Group Title: Mimeo report - University of Florida Everglades Experiment Station ; EES68- 4
Title: Mechanical dewatering of forage crops
Full Citation
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 Material Information
Title: Mechanical dewatering of forage crops
Series Title: Everglades Station Mimeo Report
Physical Description: 5 p. : ; 29 cm.
Language: English
Creator: Casselman, T. W
Everglades Experiment Station
Publisher: Everglades Experiment Station
Place of Publication: Belle Glade Fla
Publication Date: 1968
Subject: Forage plants -- Dewatering -- Florida   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Includes bibliographical references (p. 5).
Statement of Responsibility: T.W. Casselman.
General Note: Stamped: "Oct 25 1968."
 Record Information
Bibliographic ID: UF00067466
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 63898263

Full Text

/c13 & I---r31
Everglades Station Mimeo Report EES68-4 HUME LIBRARY


T. W. Casselman-/
.FA.S. Univ. of Florida
Mechanical dewatering, as used in this text, will indicate a process "wn- ih-
some of the moisture in forage materials is removed mechanically as a first step
in the processing of a livestock feed. The objective of mechanical dewatering of
forage crops is to reduce the moisture content, without excessive loss of nutri-
ents, to a level that will allow economic thermal dehydration.

All forages when converted into dry feeds with acceptable storage character-
istics must have excess water removed, preferably without appreciable loss of
the desirable nutrients found in the original crop. The time-honored method of
field curing hay, utilizing the sun's energy to remove excess moisture, appears
on the surface to be an economical system. Unfortunately, this system has certain
inherent disadvantages, i.e., leaching and shattering losses due to exposure to
the weather and mechanical handling. In some areas such as South Florida, this
system is impractical due to high humidity, high soil moisture, and frequent
showers. Under these climatic conditions vegetative growth is rapid and lush,
and green weight yields are high but these same conditions are responsible for
the problems encountered in processing high moisture forage. Large quantities
of water must be removed from the plant, and the commonly used methods are either
not adequate or economical. Mechanical dewatering was studied as a means of remov-
ing some of the initial moisture in a forage prior to further processing and the
results of these studies are reported herein.

Since 1942, British researchers have studied the principles of mechanical
dewatering to extract protein from plant materials for.human consumption. Pilot
plant production of plant protein for human consumption has been studied since 1948
(3)2/. In 1963 installation of a bulk protein extraction unit at Kingston, Jamaica
was completed indicating that mechanical removal of juice and nutrients is feasi-

The general procedure has been to pulp the fresh leaves or plants into a semi-
liquid, fibrous mass, before removing the juice in a mechanical press. Pirie (1)
described several-types of mechanical presses which can remove 50 to 90 percent.of
the fluid from a pulp initially containing 80 to 90 percent water. He also reported
that 50 to 60 percent of the protein in the initial crop can be collected in the
expressed juice by this method (2). The protein-containing solids can be separated
from the juice by heat coagulation or acid precipitation. The remaining fibrous
materials from which much of the nutrients and moisture have been removed is gener-
ally discarded, but could be used as roughage for ruminants.

1/ Assistant Agricultural Engineer, Everglades Experiment Station, Belle Glade,

2/ Numbers in parentheses refer to Literature Cited.

3/ Personal communication from N. W. Pirie dated February 27, 1963.

To remove the greatest amount of the protein in the juice, Pirie (1)
recommended that the layer of material after pressing should not exceed one inch
in thickness. As the compressed mat increased in thickness, more of the protein
in the solid mass of forage was retained by the filtering action of the com-
pressed fibers. The expressed juice emerging thus contained less nutrients.
The goal in adapting these principles to the mechanical dewatering of forage
crops should be protein retention in the fibrous portion of the plant.

