Six Step to Mushroom Farming
Posted by Unknown in Manure and Composting, Mushroom on Sunday 27 January 2013
Mushroom
farming consists of six steps, and although the divisions are somewhat
arbitrary, these steps identify what is needed to form a production
system.
The
six steps are Phase I composting, Phase II composting, spawning,
casing, pinning, and cropping. These steps are described in their
naturally occurring sequence, emphasizing the salient features within
each step. Compost provides nutrients needed for mushrooms to grow. Two
types of material are generally used for mushroom compost, the most used
and least expensive being wheat straw-bedded horse manure. Synthetic
compost is usually made from hay and crushed corncobs, although the term
often refers to any mushroom compost where the prime ingredient is not
horse manure. Both types of compost require the addition of nitrogen
supplements and a conditioning agent, gypsum.
The
preparation of compost occurs in two steps referred to as Phase I and
Phase II composting. The discussion of compost preparation and mushroom
production begins with Phase I composting.
Phase I: Making Mushroom Compost
This
phase of compost preparation usually occurs outdoors although an
enclosed building or a structure with a roof over it may be used. A
concrete slab, referred to as a wharf, is required for composting. In
addition, a compost turner to aerate and water the ingredients, and a
tractor-loader to move the ingredients to the turner is needed. In
earlier days piles were turned by hand using pitchforks, which is still
an alternative to mechanized equipment, but it is labor intensive and
physically demanding.
Phase
I composting is initiated by mixing and wetting the ingredients as they
are stacked in a rectangular pile with tight sides and a loose center.
Normally, the bulk ingredients are put through a compost turner. Water
is sprayed onto the horse manure or synthetic compost as these materials
move through the turner. Nitrogen supplements and gypsum are spread
over the top of the bulk ingredients and are thoroughly mixed by the
turner. Once the pile is wetted and formed, aerobic fermentation
(composting) commences as a result of the growth and reproduction of
microorganisms, which occur naturally in the bulk ingredients. Heat,
ammonia, and carbon dioxide are released as by-products during this
process. Compost activators, other than those mentioned, are not needed,
although some organic farming books stress the need for an “activator.”
Mushroom
compost develops as the chemical nature of the raw ingredients is
converted by the activity of microorganisms, heat, and some
heat-releasing chemical reactions. These events result in a food source
most suited for the growth of the mushroom to the exclusion of other
fungi and bacteria. There must be adequate moisture, oxygen, nitrogen,
and carbohydrates present throughout the process, or else the process
will stop. This is why water and supplements are added periodically, and
the compost pile is aerated as it moves through the turner.
Gypsum
is added to minimize the greasiness compost normally tends to have.
Gypsum increases the flocculation of certain chemicals in the compost,
and they adhere to straw or hay rather than filling the pores (holes)
between the straws. A side benefit of this phenomenon is that air can
permeate the pile more readily, and air is essential to the composting
process. The exclusion of air results in an airless (anaerobic)
environment in which deleterious chemical compounds are formed which
detract from the selectivity of mushroom compost for growing mushrooms.
Gypsum is added at the outset of composting at 40 lbs. per ton of dry
ingredients.
Nitrogen
supplements in general use today include brewerâs grain, seed meals of
soybeans, peanuts, or cotton, and chicken manure, among others. The
purpose of these supplements is to increase the nitrogen content to 1.5
percent for horse manure or 1.7 percent for synthetic, both computed on a
dry weight basis. Synthetic compost requires the addition of ammonium
nitrate or urea at the outset of composting to provide the compost
microflora with a readily available form of nitrogen for their growth
and reproduction.
Corn
cobs are sometimes unavailable or available at a price considered to be
excessive. Substitutes for or complements to corn cobs include shredded
hardwood bark, cottonseed hulls, neutralized grape pomace, and cocoa
bean hulls. Management of a compost pile containing any one of these
materials is unique in the requirements for watering and the interval
between turning.
The
initial compost pile should be 5 to 6 feet wide, 5 to 6 feet high, and
as long as necessary. A two-sided box can be used to form the pile
(rick), although some turners are equipped with a “ricker” so a box
isnât needed. The sides of the pile should be firm and dense, yet the
center must remain loose throughout Phase I composting. As the straw or
hay softens during composting, the materials become less rigid and
compactions can easily occur. If the materials become too compact, air
cannot move through the pile and an anaerobic environment will develop.
Turning
and watering are done at approximately 2-day intervals, but not unless
the pile is hot (145° to 170°F). Turning provides the opportunity to
water, aerate, and mix the ingredients, as well as to relocate the straw
or hay from a cooler to a warmer area in the pile, outside versus
inside. Supplements are also added when the ricks are turned, but they
should be added early in the composting process. The number of turnings
and the time between turnings depends on the condition of the starting
material and the time necessary for the compost to heat to temperatures
above 145°F.
