Shiitake cultivation is slowly developing in Europe. A number of production techniques have been tried over the past few years, with varying degrees of success. The market has also increased slightly, but remains small. If new growers join the market, or a certain substrate gives higher yields than normal, there is a real risk of over production. It's only wise to consider growing shiitake if you already have a guaranteed market.

The tradition method of cultivating shiitake on logs is only sporadically seen in Europe. Log cultivation in China, Korea and Japan is also falling, whereas cultivation on substrate is rising fast. The huge advantage of log cultivation is the very low investment outlay: all that's really needed are the right type of logs (from the oak or shii tree in Japanese, Castanopsis cuspidata), spawn and a suitable location.

The spawn is placed in holes evenly spaced over the log. Over the past five years a trend has emerged which uses pre-colonised sawdust plugs instead of spawn on wooden dowels. This system can reduce the inoculation time by up to 30 to 50 %: from two years to 12 to 18 months. In South Germany growers use grain spawn which is inserted into larger holes spaced further apart; this grain spawn is more aggressive than sawdust, but more vulnerable to attack by insects and rodents.

The Dutch climate is less suited to traditional methods of outside cultivation on logs. Piercing winds and the relatively drier air means that good quality mushrooms can only be grown in sheltered spots and during periods of moist climatic conditions. However favourable yields can be achieved if the first stage of growth takes place outdoors, while pinheading is done in controlled conditions.

Balkbrug near Zwolle houses one of the largest shiitake growing facilities on logs in the Netherlands, Haveman Groen B.V. Current production is limited to 50 to 100 kilos per week but the traditional method of log cultivation and SKAL certification ( the inspection body for organic production in the Netherlands)  contribute to a higher price. Haveman are able to produce year-round thanks to the purchase of a large former, cold store with a simple floor heating system. The investments were low, but inoculating and soaking the logs is heavy, labour intensive work. The owner is considering mechanizing transport and soaking.

In Japan, growers stack the logs on pallets and attach the logs to an iron loop. This holds the logs in place during soaking. The entire pallet is soaked, then moved to a cultivation room. The labour costs in the Netherlands mean a higher level of mechanization is needed to achieve any reasonable profits. In addition, this method of cultivation is limited by the availability of suitable, good quality oak logs. In certain areas good oak is in short supply.

Substrate cultivation

Europe shiitakes are mainly grown on substrate. This is an area where the greatest developments have taken place in recent years. There are three different substrate preparation techniques: sterilization after filling, bulk sterilization and dry sterilization (table).

The majority of growers use the first cultivation method. Labour can be reduced using an autoclave with double doors, so the bags only have to be folded closed for sterilization. With single-door autoclaves the bags have to be heat-sealed for sterilization to prevent infection when the autoclave is opened. In the West, the major substrate companies are switching over to bulk sterilization processes. This is more economical if more than 10 tons of substrate is produced weekly.       

Sterilization after filling

1 Humidifying and mixing substrate

2 Bagging

3 Sterilization in autoclave

4 Inoculation    

This is still the most popular technique. However, filling the bags, then inoculating (after sterilization and cool down) per bag is relatively labour intensive. Inoculation must take place under sterile conditions, for example under a laminar flow system. The amount of spawn used varies from 1 to 5 %. This is a stable technique, which has provided good results over the past twenty years. If any diseases are discovered, the infected bag can be simply removed without the risk of contaminating the rest of the substrate.        

Bulk sterilization

1 Humidifying and mixing substrate

2 Sterilization in bulk mixer

3 Inoculation in bulk

4 Bagging        

A mixer is an expensive piece of equipment; to create sufficient capacity the substrate has to be cooled down very quickly (e.g. using glycol in the double jacket in the mixer). If inoculation itself is done in the mixer, there is a risk of infecting the entire batch; applying the spawn is a process requiring critical attention. Inoculation at filling is less risky. Sterile conditions are obviously essential here too. The amount of spawn used is 0.5 to 4 %.

Dry sterilization

1 Dry heat treatment

2 Humidifying and mixing substrate with 10 % (!) spawn

The simplest technique is to moisten special, pre-treated oak chips and blend them with copious amounts of spawn. The greatest advantage of this method is the almost total lack of investment involved (a cement mixer will do!). It's important to choose a mixer that doesn't breakdown the structure of the spawn. 10 % spawn is required, as the spawn isn't only used for inoculation but also as a nutrient medium. The disadvantage of this method is the high cost for the raw materials.

Substrate bags

The choice of bag depends on the relevant technique: with bulk sterilization the bags don't have to be made from heat-resistant polypropylene. Nowadays most companies that prepare substrate use bags with filters. A few exceptions, such as Schweinsberger Pilzzucht near Frankfurt, still use the Chinese method with foam plugs acting as a filter.

An important aspect here is correct air exchange. If the filter doesn't allow enough air through, the yield may be reduced by up to a half.

The substrate blocks used in Europe are usually larger than in the USA: in America the standard size is 3 kilos, while growers here prefer 4 to 5 kilos of substrate per bag. For years CTB (Cultuur Techniek Brabant) even delivered substrate in 15-kilo blocks. However, it took longer before all the flushes could be harvested.

Filling methods

The simplest filling method is an auger filler with a spout. The bags are held open manually and the quantity of substrate controlled by a foot-operated pedal. This is not the most creative occupation with large-scale production - plus it is highly labour intensive.

A completely new trend is the use of so-called Form, Fill & Seal (FFS)-machines. This type of machinery has been commonplace in the food sector for years, but has only been used in mushroom cultivation since quite recently. The smallest machines can make 8 to 10 substrate packages per minute, each containing around 3 kilos of substrate. This is the standard size in the United States and an ideal size for sterilization (the larger the substrate packages, the longer sterilization takes).

Better quality FFS-machines are nearly entirely made from stainless steel, which is easy to clean and complies with HACCP directives. They are also much safer than the bag filling machinery used in Taiwan and China. In those countries the bags have to be placed underneath the filling spout by hand, under circumstances where the many moving parts cause a great deal of occupational accidents.

FFS machines have few moving parts and operate fully automatically. The filled bags come off the machine onto a conveyor belt. Depending on the sterilization technique used to prepare the substrate, it will already have been sterilized (in bulk) or will be sterilized in the filled bags. An added advantage of this method is the lower cost of the substrate packaging which is around 40 to 50 % cheaper, as the machine forms and folds the bags using (inexpensive) rolls of polypropylene with filters.

Market

In Europe production aimed at the fresh market is essential; the prices for dried shiitake are so low it's impossible to compete with imported produce. The price for fresh shiitake has been somewhat under pressure the past few months resulting from increasing production from a remarkably productive type of substrate. There is also competition from imported mushrooms - including from Finland and China. In the United States, the import of low quality shiitake at rates below the North American cost price has forced many growers to switch over to ‘organic cultivation’ or growing a different type of exotic edible mushroom.

The yield from shii-take substrate remains variable; an annual average of 15 % is not uncommon - with exceptional production of 30 % also occurring.

Peter Oei is chairman of ECO Consult Foundation that promotes the use of mushrooms. Under the trade name Spore different mushroom products are distributed to the general public. ECO Consult also distributes special plastic bags for exotic mushroom growing and spawn in Europe. Peter is the main author of the recently published 3rd edition of ‘Mushroom Cultivation’, which is distributed by C point (www.cpoint.nl). For more information: www.spore.nl, e-mail: spore@antenna.nl.