High Moisture Grain
Michael T. Talbot
Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida, Gainesville
John T. Woeste, Dean for Extension
OCT 13 1986
I.F.A.S. Univ. of Florida
High Moisture Grain Storage
Michael T. Talbot
Michael T. Talbot is an Extension Agricultural Engineer in the
Agricultural Engineering Department, University of Florida.
For centuries the main method, if not the only method, for prevent-
ing mold growth and deterioration in stored grain was storing it at
moisture contents too low for molds or fungi to function. In starchy
cereal seeds moisture contents of 13.5 to 14.0% are high enough for
storage molds to slowly damage the grain. The higher the moisture con-
tent, the faster the spoilage. Keeping grain dry is still the principal tac-
tic in the fight against mold in grain. However, certain aspects of farm
technology in the past two decades have made low moisture content
a difficult and not always desirable goal.
The adoption of field shelling of corn, instead of picking and storing
ear corn, is the biggest single factor responsible for having to deal with
high moisture grain. Maximum yields for corn, as well as other grains,
are obtained by harvesting as soon as possible after the kernels have
reached their maximum dry weight. Thereafter, yields are pro-
gressively lower because of insects, fungi, birds, lodging, and weather.
The optimum yield stage, however, occurs when the grain is at a high
moisture content, often about 30 %. With modern equipment available
to rapidly harvest high moisture grain, principally corn and grain
sorghum, farmers bring from the fields an extremely perishable com-
modity. In mild or warm weather, high moisture corn may have con-
siderable microbial growth, and will begin heating and developing off-
odors within a few hours after harvest. Therefore, it is imperative that
appropriate grain conditioning procedures are begun immediately.
Though artificial drying is the number one means of conditioning
high moisture corn, it is not a completely satisfactory solution to every
corn-handling problem. The prospect of fuel shortages and higher fuel
costs plus the fact that most drying systems will not keep pace with
modern harvesting equipment, causing harvesting bottlenecks,
detract from the advantages of artificial drying. Systems which use less
fossil fuel energy are likely to become increasingly attractive.
It is rare to find a farmer who is not satisfied with high moisture grain
storage, often the easiest and best system. Grain with high moisture
content has been shown in feeding tests to be superior to dry grain in
feed efficiency, especially for beef cattle. This means fewer pounds
of grain are required to produce a pound of meat. Results are variable,
however, with beef cattle on high moisture grain showing increases in
efficiency from none to greater than 10 % over dry grain. An average
reported increase in efficiency was about 4 to 6%. Because of the in-
creased efficiency of high moisture grain, many farmers add water or
"reconstitute" dry grain before feeding. This, of course, adds extra
To take full advantage of early harvest and high moisture grain
feeding, farmers have looked for better ways to store wet grain. High
moisture grain can be stored by either of two methods. It can be ensil-
ed in storage or acid treated before being placed in storage. In either
case the kernel moisture of the grain should be relatively high. For en-
siled corn the moisture content (wet basis) should range from 25 to 30 %
with 28% being ideal. The outside limits are from 23 to 35% moisture
content. If corn is in the 18 to 23% moisture content range, it is very
difficult to store except in special storage structures. This is the range
where spontaneous combustion is likely to occur if the grain is not en-
siled, dried, or treated.
Preserving high moisture grains with chemicals has some unique ad-
vantages over other grain storing and handling methods. It also has
some drawbacks, which will be addressed below. Acid-treated grain
can be stored at a lower moisture content than ensiled grain. The range
for acid-treated grain is from 18 to 27% moisture content.
Another aspect of storing high moisture grain is the space required.
Wet grain takes more storage space than dry grain. For example, 30%
moisture content corn requires 1.41 cubic feet per bushel, and dry corn
at 15.5% moisture content requires 1.25 cubic feet per bushel. Only
about 88% as much high moisture shell corn can be stored in the same
volume as dry corn.
