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Rethinking Shiitake
Looking at Cultivation in Japan
Japanese people are usually quite surprised when they hear the most popular exotic mushroom variety in the West is shiitake. This is because shiitake doesn’t fit the Japanese image of Western cuisine, especially given its use in many traditional Japanese dishes. Children often pick out shiitake in their meals, leading to some growers to report that shiitake is more suited “to an adult's palate.” In taste and texture, shiitake are indeed different from the Agaricus varieties and the wild-foraged mushrooms with which Western consumers are most familiar. When it comes to product, shiitake and other exotic varieties are often mistakenly believed to be uniquely challenging and expensive to cultivate compared to classic button mushrooms. Shiitake are in fact the second-most grown mushroom variety after Agaricus, which is not surprising given their extensive health benefits, and complex umami flavor.

Among the questions directed at the Japanese Exotic Mushroom Journal from mushroom growers outside of Japan, those dealing with shiitake cultivation are most common. Everyone wants to grow more shiitake faster and cheaper. Abroad, growers have an image of Japan as growing shiitake more efficiently or somehow getting larger yields, and so assume there must be some part of the process non-Japanese farms are missing. There are two main categories the inquiries fall into: 1) what kinds of sawdust work best for shiitake cultivation, and 2), supplementation. The answer is, unfortunately, that it’s complicated. How complicated? Well, first we must understand how Japanese spawn companies operate. On average, spawn costs 3~4 times as much in Japan as it does in Europe and America. Japanese spawn makers have a business model that is less about churning out as much spawn as cheaply and quickly as possible, and more about offering total support packages with their specialized spawn, each designed for a particular niche or aesthetic (size, delayed cap opening, etc.).

Thus, a Japanese spawn maker operates more like a mushroom research laboratory that makes spawn as a side business to fund its research. What this means is that each company has multiple strains of spawn, and continually tests a certain percentage of spawn from each batch, keeping meticulous records of all parameters to detect signs of spawn degradation or failed batches. Some companies focus on log cultivation, others on bag cultivation, and the strains and production process for each are wildly different and not interchangeable. There are many varieties of shiitake spawn on the market for growers in Japan, with a wide range of special traits and peculiarities, and all trademarked by their producers, who continually cross-breed with newly harvested wild strains and test the resulting spawn for favorable characteristics in their never-ending search for the next product line. These spawn makers test for even minute differences among the major variables, such as substrate medium, supplementation, inoculation and fruiting room temperatures. Japanese mushroom spawn may be expensive, but it comes with a full user manual for optimal harvests, and the companies take full responsibility for spawning failures where the grower was fully compliant with the spawn instructions. The flipside is that there is a fairly wide variation in “best practice”, and for spawn makers and growers alike these are closely-guarded business secrets.

Spawn makers, when consulted on what kinds of practices are commonplace in contemporary Japanese shiitake cultivation, hedged their bets, saying “Well, for some of strains a certain wood and supplementation works best, but which negatively impacts another strains yield.” The underlying opinion was that without knowing exactly what strain is being cultivated, it is basically irresponsible to make very specific prescriptions for growing methods beyond the general parameters of shiitake cultivation. Happily, this is the researcher's answer, not so much the grower’s reality, and there is generally applicable practice. Every grower has to compromise somewhere, as a researcher’s “ideal” set-up may work fine for 50 substrate blocks managed full-time by a shiitake specialist until harvest, but prove less than realistic for a business churning out 2000~4000 substrate blocks a day and only 50~70 employees (most of whom are not specialists) to manage the entire process.

However, it is true that pH levels, other supplements, and even general parameters such as carbon dioxide levels can have (very) small variations by strain, and those strain-specific details aren’t about to given out for free, nor are they necessarily going to improve every strain's yields. But beyond those general parameters, shiitake cultivation is a matter of practical testing, through trial and error, to establish methodologies that work for a grower’s resources, such as their facilities, local climate, available sawdust, and, something which cultivation guides often elide over: their business model. Whether a grower is selling shiitake for 8.25 USD/kg to a retail wholesaler, or whether they are selling organic-certified shiitake to specialty markets for 15.00 USD/kg is going to make far more of a difference to their growing practices than anything else, spawn, climate, and sawdust included.
Using Japan as a Model
The unexciting reality is that there is no one secret formula in Japan for cultivating shiitake and getting large yields while reducing costs. If anything, shiitake cultivation is in some ways more costly and challenging in Japan than in Western markets. Japan has numerous strains and cultivation methods, making it a rich topic of discussion, but one that requires a lot of contextualization. Shiitake cultivation could fill an entire book by itself and for this journal’s purposes and space constraints, a step-by-step practical explanation of shiitake cultivation_emdash_something that a simple Google search can provide_emdash_is unnecessary. The opening edition of the Japanese Exotic Mushroom Journal will instead document how shiitake cultivation works in Japan, because there are many quirks of the industry here that inform practice. Simply put, in order to judge whether certain cultivation practices would be beneficial or not, it is as necessary to know the “why” as it is to know the “how” otherwise growers risk mis-applying cultivation methods from Japan, which could actually harm yields.