Italian researchers (4) utilized these principles in the PAST (Prodotti
Alimentari Sistema Tallarico).system to obtain.up to one-third more hay as com-
pared with normal hay making procedures and by avoiding leaf shattering and
leaching losses associated with normal hay making. They reported hay thus made
to be higher in nutritive value than sun cured hay.

Experimental mechanical dewatering of forage crops and potential forage
crops grown in the Florida Everglades was begun in 1955 at the Everglades
Experiment Station. The major objectives of these studies were to determine:
1) the feasibility of dewatering local forage crops using available equipment,
2) the amount of water which can be removed from crops by mechanical dewatering
over a range of initial moisture contents, 3) the effect of pressing on the
nutritive content of various crops, and 4) ways to utilize the pressed forage


Dewatering was accomplished with several screw-type presses of different
sizes4/. These presses are commercially available and are currently employed
in many industrial operations. They contain broken flight augers turning at a
low speed within a cylindrical screen. Each auger section has a pitch less than
the preceding section.

In theory the press operates as follows: as the forage moves through the
press by auger sections of progressively decreasing pitch, the volume moved per
revolution of the screw decreases. Compaction results to generate the pressures
necessary to expel the juice. To aid in keeping the cylinder full and the
pressure constant, a compressed air controlled choke cone at the outlet of the
press is forced against the outcoming forage by an adjustable pressure air
cylinder. Stop bars attached to the frame of the press and extending into the
screw between the flight sections prevent the forage from rotating with the screw
thus causing it to move parallel with the axis of the screw shaft.

The four press sizes used in these early studies were 4, 10, 12, and 16
inches in diameter. The 4 and 10-inch sizes were laboratory models and loaned
by the manufacturer to the Everglades Experiment Station. The 16-inch unit was
installed and operated at a commercial forage processing plant. The 12-inch
press, belonging to the Everglades Experiment Station, was trailer mounted for
field operations.

4/ Presses used in these studies were manufactured by Dan B. Vincent, Inc.,
Tampa, Florida.


Representative samples of fresh forage, pressed forage, and expressed juices
were obtained from a number of laboratory and field experiments and from a
commercial operation for a wide variety of crops. However, certain common con-
ditions were met whenever samples were taken: 1) fresh forage samples were all
harvested and chopped by standard forage crop harvesters before being pressed;
2) in the case of manually harvested crops and vegetable wastes in particular,
efforts were made to simulate the action of the chopping effect of a harvester
as closely as possible; and 3) on all presses the air pressure on the choke cone
was maintained at 40 to 50 psi (pounds per square inch).

For convenience, forage crops and potential forage crops were divided into
four arbitrary classes: pasture grasses, including paragrass, pangolagrass,
Caribgrass, Bermudagrass, St. Augustinegrass, and other pasture type grasses
normally grown in the area; other grasses, including oats, sorghum, sweet corn
stover, and sugarcane tops and leaves; legumes, including white clover and
alfalfa; and vegetables and vegetable wastes such as celery stalks and tops,
turnip tops, endive, and beet tops.


Moisture reduction of fresh forage. The average effect of mechanical de-
watering on moisture removal in terms of the ratio of units of moisture to units
of dry matter (M/DM) over a wide range of moisture conditions for numerous crops
is shown in the graph. The M/DM ratio is numerically equivalent to the moisture
content expressed on a dry weight basis divided by 100. The dry weight basis of
moisture content expression is frequently used in drying studies because the
moisture lost is easily obtained by subtraction. For example, if a fresh sample
enters the press at 85 percent moisture (wet basis) it contain 5.67 units of
moisture per each unit of dry matter (M/DM = 5.67); after leaving the press,
M/DM = 2.33 (refer to the graph and the dashed lines). Therefore, under these
conditions, after treatment by the press, the forage has lost 3.34 units of mois-
ture or over half the original amount of water. An M/DM ratio of 2.33 is equi-
valent to 70 percent moisture on the wet basis. Any M/DM figure can be converted
to moisture content (wet basis) using the following expression:

% moisture wet basis = M/Dm
M/DM + 1 x 100

Thus in the above example when M/DM = 2.33, % moisture = 2.33 100
S+ 1 x 100 = 70.