The principle behind the storage of high moisture grain is a low pH,
whether it is stored as ensiled grain or as acid-treated grain. Low pH
means that the acidity has been increased in the grain to prevent
growth of molds or certain microorganisms. By definition pH indicates
a measure of the acidity of a solution. The range in acidity is from a low
of 1 which is extremely acid to a high of 14 which is very basic or
alkaline. Pure water has a pH of 7 which is considered neutral.
Therefore, water is neither alkaline nor acid. The pH for high moisture
grain storage should range from about 3.8 to 5, preferably closer to 3.8.
A low pH in grains, as mentioned above, can be obtained by either of
two ways: (1) fermentation, which causes a low pH to occur natural-
ly in the stored grain, or (2) adding acid, which causes increased acidity
to occur artificially as the grain goes into storage.
The ensiling process is a method of obtaining fermentation which in
turn increases acidity. Essentially this occurs in three phases. The first
phase is marked by the reduction of respiration within the grain cells.
Respiration will continue until nearly all oxygen in the storage has been
used. In this process some grain carbohydrates are converted to car-
bon dioxide, water, and heat. As oxygen is depleted, microorganisms
become more active. A slight protein breakdown may occur as this first
phase of the fermentation process takes place. The first phase is
generally of very short duration, lasting only from as few as 5 hours to
as long as 2 days. The length of the first phase is governed by how well
oxygen is excluded from the structure.
The beginning of the second phase of the fermentation process oc-
curs when most of the oxygen has been used. Microorganisms requir-
ing oxygen cease activity in this phase. Other bacterial activity in-
creases which marks the beginning of fermentation. Carbohydrates,
sugars, and starches in the grain are converted to organic acids. The
pH of the grain drops as the acidity increases and this in turn reduces
microbial action and finally causes fermentation to decrease.
In the third phase the pH drops to around 4 or perhaps a little below
4. The lactic and acetic acids which have been generated in the fermen-
tation state tend to preserve the grain. The entire process takes about
3 weeks after which preservation can be indefinite if air and water are
excluded from the system. In the process about 4% of the food energy
may be lost as carbohydrates are converted to other products.
Fermentation has some added value in terms of feeding since grain
is partially predigested before it is consumed by animals. The value of
this predigestion is related to the type of animal which consumes the
grain. Primarily predigested grain is of value to ruminant-type animals.
It is worth from 8 to 15% more than dry grain for fattening cattle if it
has been ground, rolled, or cracked before ensiling. There appears to
be no advantage in terms of predigestion due to fermentation for grow-
ing and finishing hogs.
The remainder of this discussion will be presented in two parts: that
for ensiled high moisture corn, and that for artificial ensiling by the ad-
dition of acid. Corn is the primary crop in which high moisture is a pro-
blem. Grain sorghum, and to a lesser extent barley and oats, could also
Ensiling High Moisture Corn
High moisture corn should be ensiled when brought from the field
at a moisture content ranging from 25 to 30 %. If the moisture content
is below 25 %, water should be added to bring the moisture content up
to 25 % or more. The amount of water which may be added is limited
to about 2 percentage points. If the moisture content is 23 % or above,
then 2 % of moisture can be added to bring the corn up to 25% or more
for storage. The moisture content is brought up to the desired level by
spraying water on the corn as it is augered or elevated into storage at
the rate of about 2.5 gallons per ton for each percentage point to be
added. To increase the moisture content 2 percentage points, 5 gallons
of water need to be added to each ton or approximately 35 bushels.
Several considerations are important when ensiling high moisture
corn. The producer must determine if the type of storage which is
available or to be purchased is suitable for the storage of ensiled high
moisture corn. There are essentially two or possibly three major types
of storage systems available for the storage of high moisture corn. The
first are the conventional upright storage structures which include
concrete stave, poured concrete, and other types of silos typically used
for ensiling forage (Figure 1). Upright storage bins which are specifical-
ly designed for the storage of high moisture corn may also fit into this
A second type of storage system for high moisture corn is the limited
oxygen storage system (Figure 2). These units are specifically design-
ed to handle all types of high moisture grain and forage for feeding pur-
poses. These units are usually constructed of high quality materials
which retard corrosion and other difficulties associated with highly
acidic materials. Limited oxygen storage are generally glass lined or
epoxy coated to keep the acidity from coming into contact with the
metal part of the structure. Consequently, limited oxygen storage are
considered to be of high quality. Also, they generally cost more to pur-
chase and install.