Water
addition is critical since too much will exclude oxygen by occupying
the pore space, and too little can limit the growth of bacteria and
fungi. As a general rule, water is added up to the point of leaching
when the pile is formed and at the time of first turning, and thereafter
either none or only a little is added for the duration of composting.
On the last turning before Phase II composting, water can be applied
generously so that when the compost is tightly squeezed, water drips
from it. There is a link between water, nutritive value, microbial
activity, and temperature, and because it is a chain, when one condition
is limiting for one factor, the whole chain will cease to function.
Biologists see this phenomenon repeatedly and have termed it the Law of
Limiting Factors.
Phase
I composting lasts from 7 to 14 days, depending on the nature of the
material at the start and its characteristics at each turn. There is a
strong ammonia odor associated with composting, which is usually
complemented by a sweet, moldy smell. When compost temperatures are
155°F and higher, and ammonia is present, chemical changes occur which
result in a food rather exclusively used by the mushrooms. As a
by-product of the chemical changes, heat is released and the compost
temperatures increase. Temperatures in the compost can reach 170° to
180°F during the second and third turnings when a desirable level of
biological and chemical activity is occurring. At the end of Phase I the
compost should: a) have a chocolate brown color; b) have soft, pliable
straws, c) have a moisture content of from 68 to 74 percent; and d) have
a strong smell of ammonia. When the moisture, temperature, color, and
odor described have been reached, Phase I composting is completed.
Phase II: Finishing the Compost
There
are two major purposes to Phase II composting. Pasteurization is
necessary to kill any insects, nematodes, pest fungi, or other pests
that may be present in the compost. And second, it is necessary to
remove the ammonia which formed during Phase I composting. Ammonia at
the end of Phase II in a concentration higher than 0.07 percent is often
lethal to mushroom spawn growth, thus it must be removed; generally, a
person can smell ammonia when the concentration is above 0.10 percent.
Phase
II takes place in one of three places, depending on the type of
production system used. For the zoned system of growing, compost is
packed into wooden trays, the trays are stacked six to eight high, and
are moved into an environmentally controlled Phase II room. Thereafter,
the trays are moved to special rooms, each designed to provide the
optimum environment for each step of the mushroom growing process. With a
bed or shelf system, the compost is placed directly in the beds, which
are in the room used for all steps of the crop culture. The most
recently introduced system, the bulk system, is one in which the compost
is placed in a cement-block bin with a perforated floor and no cover on
top of the compost; this is a room specifically designed for Phase II
composting.
The
compost, whether placed in beds, trays, or bulk, should be filled
uniformly in depth and density or compression. Compost density should
allow for gas exchange, since ammonia and carbon dioxide will be
replaced by outside air.
Phase
II composting can be viewed as a controlled, temperature-dependent,
ecological process using air to maintain the compost in a temperature
range best suited for the de-ammonifying organisms to grow and
reproduce. The growth of these thermophilic (heat-loving) organisms
depends on the availability of usable carbohydrates and nitrogen, some
of the nitrogen in the form of ammonia.
Optimum
management for Phase II is difficult to define and most commercial
growers tend toward one of the two systems in general use today: high
temperature or low temperature.
A
high temperature Phase II system involves an initial pasteurization
period during which the compost and the air temperature are raised to at
least 145°F for 6 hours. This can be accomplished by heat generated
during the growth of naturally occurring microorganisms or by injecting
steam into the room where the compost has been placed, or both. After
pasteurization, the compost is re-conditioned by immediately lowering
the temperature to 140°F by flushing the room with fresh air.
Thereafter, the compost is allowed to cool gradually at a rate of
approximately 2° to 3°F each day until all the ammonia is dissipated.
This Phase II system requires approximately 10 to 14 days to complete.
In
the low temperature Phase II system the compost temperature is
initially increased to about 126°F with steam or by the heat released
via microbial growth, after which the air temperature is lowered so the
compost is in a temperature range of 125° to 130°F range. During the 4
to 5 days after pasteurization, the compost temperature may be lowered
by about 2°F a day until the ammonia is dissipated.
It
is important to remember the purposes of Phase II when trying to
determine the proper procedure and sequence to follow. One purpose is to
remove unwanted ammonia. To this end the temperature range from 125° to
130°F is most efficient since de-ammonifying organisms grow well in
this temperature range. A second purpose of Phase II is to remove any
pests present in the compost by use of a pasteurization sequence.
