Cultivating King Oyster Mushrooms: Pleurotus eryngii

Cultivation of the King Oyster Mushroom has expanded rapidly in South East Asia over the past decade. From 1993, growing numbers of companies in China, Taiwan and Japan have begun commercially producing this tasty oyster mushroom. The King Oyster Mushroom is sold fresh on local markets and exported dried or in jars. This mushroom can be found in dried form in Chinese specialty stores. This article reports on ten years of research into this variety in Taiwan and China, and the cultivation techniques.

By Peter Oei, ECO Consult

The King Oyster Mushroom fully justifies its name: it is by far the most flavoursome of the oyster mushrooms. The thick, firm stems have a pleasant texture and a slightly sweet taste. Another plus point is its long storage life compared to other oyster mushroom varieties. This variety can easily be transported over long distances. It has also recently become known that this variety, just like the shii-take, lowers cholesterol levels. An excellent selling point in cultures where cardio-vascular diseases are major killers. 

The refined flavour has lead to a considerable price difference with the fungi usually cultivated in the Far East, the shii-take. The price of Pleurotus eryngii is about double that of shii-take in China; little surprise that cultivation is becoming more widespread.

Rare in nature

The King Oyster Mushroom's official name is Pleurotus eryngii:. The name eryngii indicates where the mushroom can be found in the wild: on the roots of umbelliferous plants, particularly Eryngium and Heracleum. It grows as a parasite on these plants - a big difference with the winter oyster mushroom, for example, which grows well on dead hardwood. This variety is extremely rare but it has been identified growing wild in various parts of the world- in North Africa, Central Asia and in the southern regions of the former USSR.

Low yields on straw

The usual methods of cultivating oyster mushrooms on straw give a low yield with King Oyster Mushrooms: from 8 to 12% of the substrate weight. In addition, infections repeatedly occur on pasteurised substrate. The reason is that King Oyster Mushrooms have a different metabolism to other oyster mushrooms. They are less able to decompose lignin so give a higher yield with more easily decomposable forms. But mixing this with pasteurised substrate increases the risk of competitor moulds. This variety is a far slower grower than the winter oyster mushroom or the pink oyster mushroom. This also increases the risk of infection, as it takes longer to fully colonise the substrate. Hygienic working practice is even more essential with this variety.

Growing on sterile substrate

Wood-loving strains that are difficult to cultivate on pasteurised substrate can be grown well on sterilised substrate. This applies to both the Velvet Foot or Enokitake and the King Oyster Mushroom. The substrate should be placed in a container resistant to high temperatures; the mycelium must have enough space to breathe at a later stage. The most commonly used containers are plastic bags (in China) and bottles (in Taiwan and Japan).

Depending on labour costs, the process is more or less automated. Special machinery is available which mixes the substrate, adds water, fills the bottles, makes a hole in the substrate and inserts a plug that allows air though. A 1100 millilitre bottle usually contains about 650 grams of substrate. The bottles are sterilised in man-high autoclaves. A special machine then automatically inoculates the bottles with spawn. The stacked crates then spend about 6 weeks in an incubation room.

Scratching

The next phase can be compared to ruffling casing soil in white cap mushroom cultivation. The mycelium at the top of the bottle is not all the same age; older spawn can cause abnormalities, so a machine 'scratches' away a small part of the upper substrate layer after incubation.

Research carried out in 2002 at the famous Pudong Mushroom Institute in Shanghai confirmed the importance of scratching. Although this treatment slightly reduces the number of fruit bodies (from on average 7.1 to 6.3), the scratched bottles have a better yield and quality.

Harvesting takes place three weeks later.

The cultivation stages

• Day 1. Mix sawdust with 40 % (volume) rice bran, moisten, fill in bottles with lid, sterilise within 6 hours, allow to cool to maximum 30 degrees Celsius.

• Day 2.   Inoculate with spawn in sterile area.

• Day 3 – 40.  Incubate at a temperature of 18.5 – 20.5 degrees Celsius.

• Day 41.  Scratch.

• Day 42 – 52.  Primordia formation, 8 hours per day 250 lux, RH: 85-95 %.

• Day 61 – 65. Harvest, grading, packing, cooling and distribution to auction or wholesaler.

Number of perforations per bag

The number of holes or perforations in the container growing King Oyster Mushrooms has a big influence on the yield. An experiment by dr. Peng, TARI* in 1996 showed that with plastic bags containing 1.2 kilos of substrate, closed by a plug, too few holes gave a lower yield. Bags where only the plug was removed, gave an average yield of 8.4%. Bags slit open at the bottom, then laid horizontally, gave an average yield of 12.8%.

New strains

Around 15 years ago I exchanged a large number of strains between China, Taiwan and a Belgian spawn producer. These strains included a Pleurotus eryngii strain, used in Taiwan for classic selection to develop commercially interesting strains. Unlike common mushrooms, the King Oyster Mushroom  is tetrapolar: this means there are four spores per basidium, that can be used as the base for one spore culture.

A report written by dr. Peng and others in 2001 describes how they combined the required characteristics from two strains (Holland 150 and ATCC 36047). Holland 150, a strain from the former Mycoblanc (taken over in the meantime by Mycelia), gave the highest yield, but a shorter storage life and relatively thin cap. This variety also quickly developed black blotches at high relative humidity. ATCC 36047 had attractive mushrooms with a firm stem and long storage potential.

Peng managed to develop four hybrid strains that reacted differently to changes to the substrate. The optimal substrate composition therefore depends on the strain. One of these strains will shortly be patented.

In China, strain selection is often accomplished by radiating the mycelium. This damages the DNA, which can create mutants. The majority of these mutants have worse traits than the original strain, but the law of averages rules here too. A small number of mutants have excellent production traits and are eventually introduced onto the market as commercial strains.

Optimal substrate composition

Peng and others have done various research studies into the optimal substrate composition. In trials, Holland 150 appeared to give the highest yield with 38 % rice bran, while the yield decreased at 48% rice bran.

Strain ATCC 36047, in contrast, produced more mushrooms as the percentage of rice bran rose.

Other studies aimed at discovering which supplement (in a 50% ratio) gave the highest yield with strain ATCC 36047: rice bran, wheat bran or maize flour. Wheat bran scored highest here for mushroom quality, but maize flour produced the highest yield.

The percentage of supplement is high compared to other exotic fungi, which can be explained by he parasitic nature of this variety. Anyone wanting to attempt cultivating this mushroom, first has to determine the optimal substrate mix for the chosen variety.

Prospects for Europe

In the Netherlands there are only a very small number of King Oyster Mushroom growers. Production of some significance is found in Spain (Micelios Fungisem) and Germany (Pilzfarm Helvesiek), while in the Netherlands Bert Rademakers of Fungi 2000 produces suitable substrate on a small-scale. The superb taste and long storage life give the King Oyster Mushroom a head start. To achieve greater market volumes, the price will have to drop a little. This can only happen if the yields rise and become more stabilised.