A third type of storage system which may be considered for the
storage of high moisture corn is the horizontal silo (Figure 3). This may
be simply a trench or a bunker-type silo (Figure 4), or the commercially
available systems (Figure 5) which involve compaction of silage or high
moisture corn into large plastic bags (150-180 tons). The plastic bag (if
not damaged) is airtight. For the trench or bunker-type silo, provision
FIGURE I. CONVENTIONAL UPRIGHT SILO
FIGURE 2. SEALED STORAGE
must be made to prevent air from entering the silo. Generally, the open
silo is made airtight by installing a lining and covering the grain with
a tough plastic material which prevents the entrance of air. Horizon-
tal silos are a lower cost type (a rather large capital investment is re-
quired for the plastic bag compaction equipment) of storage for high
moisture grain but losses are usually higher and more feeding problems
may be associated with their use. Also, there is the possibility of
rodents or other animals walking on, breaking, or cutting openings in
the covering material or plastic bag which can cause spoilage to occur.
The type of silo used has little to do with the keeping quality of grain
after it is removed. The grain which has been ensiled should not be ex-
posed to air for any extended period of time. Generally, the grain
should be fed within 4 to 10 hours after it has been removed from the
silo. When unloading conventional silos at least 2 inches per day must
be removed from the top where it is exposed to air in cool weather.
When the weather warms, the removal rate may have to be increas-
ed to 3 to 4 inches per day to prevent excessive spoilage. In horizontal
silos the same general recommendations are made in that the open sur-
face should not be exposed to air for more than a few hours. For
horizontal silos up to about 4 inches per day per square foot of surface
area that is exposed to air must be removed in order to prevent
spoilage. This is somewhat more difficult to do when removing high
FIGURE 3. HORIZONTAL SILO
FIGURE 4. TRENCH SILO
moisture grain from a horizontal silo. For limited oxygen-type storage
there is a minimum amount of high moisture grain which must be
removed each day since the surface of the grain is not exposed to air.
A farmer may remove a few inches one day and then wait several days
before removing additional grain from this type of storage. Increased
versatility in feeding is permitted with this type of storage system.
In any case, whether the storage is conventional or limited oxygen,
the grain should not be allowed to stand in a feeder for any extended
period of time. Grain which is exposed to air for extended periods of
time tends to mold and create animal health problems which are dif-
ficult to treat medically. Only the amount of grain that will be eaten
in a given allowable time should be placed in the feeder since high
moisture grain spoils rapidly. The allowable time depends upon the
temperature of the surrounding air and consumption rate. Many pro-
ducers have experienced trouble feeding high moisture grain in self-
feeding livestock feeders.
Acid Treatment of Grain
When properly applied, acid-type grain preservatives kill and inhibit
development of the fungi (or molds) and related microorganisms in
grain, and continue almost indefinitely to prevent mold growth. The
embryo of the grain kernel is also killed, so there is essentially no
respiration or other biological activity. The mode of action is not
known for certain, although the process is often likened to preserving
foods in vinegar (a dilute acetic acid solution). Preservation is
associated at least partly with the low pH in treated grain, although
reduction of pH to similar levels using other kinds of acids does not pre-
vent mold growth.
The best mold inhibitors, considering efficiency, cost, and safety, are
propionic acid and closely related compounds. These include pro-
pionic, propionate and ammonium isobutyric acids, and a few salts
FIGURE 5. COMPACTED PLASTIC STORAGE BAG LOADING.
such as sodium propionate, potassium sorbate, and ammonium
isobutyrate. The salts are less effective compared with the acids. The
acids on the market are propionic alone or propionic mixed with one
of the other acids, primarily acetic. The choice of these acids is a mat-
ter of net cost of the treatment, and perhaps differences in cor-
rosiveness, odor, handling properties, and silage palatability.
