Cover Image
close this book FOOD CHAIN No. 14 - March 1995
View the document GREETINGS
View the document A mouldy old business spawns some money
View the document Training for the Tropics
View the document Tomato concentrate - further developments from India
View the document Safety of street foods in Calcutta
View the document Quality of honey for export
View the document Improving standards of hygiene
View the document Book Lines
View the document Quality control and quality assurance
View the document Ghee - adding value to milk
View the document Acknowledgments

A mouldy old business spawns some money

In this second of three articles by Dr Peter Fellows, a mould (mushroom) is described to show how it can form the basis of a viable small business.

Mushrooms (or fungi) are a prized delicacy in most countries and form an integral part of meals throughout Asia and in many African and Latin American countries. They are also a rich source of protein, minerals and vitamins. There are many hundreds of different types that are edible, and many more hundreds of types that are inedible or even poisonous. The most common types that are specially cultivated include 'button' mushrooms, oak mushrooms, and straw mushrooms, although there are many other local varieties that are collected from forests for food or as medicines.

In countries where mushrooms are collected the seasonal supply and limited distribution make them highly valued and therefore very valuable. This is a good basis for an enterprise - but one that is able to operate for only a small part of the year. Mushroom cultivation is a new idea In many countries, but the value of the product and the relatively low investment make this a potentially profitable business idea.

WHAT IS NEEDED

To grow mushrooms as a business, a support material (or substrate) is needed to provide an anchorage for the growing mushrooms, to ensure good aeration and to provide correct water holding - neither too wet nor too dry - and to provide the necessary nutrients for the mushrooms to grow well. Different varieties will grow better on some substrates than on others (Table 1).

Equipment and materials are also needed to prepare the mushroom 'spawn' (these are small fragments of a network of threads known as a mycelium). Each type of mushroom must first grow from the spawn to form a new mycelium. The actual mushrooms can be thought of as fruits that then grow from the mycelium branches. Different varieties of mushroom need specific temperatures to grow into the mycelium and then to form fruit (Table 1) and they also respond differently to light (Table 1).

 

Table 1: Growth of four common mushroom varieties

Variety

Typical substrate

Temperature (°C)

Light

Growth, Fruiting

       

Button (or field) mushroom (Agaricus)

1) Spent brewers grains corn cobs, hay

30

25

no

 

2) Rice straw fertiliser, calcium carbonate species

     
 

3) Horse manure, brewers grains, gypsum

     

Straw mushroom (Volvariella species)

Used tea leaves, cotton waste, rice straw, coffee hulls, coir dust, sawdust mixed with corn meal. Each may be composted or un-composted and several substrates may be mixed

20-25

28-32

no

Oyster mushroom (Pleurotus species)

Cotton waste, rice straw, coir dust, sawdust mixed with corn meal. Each may be composted or un-composted

25 - 32

25

yes

Oak (or shiitake) mushroom (Lentinula species)

Logs of Leucaena species or other trees, sawdust compacted into polypropylene bags

22-27

15-20

For maturation only

In countries where mushroom cultivation is new it is common for the mushroom farmers to do each stage of production themselves. In areas where production is more established the different stages of production may be done by specialised businesses - involved in only one operation - such as prepares of substrate, or spawn makers who sell on to growers.

STARTER CULTURES

The first stage in production is to obtain - from a mushroom laboratory or commercial supplier - a pure starter culture of the variety to be grown. Many university departments or agricultural research stations in developing countries have mushroom laboratories. Different strains of each variety will vary in their yield, and technical advice from the supplier should be sought to select the best strain. The starter is then used to prepare spawn by growing it on a pasteurized substrate (the same as that used later to grow the mushrooms).

SUBSTRATES

Substrates for species including Volvariella and Pleurotus are usually based on agricultural residues such as chopped straw, sawdust, bagasse or corn cobs Rice bran (20 per cent) and 1 per cent lime may be added to adjust the acidity of the substrate. It is important that the source of substrate is close to the mushroom cultivation site to reduce costs.

A growing house made of thatch is suitable to control humidity and heat, and protect the beds from sunlight. If the growing beds are to be pasteurized a steam boiler is needed. After the beds have been prepared, steam is introduced into the growing house for about two hours until the air temperature has risen to 60-62°C. This is then maintained for another two hours and then lowered to 52°C and held at this temperature for a further eight hours. Finally the temperature is allowed to fall to about 35°C over the next 12 - 16 hours, and the bed is then ready for adding the spawn. This is added at 0.4 per cent (by weight) of the bed.

Unpasteurized substrate made from straw can be prepared by tying it into bundles, soaking overnight and piling into heaps of three or four layers with the spawn broadcast between the layers. The heap is then compacted to 30-60 cm thick. In another method, straw, cotton waste, and other substrates are soaked separately and then compacted in layers into 30 cm high x 30 cm wide x 100 cm long wooden frames, with spawn between the layers

The technology for sawdust substrates is different. Fresh sawdust is composted by soaking it and mixing with one per cent urea and one per cent lime, then storing it in a covered heap for 30-40 days, turning it every seven days. In a shorter method 78 per cent sawdust is mixed with 20 per cent rice bran, one per cent sugar and one per cent lime and composted for seven days. The compost is then compressed into blocks or into polypropylene bags. The substrate is steamed either at 100°C for 2-3 hours or at 60-70°C for 6-8 hours, cooled, and then spawn is added.

GROWTH

The spawn is allowed to grow into the full mycelium. This can take 10-15 days for volvariella species, 2-4 weeks for Pleurotus and Agaricus species and 2 - 3 months for Lentinula species depending on the climate.

After full development of the mycelium, when the mould has fully penetrated the substrate, the mushrooms begin to develop first as buttons and later as 'umbrellas' or 'flowers'. Agaricus and Volvariella are picked as buttons, the others as flowers. Mushrooms should be picked and not cut to prevent infection of the mycelium.

If the mushrooms are kept cool they will stay fresh for about one week. If they are not sold fresh, the main method of preservation is by drying.

POTENTIAL PROBLEMS

The most common problem is contamination of the spawn or substrate by other micro-organisms or low yielding strains. This can be overcome by ensuring spawn comes from a competent supplier and that the substrate is pasteurized. Some growers do not pasteurise the substrate because of the higher costs While this may be possible for substrates which have a low risk of contamination - e.g. cotton waste - it is not generally to be recommended.