The amount of moisture removed by the mechanical dewatering press depends
upon several interrelated factors which include initial moisture content, age
of crop, type of crop, preparation of material before pressing and others. It
is evident from the scatter in the data that, even within the same class, the
free hand curve for pressed forage is an average of what occurred when these
materials were pressed under the conditions described. However, the curves do
indicate that the pressing operation became significantly more important as the
moisture content increased.

The upward trend of the curve in the high moisture region prompted the trial
of additional mechanical and chemical treatment of crops prior to pressing. A


shredder, similar to a hammer mill but with swinging blades and without a screen,
was used to shred and macerate material before pressing. In some cases 1-1/4
percent hydrated lime by weight was added to the shredded materials. The table
shows the effects of mechanical and chemical treatments on the reduction of the
M/DM ratio for the crops treated. Shredding significantly reduced the M/DM
ratio in the higher moisture crops. The effect on grasses was not so pronounced,
though it did help in some cases. Addition of lime further aided in the removal
of water.

Unitsmoisture per unit of dry matter (M/DM) for a representative selection of
plant materials that were subjected to several different treatments prior to

Plant Material .Pressed Forage
6 Original Shredded plus
Moisture Content, Fresh Not 1-1/4%
% Wet Basis Forage Shredded Shredded Hydrated Lime

Veg. & veg. wastes
Celery stalks (95.3) 20.3 8.2 5.0 3.2
Endive (94.8) 18.2 5.8 4.1 2.4
Turnip Tops (93.9) 15.4 2.8 -
Sugar beet tops (93.6) 14.6 6.6 3.6 2.0
SMangel (Wurzel) tops (92.9) 13.1 3.6 3.5 2.7
Collards (91.5) 10.8 2.6 -
Stock beet tops (90.8) 9.9 4.8 3.0 2.7
Celery leaves (90.6) 9.6 3.2 2.9 1.5
Pasture grasses
Paragrass (87.4) 6.9 2.3 1.8
Alexandergrass (87.0) 6.7 1.9 2.0
Napiergrass (85.2) .5,8 2.3 2.0
Pangolagrass (82.6) 4.8 1.8 -
Caribgrass (82.2) 4.6 2.2 -
St. Augustinegrass (80.5) 4.1 2.8 2.2
Bermudagrass (77.0) 3.3 1.8 1.8
Other grasses
Oats (88.5) 7.7 2.3 -
Sorghum (82,0) 4.5 1.7 -
Sweet corn stover (77.9) 3.5 2.4 2.5
White Clover (88.0) 7.3 1.6 -
Alfalfa (82.6) 4.6 2.1


o Pasture Grasses
o Other Grasses

o Legumes

A Veg. 8 Veg. Wastes


0 1 )

Fresh Forage



* -- dressed Forage-----------
*--Pressed Forage

i I I I I I I a a I

70 75 80 85 90 95

Units of moisture per unit of dry matter as a function of percent moisture,
wet basis, for fresh and pressed forages

20 a:


I8 <

14 z





.II I I I I I. . .

_..... \

o I



1. Pirie, N. W. The large-scale separation of fluids from fibrous pulps.

Jour. Bioch. and Microbiol. Technology and Engineering 1(1): 13-25.


2. Pirie, N. W. Leaf proteins. Annual Review of Plant Physiology 10:33-52.


3. Pirie, N. W. Some suggestions on the initiation of work on the use of

leaf protein as a human food. Mimeo. Rothsmsted Exp. Sta., Harpenden,

Herts., Britain.

4. Tallarico, G. and B. Fagotti. La conservazione dei foraggi frenchi.

Litostampa. Via Brescia 19, 1957, Rome, Italy.

October 1967
400 copies

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