Table 1. Propionic Acid Required for Preventing Mold Growth in High
Moisture Propionic acid required
content % Ib/ton oz/bushel
18 0.3-0.6 6-12 2.5-5
22 0.5-0.8 10-16 4.0-7
26 0.6-1.0 12-20 5.0-8
30 0.8-1.2 16-24 7.0-10
Application of the Acid
The amount of chemical required depends primarily on the mold in-
hibitor used and the grain moisture content, the wetter grain requir-
ing more preservative (Table 1). For each moisture level, a range of ap-
plication rates is given. The higher rates are considered safe for storage
up to a year and are similar to those recommended by most major sup-
pliers. The lower rates should be safe for shorter storage in cool
weathers, such as from fall harvest until early spring. The usual
method of applying liquid preservatives is to spray the grain as it moves
through an auger (Figure 6). Complete applicators, including auger,
pump, metering controls, and automatic safety shut-offs, are on the
market. A typical unit is illustrated in Figure 7. Most applicators have
a maximum capacity of about 1000 bushels per hour. After determin-
ing the grain moisture content and the rate of throughput of the auger,
FIGURE 6. HANDLING GRAIN FOR EFFECTIVE PRESERVATIVE TREATMENT
FIGURE 7. SKETCH OF TYPICAL APPLICATOR FOR LIQUID
the meter is set for the desired level of application. Throughput will
vary with type of grain and its moisture level. Proper application is
essential; applying too much acid raises the treatment cost, and too lit-
tle may result in spoilage. It is especially important that no appreciable
quantity of grain goes through the applicator without receiving treat-
ment. An untreated pocket of wet grain in a bin could cause extensive
spoilage. For this reason, most applicators automatically shut off the
auger if the acid flow stops. The key to successful grain storage treat-
ment is to apply enough acid uniformly over the grain.
Storage of Acid-Treated Grain
Treated grain can be stored in anything used for ordinary grain, with
the limitation that the acid is corrosive to steel, especially galvanized,
and it may also react with concrete, especially in warm weather. No
special preparation is needed for wooden bins, but steel bins probably
should be protected with plastic sheets or acid-resistant paints. Many
farmers have successfully stored acid-treated grain in bunkers,
makeshift bins, or piles. Storage outdoors in uncovered piles
sometimes has been successful, although heavy rain and mild weather
would almost certainly result in spoilage. Except in emergencies, this
is not recommended in Florida. The grain should be protected from rain
and snow. Covering a grain pile with plastic will keep rain off, but may
result in moisture accumulation and spoilage at the top of the pile. As
a grain mass cools during late fall and early winter, moisture is mov-
ed upward through the relatively warm center of the pile and con-
denses on the cold grain at the surface. The grain moisture near the top
may easily be 10 percentage points higher than the average moisture
level. Ventilation of the space over the grain will reduce condensation.
Moisture migration is a problem in bins as well as piles, and is best
avoided by using forced aeration to cool the grain uniformly. This can
be done with inexpensive equipment using low airflow rates. Grain
should be aerated only enough to cool it to approximately the ambient
temperature. Moisture migration is most likely in large bulks of grain
and in grain put into storage at a warm temperature (60-70 F or
higher). As with dry grain, chemically preserved grain should be
checked frequently to detect temperature changes, insect infesta-
tions, water leaks, and condensation problems to avoid spoilage.
Organic acids are often considered to be relatively weak acids.
However, they are corrosive and require considerable care when
working with them.
They can burn the skin, damage the eyes, and irritate nasal passages.
When treating grain or handling the acids, protective clothing in-
cluding safety goggles, rubber gloves, and an apron should be worn.
