Processing of Barley

Introduction

            Barley is one of the world’s oldest domesticated crops and competes with wheat for the honor of being the first wild plant form through under cultivation. Barley (Hordeum vulgare) is the world’s fourth most important cereal after wheat, rice and maize.

            Barley is one excellent source of B-complex vitamins and minerals. Like other cereals, barley is also considered nutritionally poor due to low content of essential amino acids like lysine and threonine. However, breeders have discovered high lysine barley genotypes, which indicate the scope of nutritional improvement in this crop.

            Barley genotypes have been classified as hull less and hulled ones. Barley and oats are unique among cereals, containing relatively high concentration of the mixed linked (1-3), (1-4), b-D glucans (b-glucans). Hulled barley contains 3-7 per cent b glucans while hull less may have as much as 16 per cent b-glucans.

Classification

• Genus - Hordeum
• Tribe - Triticeae
• Subfamily- Festucoidese
• Family - Gramineae      

Barley is a grass of the family Gramineae, subfamily Festucoideae, tribe Triticeae and genus Hordeum. 

Structure

a.   Plant :  Barley has overlapping auricles compared to wheat (smaller non-overlapping auricle) and oats (rudimentary auricles), which are readily distinguished at the seedling stage.

b.  Spike : The spike is made up of spikelets with three florets attached to each of the nodes of the rachis. Two sowed barleys have one, fertile florets, whereas six sowed barley have three. The flowers are arranged in spikelets on the head and are attached at nodes of central stem. The spikelet is composed of the male and female flower parts enclosed within the lemma and palea. The rochilla is attached to the germ end of the kernel and lies in the furrow of the palea.

c.  Kernel : The mature kernel is composed of the hulls (lemma and plea) enclosing the caryopsis and of the rachilla. In most varieties, the hulls are cemented to the caryopsis and make up a part of the threshed kernel.       

In nobed or hull less barleys, the kernel threshes free as it does in wheat. The kernel dry weight is made up of approximately the following percentages of tissue; husk and pericarp 10% aburone and associated testa pigment strands and some nuclear tissue, 14%, starchy endosperm and nuclear remains in sheaf cell region, 73%, embryo, 3%.

Classification of Cultivated Species :

            Plants of the genus Hordeum of the grass family Gramineae, have simple species. The cultivated types of barley and the two most closely related wild forms are included in the section Cerealia. Wiebe and Reid (1961) classified cultivated barleys into three species on the basis of brittleness of the rachis and number of kernel rows on the spike. They also gave detailed descriptions of taxonomic characteristic for growth characteristics of varieties commonly grown at the time.

            Most of the cultivated barley have been classified into the two groups, H. vulgare L., the six sowed barleys, and H. distichum L., the two sowed types.

Two Sowed Types (Hordeum spontaneum C. Koch, Hordeum agriocrithon Aberg) : It was considered to be the progenitor of cultivated six row barleys. This barley has a tough rachis and is not found in the wild away from areas of cultivated barleys. In the common two-rowed group, the lateral florets are sterile and greatly reduced. Only, one row of kernels develops on each side of the spikes. The kernels are all symmetrical and more uniform in size than the six-row barley, but the kernels that develop at the base and at the tip of the spike are often somewhat smaller than those in the center.

Two Rowed Barleys : Three kernels develop at each rachis node. The median kernel is slightly larger than the lateral kernels on each side and is symmetrical in shape. The two lateral kernels are twisted and the twist is more pronounced at the attachment end of the kernels.

Production of Barley :

            The world area under barley cultivation has been steadily increasing. The production increased from 83 million tones in 1961-62 to 132 million tones in 1971-72 and to 162 million tones in 1980. The chief barley producing countries in the world are the USSR, USA and Canada.

            In India, barley is grown mostly in the northern part of the country. The area under cultivation was 0.72 million hectares in 1951-52 which rose to 1.75 million hectares in 1980, which a production of 1.6 million tones. The yield is the order of 7.5 to 9.0 quintals per hectares as against a world average of 19.5.  In India, production is largely confined to Utter Pradesh, Punjab and Haryana but however it can be grown anywhere the wheat can be. In Haryana, barley crops cover 58000 hectares of land area and total yield is 160,000 tonnes.

Chemical Composition of Barley :

            Barley grain is rich in starch and sugars relatively poor in protein, and every low in fate. The husk (lemma and palea) is mostly composed of lignin, pentosans, mannan, uronic acids, hemicelluloses and cellulose fibres. Silica is present in the outer walls of the husk and the awns contain large amounts of silica. The paricarp lacks lignin. The testa contains crude cellulose and pigment strands of alpha waxes, which are a barrier for chemical substances and microbes polyphenols which may complex with proteins are abundantly in the pericarp, testa and aleurone layer. The aleurone has thick cell walls composed of arabinoxylans and has aleurone grains of protein and phytic acid, pherosomes rich in fat and abundant minerals. The subaleurone layer of the endosperm is composed of about 8.5-8.9% starch enclosed in cell walls. b-glucans make up 75% of the cell wall and the rest is arabinonxylons. The embryo consists of about 7% cellulose, 14-17% lipids, 14-15 % sucrose, 5-10 % raffinose, 5-10% ash and 34% protein. The cell wall of the embryo contains uronic acids, pectin and hemicellulose.