At
the end of Phase II the compost temperature must be lowered to
approximately 75° to 80°F before spawning (planting) can begin. The
nitrogen content of the compost should be 2.0 to 2.4 percent, and the
moisture content between 68 and 72 percent. Also, at the end of Phase II
it is desirable to have 5 to 7 lbs. of dry compost per square foot of
bed or tray surface to obtain profitable mushroom yields. It is
important to have both the compost and the compost temperatures uniform
during the Phase II process since it is desirable to have as homogenous a
material as possible.
Phase III: Spawning
Mushroom
compost must be inoculated with mushroom spawn (Latin expandere = to
spread out) if one expects mushrooms to grow. The mushroom itself is the
fruit of a plant as tomatoes are of tomato plants. Within the tomato
one finds seeds, and these are used to start the next season’s crop.
Microscopic spores form within a mushroom cap, but their small size
precludes handling them like seeds. As the tomato comes from a plant
with roots, stems, and leaves, the mushroom arises from thin,
thread-like cells called mycelium. Fungus mycelium is the white,
thread-like plant often seen on rotting wood or moldy bread. Mycelium
can be propagated vegetatively, like separating daffodil bulbs and
getting more daffodil plants. Specialized facilities are required to
propagate mycelium, so the mushroom mycelium does not get mixed with the
mycelium of other fungi. Mycelium propagated vegetatively is known as
spawn, and commercial mushroom farmers purchase spawn from any of about a
dozen spawn companies.
Spawn
makers start the spawn-making process by sterilizing a mixture of rye
grain plus water and chalk; wheat, millet, and other small grain may be
substituted for rye. Sterilized horse manure formed into blocks was used
as the growth medium for spawn up to about 1940, and this was called
block or brick spawn, or manure spawn; such spawn is uncommon now. Once
sterilized grain has a bit of mycelium added to it, the grain and
mycelium is shaken 3 times at 4-day intervals over a 14-day period of
active mycelial growth. Once the grain is colonized by the mycelium, the
product is called spawn. Spawn can be refrigerated for a few months, so
spawn is made in advance of a farmerâs order for spawn.
In
the United States, mushroom growers have a choice of four major
mushroom cultivars: a) Smooth white – cap smooth, cap and stalk white;
b) Off-white – cap scaly with stalk and cap white; c) Cream – cap smooth
to scaly with stalk white and cap white to cream; and d) Brown – cap
smooth, cap chocolate brown with a white stalk. Within each of the four
major groups, there are various isolates, so a grower may have a choice
of up to eight smooth white strains. The isolates vary in flavor,
texture, and cultural requirements, but they are all mushrooms.
Generally, white and off-white cultivars are used for processed foods
like soups and sauces, but all isolates are good eating as fresh
mushrooms.
Spawn
is distributed on the compost and then thoroughly mixed into the
compost. For years this was done by hand, broadcasting the spawn over
the surface of the compost and ruffling it in with a small rake-like
tool. In recent years, however, for the bed system, spawn is mixed into
the compost by a special spawning machine which mixes the compost and
spawn with tines or small finger-like devices. In a tray or batch
system, spawn is mixed into the compost as it moves along a conveyer
belt or while falling from a conveyor into a tray. The spawning rate is
expressed as a unit or quart per so many square feet of bed surface; 1
unit per 10 ft is desirable. The rate is sometimes expressed on the
basis of spawn weight versus compost weight; a 2 percent spawning rate
is desirable.
Once
the spawn has been mixed throughout the compost and the compost worked
so the surface is level, the compost temperature is maintained at 75°F
and the relative humidity is kept high to minimize drying of the compost
surface or the spawn. Under these conditions the spawn will grow –
producing a thread-like network of mycelium throughout the compost. The
mycelium grows in all directions from a spawn grain, and eventually the
mycelium from the different spawn grains fuse together, making a spawned
bed of compost one biological entity. The spawn appears as a white to
blue-white mass throughout the compost after fusion has occurred. As the
spawn grows it generates heat, and if the compost temperature increases
to above 80° to 85°F, depending on the cultivar, the heat may kill or
damage the mycelium and eliminate the possibility of maximum crop
productivity and/or mushroom quality. At temperatures below 74°F, spawn
growth is slowed and the time interval between spawning and harvesting
is extended.
The
time needed for spawn to colonize the compost depends on the spawning
rate and its distribution, the compost moisture and temperature, and the
nature or quality of the compost. A complete spawn run usually requires
14 to 21 days. Once the compost is fully grown with spawn, the next
step in production is at hand.
