Food and Agriculture Organization of the United Nations
CORNMEAL-MASA
CORNMEAL-MASA
1.- General Information
Cornmeal by definition is dried corn kernels that have been ground in one of three textures –
fine, medium, or coarse. It is a popular dry corn because of its long shelf life, freedom from
black specks, and bright colour. There are two methods of grinding. The old-fashioned water-
ground (also called stone-ground) method – so named because water power is used to turn
the mill wheels – retains some of the hull and germ of the corn. Because of the fat in the
germ, water-ground cornmeal is more nutritious, but will not keep as long and should be
stored (up to four months) in the refrigerator.
The other method to grind the maize is performed by high speed, big volume steel cylinders or
hammer mills. Cylinder mills grind grains with rigid or smooth pairs of cylinders that rotate at
high speed. Grains are forced between the cylinders which grind and tear the kernels instantly.
Cornmeal can be yellow, white, or blue, depending on the type of corn that is used. Yellow and
white corns are the most commonly used for cornmeal. Both grits and polenta are made from
dried corn kernels; the difference is how those kernels are milled. When the corn is ground,
the coarser particles become GRITS, while the finer granules are used for POLENTA. Stone-
ground grits have a chunkier texture and a more "corny" flavour than quick grits. They do take
longer to cook than their counterpart, and they also need more stirring to release the starch
and soften the grains, but stone-ground grits are certainly worth the effort.
2.- Cornmeal Processing details
2.1-Cleaning
The manufacturers should clean the maize correctly before the processing, using blowing
machines and grading equipments.
The maize is separated from the impurities (stones, straw, insects and others) using sieves.
This separation, besides contributing to the high quality, prevents the wear and tear of the
equipments.
2.2.-Degermination
The present method of producing a cornmeal involves first degerminating kernels of corn so as
to separate the horny endosperm portion of each kernel of corn from the remainder of the
kernel.
An efficient corn degerminating system consists of 3 major parts; a hydrator, a degerminator
and a grain polisher. The hydrator applies moisture uniformly to each maize kernel by means
of its slow moving mixing paddles and vibrating housing. It accelerates penetration of moisture
through the bran skin and into the germ. By controlling the quantity of moisture added to the
grain and the retention time of the grain in the hydrating cylinder, efficient pre-conditioning is
accomplished. By the action of moisture, the bran and the germ are encouraged to separate
from the core endosperm of the kernel.
In the degerminator, maize enters the annulus formed by a multiple sided perforated screen
and an eccentric shaped rotor. Its vertical configuration allows uniform and even action on
corn being processed. As the rotor turns, the clearance between the rotor and the screen is
constantly changing. Because of this constantly changing clearance with each rotation, a cyclic
compression and relaxation occurs in the grain bed. This produces both the effective rubbing
action and the pressure necessary for efficient removal of bran and germ, while at the same
time controlling breakage to produce a maximum number of large pieces of pure endosperm
and limiting fines to a minimum.
In combination with abrasive action resulting from the grain moving across specially designed
textured surfaces, this rubbing action simultaneously removes bran and germ from the kernel.
The bran and germ then exit the chamber through the perforations in the screen, leaving the
clean endosperm to exit at the discharge of the machine. A weighted discharge gate, which
can be set manually or automated, is used to regulate the work done and thus the degree of
bran and germ removal.
The third key piece is the grain polisher. The grain polisher also uses an eccentric rotor in a
polygonal screen to produce cyclic compression and relaxation. It uses lower pressures than
does the degerminator. The grain polisher is ideal for the removal of bran only, as is the case
when recovery of large germ particles is desired. It is also suitable for secondary polishing of
recovered endosperm. In addition, it allows the possible production of value added products,
because the flaking grits produced will have very low fat contents and levels of contaminants,
such as insect fragments, microbial activity, insecticide, and fertilizer residues.
Cornmeal Processing Details
2.3.-Milling
The cleaned grains are taken to the mills, where they are completely ground. The hammer
mills are more commonly used, even though, there are small factories that use the stone
ground to the small scale processing.
Stone Milling
The grains can be ground using a system of two matched carved stones; one is stationary and
the other rotates at 500-700 rpm. Volcanic and synthetic (aluminum oxide) stones are widely
used by the industry. Synthetic stones have the advantage of long lasting.
The typical stone is 10.2 cm thick, 40.6 cm in diameter, and carved radially. The grooves
become progressively shallower as they approach the perimeter of the stone. The number,
design, and the depth of the grooves vary with the intended product.
Hammer Milling
Currently, where the electric power is available cornmeal industries are using the hammer mill
that offer easier facility of work, greater capacity per size and easier maintenance.
Hammer mills use rotating hammer or knives to break-up product that has been fed into the
chamber of the machine. The rotating hammers or knives in the chamber of a hammer mill
reduce the side of the product by impacting the product and by forcing the product to impact
the interior of the chamber. The hammers within the chamber of a hammer are sized so that
the end of the hammer almost impacts the interior wall of the chamber. A hammer mill has a
screen to form the bottom of the chamber. Once the product has been reduced to the proper
size, the product falls through the screen below the chamber.
