Cereal Grain Processing: From Storage to Milling
Gas Production and Dough Ripening
Gas Production and Retention: CO2 generated does not create bubbles; it only inflates them. It depends on sugar content. Gas retention depends on gluten.
Dough Ripening: Fermentation and mechanical manipulation make the dough less sticky and more rubbery. Elasticity and spring are relaxed. Oxidation agents might be needed.
Crust and Crumb Color
Crust Color: Brown due to Maillard reactions (amino acids and reducing sugars).
Glaze: Due to starch gelatinization.
Crumb Color: Related to flour color, ingredients, and fermentation (gas production).
Bread Aroma and Flavor
Crust Aroma and Flavor: From interaction among reducing sugars and amino compounds, and aldehydes production.
Overall Aroma and Flavor: From alcoholic and lactic acid fermentation.
Chorleywood Bread Process (CBP)
The CBP process is characterized by:
- Considerable amount of work on the dough (11 W/kg; 40 J/g) during a period of 2 to 4 min.
- Chemical oxidation with ascorbic acid, potassium bromate, azodicarbonamide.
- Addition of fat, about 0.7% on flour weight, of which 5% should be high-melting point fat (solid at 38 °C).
- Use of extra water: 3.5% more than normal.
- A higher level of yeast, 2% on flour weight.
- A first proof of 2 to 10 min after dividing and rounding, followed by conventional molding and final proof.
Advantages of the CBP
Advantages claimed for the CBP:
- An increase in yield of bread of 4%, and thus a net savings on raw material costs.
- A savings of 60% in processing time.
- A savings of 70% of space, previously occupied by fermenting dough.
- A lower staling rate.
Bread Staling and Preservation
Bread Staling: Due to retrogradation, at temperatures below 55°C, from an amorphous to a crystalline form, the latter binding considerably less water than the former.
Effects: A rapid hardening, a toughening of the crust and firming of the crumb, loss of flavor, increase in opaqueness of the crumb, migration of water from crumb to crust, and shrinkage of the starch granules away from the gluten, development of crumbliness.
Bread Preservation: Bread becomes unacceptable because of staling, drying out, loss of crispness of crust or mold development.
To delay mold development:
- Use of propionic acid (3g/kg flour) or its sodium, calcium or potassium salts.
- Use of sorbic acid–impregnated wrappers, gamma irradiation with 5 × 105 rad, or infrared irradiation.
Grain Storage
Storage Purposes:
- Holding stocks on the farm prior to sale.
- Centralization before distribution or processing during the year following harvest.
- Storage of annual surpluses over a longer period.
Unprotected piles on the ground; underground storage; farm barns, containers or vessels; elevator silos.
Centralization: Depends upon the marketing regime: country and terminal elevators, where include equipment for cleaning, drying and conditioning of grain.
Silos vs. Flat Buildings
Silos/Bins vs Flat buildings:
FBs: inexpensive; easy to fill via conveyor; removal can be difficult; lower strength in the sidewalls.
Silos: with conical hopper, the grain flows via gravity; very lower physical floor area to storage tons of grains. Impurities trapped in the central core of the pile (spout-line): overheating and moisture condensation.
HANDLING: mechanical conveyors
Hazards During Storage
Hazards during storage:
- Excessive moisture content, temperature
- Biochemical deterioration
- Microbial infestation
- Insect and arachnid infestation
- Rodent, bird predation
- Mechanical damage through handling
Temperature, Humidity, and Moisture
Temperature and %RH & Moisture content: Moisture content follows nonlinear relationship between equilibrium moisture content and equilibrium RH; affected by T.
Metabolic Changes
Metabolic changes:
Respiration: gaseous exchange occurs; oxygen uptake, increase in CO2, water and heat; weight losses; aleurone and embryo are the tissue involved.
Germination: roots develop from the radicle, and leaves and stem develop from the plumule; enzyme systems are activated; due to moisture migration and condensation; irreversible.
Microbial Infestation
MICROBIAL INFESTATION: Fungal spores and mycelia, bacteria and yeasts are present on the surfaces of all cereal crops. Storage fungi are predominately Aspergillus and Penicillium; less common Fusarium. Production of mycotoxins. Fungi require about 70 to 90% RH. In the presence of oxygen, fungal respiration increases, producing more heat and water. Thus, bacteria easily growths.