Phase IV: Casing
Casing
is a top-dressing applied to the spawn-run compost on which the
mushrooms eventually form. Clay-loam field soil, a mixture of peat moss
with ground limestone, or reclaimed weathered, spent compost can be used
as casing. Casing does not need nutrients since casing act as a water
reservoir and a place where rhizomorphs form. Rhizomorphs look like
thick strings and form when the very fine mycelium fuses together.
Mushroom initials, primordia, or pins form on the rhizomorphs, so
without rhizomorphs there will be no mushrooms. Casing should be
pasteurized to eliminate any insects and pathogens it may be carrying.
Also, it is important that the casing be distributed so the depth is
uniform over the surface of the compost. Such uniformity allows the
spawn to move into and through the casing at the same rate and,
ultimately, for mushrooms to develop at the same time. Casing should be
able to hold moisture since moisture is essential for the development of
a firm mushroom.
Managing
the crop after casing requires that the compost temperature be kept at
around 75°F for up to 5 days after casing, and the relative humidity
should be high. Thereafter, the compost temperature should be lowered
about 2°F each day until small mushroom initials (pins) have formed.
Throughout the period following casing, water must be applied
intermittently to raise the moisture level to field capacity before the
mushroom pins form. Knowing when, how, and how much water to apply to
casing is an “art form” which readily separates experienced growers from
beginners.
Phase V: Pinning
Mushroom
initials develop after rhizomorphs have formed in the casing. The
initials are extremely small but can be seen as outgrowths on a
rhizomorph. Once an initial quadruples in size, the structure is a pin.
Pins continue to expand and grow larger through the button stage, and
ultimately a button enlarges to a mushroom. Harvestable mushrooms appear
18 to 21 days after casing. Pins develop when the carbon dioxide
content of room air is lowered to 0.08 percent or lower, depending on
the cultivar, by introducing fresh air into the growing room. Outside
air has a carbon dioxide content of about 0.04 percent.
The
timing of fresh air introduction is very important and is something
learned only through experience. Generally, it is best to ventilate as
little as possible until the mycelium has begun to show at the surface
of the casing, and to stop watering at the time when pin initials are
forming. If the carbon dioxide is lowered too early by airing too soon,
the mycelium stops growing through the casing and mushroom initials form
below the surface of the casing. As such mushrooms continue to grow,
they push through the casing and are dirty at harvest time. Too little
moisture can also result in mushrooms forming below the surface of the
casing. Pinning affects both the potential yield and quality of a crop
and is a significant step in the production cycle.
Phase VI: Cropping
The
terms flush, break, or bloom are names given to the repeating 3- to
5-day harvest periods during the cropping cycle; these are followed by a
few days when no mushrooms are available to harvest. This cycle repeats
itself in a rhythmic fashion, and harvesting can go on as long as
mushrooms continue to mature. Most mushroom farmers harvest for 35 to 42
days, although some harvest a crop for 60 days, and harvest can go on
for as long as 150 days.
Air
temperature during cropping should be held between 57° to 62°F for good
results. This temperature range not only favors mushroom growth, but
cooler temperatures can lengthen the life cycles of both disease
pathogens and insects pests. It may seem odd that there are pests which
can damage mushrooms, but no crop is grown that does not have to compete
with other organisms. Mushroom pests can cause total crop failures, and
often the deciding factor on how long to harvest a crop is based on the
level of pest infestation. These pathogens and insects can be
controlled by cultural practices coupled with the use of pesticides, but
it is most desirable to exclude these organisms from the growing rooms.
The
relative humidity in the growing rooms should be high enough to
minimize the drying of casing but not so high as to cause the cap
surfaces of developing mushrooms to be clammy or sticky. Water is
applied to the casing so water stress does not hinder the developing
mushrooms; in commercial practice this means watering 2 to 3 times each
week. Each watering may consist of more or fewer gallons, depending on
the dryness of the casing, the cultivar being grown, and the stage of
development of the pins, buttons, or mushrooms. Most first-time growers
apply too much water and the surface of the casing seals; this is seen
as a loss of texture at the surface of the casing. Sealed casing
prevents the exchange of gases essential for mushroom pin formation. One
can estimate how much water to add after first break has been harvested
by realizing that 90 percent of the mushroom is water and a gallon of
water weight 8.3 lbs. If 100 lbs. of mushrooms were harvested, 90 lbs.
of water (11 gal.) were removed from the casing; and this is what must
be replaced before second break mushrooms develop.
