themselves, but eventually stopped because if the ratio of rice bran to wheat bran was slightly off, they would either get too few pinnings or far too many, and the spawn maker’s recommended mixture offered much better stability and function at a competitive price.

Japanese shiitake growers generally add some form of calcium to the substrate, whether it be lime or calcium bicarbonate or another approximate substitute. The reason for this is not that calcium is a useful nutrient for shiitake or that it facilitates enzymic reactions within the substrate during cultivation. The use of calcium in shiitake substrate is perhaps one of the less understood elements of shiitake cultivation abroad, but in simple terms, calcium is a good pH regulator. The substrate mixture of each batch of substrate blocks is tested for total water content and pH the morning the filling machines and mixers are turned on. Growers typically aim for a water content between 61~63%, and more importantly, a pH between 5.5 and 6. If the starting pH has fallen to 5, it will continue falling during incubation, which negatively impacts mycelial growth. pH can fall below 4, and in such cases many blocks experience pinning failure. Mizu Dori’s representative explained that heat and humidity increase the need for a pH regulator, and that in summer, they incrementally adjust the amount of lime used, based on the pH readings they are getting pre-fill. Growers who have experienced sudden pinning failures on shiitake made from substrate blocks filled during a heat wave (though given the three months of incubation in between, such patterns may not be readily obvious) have likely suffered from a case of poorly regulated pH. The question of how much calcium to add to substrate though, is not as simple as answering why it is added and what it does, as Mizu Dori noted their quantities increase during hot months. What form of calcium, lime or a different calcium compound, the sawdust in question (grain size, freshness, tree variety, sugar content) and contemporary weather conditions as well as the other nutrition supplements all play a sizable role in adjusting the relatively minuscule (when I visited a spawn maker, they used less than .003% calcium bicarbonate in terms of the substrate’s total weight) amount of calcium used. Every grower should test for pH before filling, record that data, and then make decisions on, for instance, whether a pH regulator is even needed. Not every grower in Japan adds a regulatory agent, and if the sawdust is fresh and climatic conditions ideal for shiitake cultivation, adding calcium may raise the pH too much and negatively impact the ability of the mycelia to break down the substrate, leading to smaller yields.

Likewise, most Japanese practices in shiitake cultivation are inexorably intertwined with the need to harvest subsequent flushes. In Japan, shiitake cultivation typically continues through the third flush with all-sides cultivation, and often even a fourth flush. This is a major difference between shiitake cultivation in Western markets, where it is typical to only harvest a first flush. The reason why boils down to different cost calculations. Mushroom cultivation sawdust is expensive in Japan, energy is also very expensive, and increasingly so, in Japan (among the highest prices in the world), and spawn itself costs around four times as much as in Western markets. Meanwhile labor is cheap and extremely productive_emdash_veteran pickers can average around 40 kg (90 lbs.) of shiitake an hour, and hourly wages are rarely higher than 1000-yen, or around 9 USD in terms of real purchasing power. The Japanese math on the business side is simply different and taking into account the cost of sawdust, the energy involved in sterilization and the first and second incubations, and the cost of the cultivation bags and spawn, means even large-scale growers need to harvest anywhere from 750~850 grams of shiitake from a block just to break even. Recall that very small shiitake, malformed shiitake, and opened shiitake are difficult to sell and generate smaller margins, and the need to harvest as much shiitake from each block as possible makes even more sense. On the contrary, throwing away substrate blocks after the roughly 500-gram first flush doesn’t make business sense for growers in Japan. Thus, Japanese shiitake growers rest blocks for approximately two weeks while regularly spraying them with water, then place them into drums or boxes and submerge them in water for 6~8 hours before taking them out and placing them on racks and back into growing rooms. While this section of the growing process requires some difficult physical labor (but less labor than it takes to fill bags, sterilize them in an autoclave, inject spawn, oversee the incubation process, then remove substrate blocks from cultivation bags after browning), and the yield of 250~300 grams is less than the first flush, the energy expenditure is considerably less. What’s more, the bottleneck on the shiitake cultivation process is the long incubation and the space and energy it requires. In addition, the sterilization and inoculation process, where the machinery and facilities involved are very expensive and difficult to scale up, is another bottleneck even for growers of considerable size. It's easy to build a new greenhouse to house second and third flush substrate blocks, but expensive to expand clean rooms for spawn injection on top of purchasing additional inoculating machines and autoclaves. Mizu Dori’s Chairman explained very frankly that the company breaks even on labor costs for subsequent flushes as long as the yield per block is greater than 50 grams. In other countries operations with more expensive and/or less productive labor, even a yield of 250 grams may not generate a profit.