Fresh water should be kept close by in case of accidental spillage or skin
contact. Also, breathing fumes during treatment and entering freshly
treated grain bins should be avoided. The acid is quickly absorbed by
the grain, but it would be advisable not to handle the grain or go into
bins for a day or two after treatment. Manufacturers' brochures and
label directions should be consulted for additional safety
Feeding Treated Grain
Acid-treated grain has been fed to all kinds of livestock and poultry
with no reported palatability problems or poor performance. Most
feeding trials have been with acid-treated corn fed to cattle. The
treated corn had generally the same feeding efficiency as corn stored
in an oxygen-limiting silo, with both kinds of high moisture grain be-
ing superior to dry grain.
Because the reports vary as to how much advantage there is in
feeding high moisture grain, it is not possible to state a certain percen-
tage increase in efficiency that one can expect. However, some nutri-
tionists feel that 4 to 6% is a reasonable average for beef cattle.
Acetic and propionic acids are naturally occurring compounds, and
a readily digestible energy source. They are intermediate products in
digestion, produced in particularly large quantities in ruminants. The
quantities consumed in acid-treated grain would not be great enough
to upset normal acid levels in the digestive system.
Advantages of Acid Treatment
The principal advantage of chemical preservatives is that very lit-
tle energy is required to treat the grain. Therefore, the producer is not
dependent on the availability of fuel in order to successfully store his
The cost of the equipment used to apply acid is much less than the
cost of most types of dryers. Therefore, a low initial investment is
another advantage to the producer in that he retains investment flex-
ibility. Furthermore, grain can be harvested and treated at almost any
rate, removing a possible bottleneck created by a low capacity dryer.
Other advantages, such as early harvest date, harvesting at high
moisture, etc., are common to other high moisture storage methods as
Disadvantages of Acid Treatment
The disadvantages of acid treatment lie primarily in three areas,
those of marketing, bin and handling equipment corrosion, and cost.
Grain that has been treated with chemical preservatives may no longer
be sold through the normal marketing channels and must be fed to
livestock. For this reason, the farmer who treats his grain is limiting
the source of his grain sales to livestock feeding operations. Treated
grain cannot be used for seed because it will not germinate, and it can-
not be used for human consumption. Also acid-treated grain like en-
siled grain may not be later dried and sold as shelled corn.
Treated grain also corrodes metal grain bins. There are various bin
wall coatings available on the market which will reduce this corrosion,
but the costs of these products can prohibit their use. Equipment us-
ed to handle treated grain is also subject to corrosion. Because of cor-
rosion problems, a producer who plans to store treated grain should
add the cost of reduced bin and handling equipment life expectancy
to the overall cost of acid application. Acid treatment may also
deteriorate concrete, so concrete walls and floors should be protected.
The cost of applying acid to grain depends on many factors, including
the initial moisture content of the grain, the length of time it is to be
stored, the cost of the acid, and the quantity of grain that is to be
treated. Economic studies in the last few years concerning the use of
acid treatment on grain indicate that this method is relatively more ex-
pensive than traditional methods of drying and storing, although many
economic questions are unanswered. The selection of acid treatment
must be based on factors other than costs. These factors include con-
venience, speed and ease of handling, investment flexibility, a
preference (in addition to higher feed efficiency) for feeding high
moisture corn, and low initial capital requirements.
The choice of system for any particular farm will be based on the
relative weight that the farmer places on the economic and non-
economic factors involved in the decision. Grain preservatives pro-
bably have their greatest potential on small livestock farms and on
farms where production has expanded beyond current drying capaci-
ty. The investment flexibility, low capital requirements, and
preference for high moisture corn provide incentives that counteract
the disadvantages of higher cost.
This publication was promulgated at a cost of $623.82, or 29.7 cents per
copy, to increase knowledge and skills of producers of high moisture grain
storage in Florida.
COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORI-
DA, INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES, K. R.
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rates or copies for out-of-state purchasers Is available from C. M.Hinton, Publications
Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida
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