Bag cultivation of shiitake varies, first and foremost, based on whether the grower uses an “all-sides cultivation”, or a “top-only cultivation” system. Bag cultivation of shiitake in Japan is split roughly 60-40 between these two methods. In Japan, shiitake farms using “all-sides cultivation” where, after browning, the substrate block is removed from the bag, typically do a second flush. Very few cultivators only do one flush, as is typical abroad, and it is common to do a third flush. Likewise, in top-only cultivation, where only the top of the filter bag is cut off, the grower may use a single substrate block for an entire year, harvesting between 5~10 flushes from it. Therefore, in order to consider growing practices (including sawdust/wood chip fineness, wood varieties, supplementation and so on), there are three major variables to account for: the shiitake strain being used, the cultivation method, and how many flushes the grower aims to get. Aspects like quality and size of shiitake also matter a lot in Japan, where there are 12 size groupings for shiitake, along with the degree to which the cap has opened, and where prices vary considerably between grades. Shiitake growers in Japan, for instance, have to leave the stems intact on fresh Shiitake, which lose most value if the cap opens, and pre-cut shiitake is not a fresh market option. Japanese consumers are particular about blemishes, cap coloration, poor shape, and freshness (including any discoloration under the cap), making for the toughest and most discerning consumer base in the global market. Thus, a lot of Japanese industrial practice is based on appealing to such a consumer base.

Shiitake cultivation in Japan also uses a much wider variety of sawdust. The sawdust used for cultivation in Japan comes from lumber companies that cater to mushroom cultivation. The sawdust providers offer a range of particle sizes, wood mixtures, can regulate level of fermentation to an extent, and in some cases, can premix the supplements. Best practice outside of Japan would be to seek out long-term contracts with sawdust providers that can tailor their process to mushroom cultivation needs. Doing so both reduces running costs and also allows growers more room for experimentation, and enables more customized mushroom cultivation_emdash_especially important given that the conditions and needs of each operation and strain are quite different. This process is superior to trying to make do with a one-size-fits-all commercial sawdust, which is often too coarse or dry or old and otherwise poorly suited to the demands of mushroom cultivation. As the global exotic mushroom market grows, it should eventually reach a scale that enables the development of specialized infrastructure like sawdust providers. Such infrastructure is critical to lowering costs and establishing stable domestic production of exotic mushrooms.

However, sawdust in mushroom cultivation is, at the end of the day, not alchemy, though to a grower, it often feels like it. Getting a good yield does not require one to cut down a tree under a full moon and ferment it under a crow’s nest for two weeks before purifying the resulting sawdust by burning sage. Having toured several large-scale shiitake growers in Japan to research this topic, the difference between what they do and the official line pushed by researchers and spawn makers is, predictably, big. Even using just one species of tree for sawdust is logistically challenging and sometimes not feasible at all for a company going through 40~50 tons or more of sawdust a week. As with all industries, there is a gap between the laboratory “best practice” preached by the prophets in white coats and clean rooms, and the “best practice” possible for big businesses with a never-ending list of problems and things to do.
Big producers almost universally mix several sawdust varieties together, and those proportions are based first on cost and then on trial and error to get the best yield at the lowest cost. Very large growers often use a mixed oak tree sawdust. Even though beech trees also work well, beech sawdust is simply too expensive to be practical. One grower used two varieties of sawdust at a roughly 50-50 ratio. One was of oak trees, while the other was simply a blend of “deciduous trees”. What many large growers quickly find is that shiitake grow pretty well on a wide variety of sawdust medium provided they properly apply spawn and run a clean ship with well-regulated incubation rooms. In such a tight industry, shiitake growers in Japan make compromises where necessary, which often means taking a 10% reduction in yield for a 20% reduction in growing costs and those types of business decisions are going to vary between countries and even regions, as sawdust costs and wood varieties can vary in price considerably, as can with energy and labor. The standard production goal in Japan tends to be 1-kilogram of shiitake harvested from each 2.5-kilogram substrate block, for a bioefficiency of around 40%, which is not usually attained, because Japanese growers normally prune the initial pinning in order to maximize the number of large and quality shiitake they can harvest from each block, as there is, again, substantial market pressure in Japan for size and quality. Shiitake growers who are only doing one flush, can reasonably aim for 500~600 grams per 2.5-kilogram substrate block, and getting 700 grams is feasible if not pruning for size. Japanese shiitake farms typically harvest between 400~600 grams per substrate block in the first flush, depending on the extent of pruning.