When are used hammer mills to process grain, several factors may be changed to increase or
decrease particle size. The size of the openings in the hammer mill screen greatly determines
the size of the particles that are produced. In general terms, feedstuffs that have passed
through a 1/8- to 3/16-inch screen have an average particle size of 600 to 800 microns.
Screens of one-fourth to three-eighths of an inch normally produce particles that are 800 to
900 microns. However, it is difficult to relate a screen size to specific microns because of
equipment variations such as tip speed, wear, moisture content of the grain, and other factors.
2.4.-Sifting
The corn meal particles after grinding may then be sifted, which separates the corn meal
particles according to their size.
2.5.-Packaging
The cleaned grains are taken to the mills, where they are completely ground. The hammer
mills are more commonly used, even though, there are small factories that use the stone
ground to the small scale processing.
3.- Masa - General Information
Masa is the raw material from which traditional products such as tamales, pozole, atoles,
tortillas, corn chips, tortilla chips, and other products are made. The traditional method to
process corn into masa, called nixtamalization, was developed by ancient Mesoamericans. In
the nixtamalization process, water containing lime is used to cook the grain, although the
leachate of wood ashes can still be used (common in some villages in Mexico and Central
America).
The alkaline cooked corn, called nixtamal, is washed to remove excess lime and pericarp
tissue, and stone ground to form a dough called masa, which is, then, dried and ground into
flour. The major advantage of using dry masa flour is the product flexibility and its improved
shelf life.
4.- Masa Processing details
4.1.-Alkaline Cooking
The first step to process corn into masa is the alkaline or lime cooking. Different forms of lime
(CaO and Ca(OH)2) mined from local sources are used. The solubility of lime in water
decreases as the temperature increases. Only 0.67g of lime can be solubilized per litre of water
at 79.5ºC, whereas 1.2g/L can be solubilized when the temperature drops to 21ºC. Lime
treatment facilitates pericarp removal during cooking and steeping, controls microbial activity,
affects the flavour, aroma, colour, shelf life, nutritional value and improves gelatinisation.
The temperature of cooking depends on the product that the masa will be processed, but it can
range between 85 and 98ºC for 5-40 min.
During cooking, the starch is partially gelatinised, and other grain components are hydrated
and altered.
Cooking depends on the characteristics of the corn and the interaction of temperature, time,
lime concentration, size of cooking vessel, and frequency of agitation.
Optimum cooking and steeping time are determined subjectively by evaluating the extent of
pericarp removal, kernel softening, and overall appearance of the nixtamal.
The steep liquor (called nejayote) is drained, and the cooked-steeped maize is processes in the
next step. Nejayote waste is highly alkaline, with high chemical and biological oxygen
demands, and is considered an environmental pollutant; thus it has to be properly treated
(aerobic treatment, bioreactor, etc.) before discarding.
4.2.-Whashing and Draining
The clean nixtamal is stone ground, using equipments very similar to the ones described for
cornmeal. Stone milling operation is a very important step, because it distributes the hydrated
starch and proteins throughout the ungelatinised portion of the endosperm, forming the masa.
The degree of grinding dictates the type of masa produced: Masa for table tortillas must be
fine ground, and more hydrated (55-58%), whereas coarse, less hydrated (51-53%) ones are
preferred for fried products, such as tortilla chips.
After grinding, the nixtamal contains 48-53% moisture, and is ready for further applications.
In recent commercial productions, the masa can be dried and milled to originate dry masa
flour, which is advantageously distributed for domestic and industrial purposes due to its
prolonged shelf life and convenient preparation. Drying is, though, a critical operation and is
generally done by air suspension or belt dryer. Warm air flows countercurrent to the masa,
which must be dried to a moisture content of about 8-10%. The dry particles are hammer
milled, sieved for different particles sizes and may be blended to produce dry masa flours with
optimum particle size distribution for different applications. Flour is packaged in paper material
with an inner layer of polyethylene to restrict moisture uptake and improve shelf life.
4.3.-Stone Milling
The clean nixtamal is stone ground, using equipments very similar to the ones described for
cornmeal. Stone milling operation is a very important step, because it distributes the hydrated
starch and proteins throughout the ungelatinised portion of the endosperm, forming the masa.
The degree of grinding dictates the type of masa produced: Masa for table tortillas must be
fine ground, and more hydrated (55-58%), whereas coarse, less hydrated (51-53%) ones are
preferred for fried products, such as tortilla chips.
After grinding, the nixtamal contains 48-53% moisture, and is ready for further applications.
In recent commercial productions, the masa can be dried and milled to originate dry masa
flour, which is advantageously distributed for domestic and industrial purposes due to its
prolonged shelf life and convenient preparation. Drying is, though, a critical operation and is
generally done by air suspension or belt dryer. Warm air flows countercurrent to the masa,
which must be dried to a moisture content of about 8-10%. The dry particles are hammer
milled, sieved for different particles sizes and may be blended to produce dry masa flours with
optimum particle size distribution for different applications. Flour is packaged in paper material
with an inner layer of polyethylene to restrict moisture uptake and improve shelf life.
Document Outline - CORNMEAL-MASA
- Masa Processing Details
- CORNMEAL-MASA.pdf
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