DECONTAMINATION: Chemical treatments for aflatoxin: addition of the double bond of the furan ring and oxidation involving phenol formation and opening of the lactone ring. acetic acid, ammonia gas, calcium hydroxide, formaldehyde.
Infestations
INFESTATIONS:
Insects: beetle or moth; arachnids, mites. Most commons: flour mite, grain weevil, rust-red grain beetle. Grain weight losses; hotspots: increase metabolic activity, moisture changes; smell changes; risk for workers; blockage in equipment; facilities damage.
Vertebrate pests: rodents and birds; economic losses and pathogenic risks.
Grain Drying
Drying: Aim: to reduce moisture content.
- Decreasing ability to germinate (malting barley, seed grain).
- Denaturation of gluten (loss of baking quality; livestock fed).
- Fissuring, stress cracks
T at which damage occurs: initial moisture and type of grain. When high T, slow cooling: to reduce stress cracks.
Grain Separations and Cleaning
Separations
SEPARATIONS: Aim: to remove impurities (e.g., broken grains, dust, green plant parts) which are freely assorting material.
Types of impurities: vegetable, animal, mineral matters; miscellaneous rubbish.
- Magnets, metal detectors.
- Sieves: screening and scalping operations (string, straw, stones > grain > sand, broken grains, small seeds).
- Destoners, current of air flows upward.
- Disc separators: to discriminate on the basis of seed length not width.
Cleaning
CLEANING: Aim: to remove dirt adhering to the surface of grains. Use of an abrasive treatment; outer layers of the pericarp may be removed. Grains enter at one end and are cast against the mesh by the inclined rotor beaters; cleaning is achieved by the friction of grains against each other or against the mesh.
Grain Milling
Milling involves the transformation of whole grains into forms suitable for conversion into palatable products; the single term covers a wide range of processes.
- Dehulling: remove of hulls
- Decortication: remove of outer layers; embryo too
- Grinding: reduce the starchy endosperm
Hulls: lemma, palea; fiber, bioactive compounds
Bran: pericarp & outer layers; fiber, protein, and fat
Germ: embryo; fat
Rice and oat milling: dehulling is part of the milling process
Wheat milling: dehulling is regarded as a pretreatment to the milling process.
Barley milling: the process is synonymous with dehulling.
Wet milling: Main process is maceration process; starch, protein and cell wall material bring about a complete dissociation of the endosperm
Dry milling: Water might be used as well during processing but it is not related to bring any component from endosperm.
Rice Milling
Rice milling: Aim: to remove hull, bran and embryo as completely as possible without breaking the remaining cores of endosperm. Two main stages: dehulling and ‘whitening’ or milling. No grinding is completed; unless, rice flour processing.
Drying: moisture at 13-14%.
Dehulling: by abrasion; using plastic, rubber roll hullers or disc shellers.
Parboiling: hot water/steam; to easily remove lemma and palea.
Disc shellers, Rubber roll hullers.
Aspiration: to separate hulls.
Grader: to select whole grains.
Whitening: to remove bran and embryo; using abrasive cone.
Polishing: to remove inner layers, aleurone.
Sifting/sieving: to grade grains into various sizes.
Sorting: to remove nonconforming grains.
Sifting, sorting.
Wheat Milling
Wheat milling: Aim: to produce (white) flours in a range of cooked flour types; to separate the endosperm; to reduce the maximum size.
White flour: from grain of common wheat (not drum wheat), by grinding processes; bran and embryo are removed.
Whole-meal, whole-grain flour: all the grain elements; germ reduces shelf life.
Graham type, more coarsely, not sifted.
Brown flours: white flour and some bran and germ fractions.
Wheat Milling Processes
Breaking: to separate endosperm from bran and germ; to produce large fragments of endosperm.
Scalping: sieving to remove endosperm from bran.
Purifying: to separate only endosperm fractions.
Scratching: to remove some bran fractions.
Reduction: to grind endosperm; to produce flour; interspersed with siftings (Flour dressing).
// La fermentación inicia con la conversión de azúcares complejos a azúcares simples se convierten en CO2 (producción de gas) y alcohol. Se pueden producir metabolitos secundarios como ácidos orgánicos. A mayor fermentación condiciones iddeales ótimas dde temperatura y tiempo mayor producción de CO2. El gas va a inflar las burbujas de aire que se han formado durante batido. La retención dependerá de la red de gluten.