Outside
air is used to control both the air and compost temperatures during the
harvest period. Outside air also displaces the carbon dioxide given off
by the growing mycelium. The more mycelial growth, the more carbon
dioxide produced, and since more growth occurs early in the crop, more
fresh air is needed during the first two breaks. The amount of fresh air
also depends on the growing mushrooms, the area of the producing
surface, the amount of compost in the growing room, and the condition or
composition of the fresh air being introduced. Experience seems to be
the best guide regarding the volume of air required, but there is a rule
of thumb: 0.3ft/hr when the compost is 8 inches deep, and of this
volume 50 to 100 percent must be outside air.
A
question frequently arises concerning the need for illumination while
the mushrooms grow. Mushrooms do not require light to grow, only green
plants require light for photosynthesis. Growing rooms can be
illuminated to facilitate harvesting or cropping practices, but it is
more common for workers or mushroom farmers to be furnished with minerâs
lamps rather than illuminating an entire room.
Ventilation
is essential for mushroom growing, and it is also necessary to control
humidity and temperature. Moisture can be added to the air by a cold
mist or by live steam, or simply by wetting the walls and floors.
Moisture can be removed from the growing room by: 1) admitting a greater
volume of outside air; 2) introducing drier air; 3) moving the same
amount of outside air and heating it to a higher temperature since
warmer air holds more moisture and thus lowers the relative humidity.
Temperature control in a mushroom growing room is no different from
temperature control in your home. Heat can originate from hot water
circulated through pipes mounted on the walls. Hot, forced air can be
blown through a ventilation duct, which is rather common at more
recently built mushroom farms. There are a few mushroom farms located in
limestone caves where the rock acts as both a heating and cooling
surface depending on the time of year. Caves of any sort are not
necessarily suited for mushroom growing, and abandoned coal mines have
too many intrinsic problems to be considered as viable sites for a
mushroom farm. Even limestone caves require extensive renovation and
improvement before they are suitable for mushroom growing, and only the
growing occurs in the cave with composting taking place above ground on a
wharf.
Mushrooms
are harvested in a 7- to 10-day cycle, but this may be longer or
shorter depending on the temperature, humidity, cultivar, and the stage
when they are picked. When mature mushrooms are picked, an inhibitor to
mushroom development is removed and the next flush moves toward
maturity. Mushrooms are normally picked at a time when the veil is not
too far extended. Consumers in North America want closed, tight,
mushrooms while in England and Australia open, flat mushrooms are
desired. The maturity of a mushroom is assessed by how far the veil is
stretched, and not by how large the mushroom is. Consequently, mature
mushrooms are both large and small, although farmers and consumers alike
prefer medium- to large-size mushrooms.
Picking
and packaging methods often vary from farm to farm. Freshly harvested
mushrooms must be kept refrigerated at 35° to 45°F. To prolong the shelf
life of mushrooms, it is important that mushrooms “breathe” after
harvest, so storage in a nonwaxed paper bag is preferred to a plastic
bag.
After
the last flush of mushrooms has been picked, the growing room should be
closed off and the room pasteurized with steam. This final
pasteurization is designed to destroy any pests which may be present in
the crop or the woodwork in the growing room, thus minimizing the
likelihood of infesting the next crop.
Conclusion
It
takes approximately 15 weeks to complete an entire production cycle,
from the start of composting to the final steaming off after harvesting
has ended. For this work a mushroom grower can expect anywhere from 0 to
4 lbs. per square foot; the national average for 1980 was 3.12 lbs. per
square foot. Final yield depends on how well a grower has monitored and
controlled the temperature, humidity, pests, and so on. All things
considered, the most important factors for good production appear to be
experience plus an intuitive feel for the biological rhythms of the
commercial mushroom. The production system used to grow a crop can be
chosen after the basics of mushroom growing is understood.
Related Readings
- Atkins, Fred C. 1974. Guide to Mushroom Growing. Faber and Faber Ltd., 3 Queen Square, London.
- Blum, H. 1977. The Mushroom Industry in Ontario. Economic Branch, Ontario Ministry of Agriculture and Food, Toronto, Ontario.
- Chang, S.T. and W. A. Hayes. 1978. The Biology and Cultivation of Edible Mushrooms. Academic Press, New York.
- Lambert, L. F. 1958. Practical and Scientific Mushroom Culture. L. F. Lambert, Inc. Coatesville, PA 19230.
- Swayne, J. B. 1950. Handbook of Mushroom Culture, Kennett Square, PA 19348.
- Vedder, P. J. C. 1978. Modern Mushroom Growing. Pitman Press, Bath, G. B. Distributed in U.S.A. by S.A.S., Inc., RFD 1, Box 80 A, Madisonville, TX 77864.
The Pennsylvania State University,
College of Agriculture, Extension Service,
University Park, Pennsylvania