The large shiitake grower mentioned previously was not simply tossing two mixes of sawdust together and calling it a day. They had a process obviously based on trial and error. The oak sawdust was rougher and they fermented it for between 7~10 days while the deciduous tree sawdust was much finer and not fermented prior to use. These are the kinds of micro-adjustments that each grower has to gradually work through to find what works best for their operation. That grower though, also told me that they found making minute tweaks to the incubation settings (length of incubation, temperature, higher carbon dioxide concentrations, not so much with humidity) had as big or bigger an impact on yield than sawdust alone did. Experimenting with slightly higher incubation temperatures allowed them to reduce the incubation time by a few days and increased the size of their first flush by a small margin. As the industry standard in Japan is to harvest through the third flush, there is less investment in research and testing on how to absolutely maximize yield from just the first (and by far the most efficient), flush. The Japanese industry, though, is also changing, with low prices increasingly pushing shiitake growers to cut costs and speed up the growing process. As a result, top-only shiitake cultivation and log cultivation are being steadily squeezed out, as both require far higher labor costs. The steady downward trend of mushroom prices for the past 15 years, is gradually forcing farms to abandon labor-intensive growing processes and reevaluate their methodologies.

Some Lessons from the Japanese Model
Japanese shiitake growers don’t toss inoculated substrate bags into mixers or shake them up by hand. Not only is this step completely unnecessary to shiitake cultivation, it can damage the bags, especially given the rougher particles of commercial sawdust used in other countries, and leads to breaks/punctures and more contamination in the incubation process. To describe the reaction of some Japanese shiitake spawn makers watching a video of this common step in shiitake cultivation abroad: they all literally groaned before visibly shaking their heads. A large shiitake company’s president laughed at the sight of it. Apart from the unnecessary labor and increased loss, this step can also damage or weaken the mycelia in the spawn, and does little to reduce incubation time that strain selection and incubation room climate regulation can’t already do. Forcibly trying too hard to decrease the incubation time also tends to reduce yields and the quality of the harvested mushrooms. Japan doesn’t shake spawn into bags or premix spawn into huge batches of sawdust, and yet manages to get premium yields of quality shiitake, despite the high energy and raw material costs.

Japanese shiitake growers manage to make a profit despite wholesale market prices having fallen to 8.56USD/kg (3.88/lb.) last year, though prices have recovered slightly 2022. A key part of their profitability is extremely low levels of contamination and failed spawn. An observer can walk through a large warehouse with over 10,000 incubated filter bags and almost be able to count the number of failed or contaminated substrate blocks on one hand. The reason why is because after the cultivation bags have been filled and the tops folded, they are loaded up on trays and put on trolleys, before being sterilized in a pressurized autoclave chamber. After a one-to-two-day cooling period, workers then transfer the sterilized substrate to a carefully maintained, negative pressure clean room, and use an automatic inoculation machine to ensure a fixed amount of spawn is evenly distributed to each block, typically between 10-15 grams for 2.5kg of substrate. Immediately after the spawn has been added to the substrate, the bags are folded shut again and moved to incubation rooms. At a Japanese shiitake farm, every employee works rapidly and efficiently, and every step of the process that can be automated, from sawdust mixers to inoculation machines, is mechanized. Even the shiitake sorting is automated! As previously mentioned, in Japan growers must sort fresh shiitake into 12 (or more) size categories for sale (oddly shaped shiitake, or shiitake whose caps have opened too much, are labeled as “defective” and can still be sold for very low prices, but still have to be sorted into small or large), but growers have also mechanized this process, with an easy-to-use but complex machine that includes laser sensors and scales, measuring shiitake that workers load onto the moving conveyer belt of trays at breakneck speed, and then automatically dumping those shiitake in the corresponding container box for their size.

The big secret to Japanese shiitake production: how the industry produces such large quantities of quality shiitake and manages to make a profit on it in a tight market has nothing to do with sawdust or supplementation and everything to do with one thing: automation. The profitability of the industry is not that Japanese growers are getting radically larger yields from some special sawdust mix or supplementation, it is, as is the case with Japanese industry more generally, a mixture of automation, and being well-grounded in the basics. Japanese industry, any industry, approaches its field with intense focus and care to the basics, down to every minutia and detail, no matter how seemingly unimportant or minimal the impact of that detail is to the whole. In the case of mushrooms, this means a focus on good reliable spawn and clean, consistent spawning with minimal losses and remarkably consistent yields throughout the year. Even though labor costs in Japan are low and most farms pay between 6.50~7.30 USD/hour depending on the conversion rate (another comparison is that the average labor costs are roughly 7.00 Euros an hour for full-time workers), taking into account that energy costs are much higher in Japan, as are raw materials (spawn alone is 3~4 times as expensive), the fact that Japanese shiitake farms can produce around 70,000 tons of fresh shiitake (this figure does not include the portion of shiitake produced for the dry market), a year at wholesale market prices of 8.56USD/kg, and still be a profitable enterprise (narrow as the margins may be), should serve as a testament for the efficiency of the Japanese model. Likewise, if prices continue to decline, the shiitake industry in Japan is likely to enter a period of rapid change, and the Japanese Exotic Mushroom Journal will continue to report the ongoing cost-saving measures being adopted by the industry, alongside continuing research into shiitake cultivation.

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Rethinking Shiitake

Looking at Cultivation in Japan