A. Carbohydrates

(i) Starch : Starch is a polysaccharide, µ-glucan, and can be divided into straight chain amylose and branched chain amylopectin. The starch granules in the barley endosperm are laid down within amyloplasts and fall into two size groups 1.7-2.5mm and 22.5-47.5mm. These starch grains contain traces of lipids, minerals, proteins and nucleotides. The starch is synthesized in plastids. The “disatatie” enzymes responsible for degrading the starch in germination are phosphorylase, µ-glucosidase, µ-amylase, b-amylase, debranching enzymes and transglucosylase. In normal barleys the ratio of amylose to amylopectin is about 1:3, in high amylose glacier about 1:1, and waxy barley is 97-100% amylopectin.

            Barley starch has A and B granules similar to those making up wheat starch. The smallest granules (<2.7 microns) constitute about 74% of the total, the largest (>13.6 microns) about 9.4% and those of intermediate size about 16.6%. The larger starch granules of barley have a higher amylopectin percentage and a lower gelatinization temperature than the smaller granules.

(ii)  Soluble Sugars : Glucose and fructose are found free and in combination, whereas other monosaccharide are polymerized as oligosaccharides, polysaccharides, glycosides, glycolipids and glycoproteins. Soluble sugar content of normal barley is about 2-3%, hullless barleys 2-4%, high lysine barleys 2-6% and high sugar barleys 7-13%. The total sugars and reducing sugars declines from anthesis to maturity, whereas non reducing sugars are constant in amount during plant growth. The major sugar of living tissues of barley is sucrose.

(iii) Non Starch Polysaccharides : Briggs defines these polysaccharides in barley as ‘pectin fractions’ or Hemicellulosic materials, which are then divided into gums of soluble in hot water and hemicellulose if soluble in alkali. The material removing after delignification and removal of gums are ‘hemicellulose’. Endosperm gums consists of b-glucan and an arabinoxylan. Barley, like oats has a relatively high b-glucan content and barley cultivars of the waxy starch type consistently have greater b-glucan concentration (about 50 % more than standard barleys). Some of the b-glucan of very large molecular weight are not water extractable and cannot be considered gums, though they are part of the dietary fiber content. The small amount of cellulose which is present in the grain (about 4 to 5%) is located mainly in the cell walls of the aleurone-testa tissues. Fructosans can be detected during the ripening of barley, the final level being about 0.5 to 1%.

B. Protein :

            The two major groups of storage proteins in barley are the glutelins and the protamines, present at levels of around 4% each, with somewhat more glutelin than protamine (hordein). The limiting amino acids in barley protein are lysine followed by methionine, threonine, and tryptophan. In barley, the albumins and globulins (soft soluble) which are rich in lysine (5-7%) and threonine, are mainly metabolic proteins. The prolamines are the major shortage proteins of the endosperm and are low in lysine (<2%). The glutelins also found in the endosperm, are associated with found structural proteins of the membranes and are about 4% lysine. Some protamines (hordien) are also present in the protein, bodies of the aleurone cells. The albumins and globulins include the enzymes, they are found mainly in the embryo and aleurone.

            The content of peptides and free amino acids in ungerminated barley is low, normally less than 0.2% of the grain.

•             Albumin - 10%
•             Globulin - 20%
•             Hordeins  - 30%
•             Glutelins  - 40%

C. Lipids :

            Barley lipids content is low (2-3%) compared to maize and oats. Tryglycerides comprising 77.9% of barley lipids contain palmitic acid and the unsaturated fatty acids, oleic, linoleic (principle one of barley kernel) and linolenic. The barley kernel also contains diglycerides, free sterols, free fatty acids and sterol, esters and hydrocarbons. Most of the lipids are in the endosperm (77%), embryo (18%) and hull (5%). The fat content of a developing plant increased and then may decrease slightly. About 78.2% of the total is neutral lipid, 7.3% glycolipid and 14.5% phospholipids. The fat content of normal covered, normal hull-less, high sugar and high lysine barley range in percentage from 1.9 to 2.4, 2.4 to 3.9 and 4.4 to 7.3 and 2.9 to 5.8, respectively. Low levels of waxes, free sterols alkyl resorcinol, carotenoids, nonthophylls, and tocopherols have been reported. Over 4% of total lipid occurs as linolenic acid. Less than about 1% of stearic, palmitoleic and myristic are typically present.

D. Vitamins :

            Barley is and excellent source of the vitamins thiamine (B₁), pyridoxine (B₆), riboflavin (B₂) and pantothenic acid. It is also quite high in niacin. Vitamin E is present in the as a mixture of tocopherols which is present found at levels of about 6 to 45 mg per gram of oil. Some biotin and folacin are also present but carotenes or vitamin A, B₁₂ or D are found in ungerminated grains. The description of vitamin contents are as follow:

•             Choline :    0.9 to 2.2 mg
•             Thiamine :   1 to 16 mg
•             Riboflavin :   0.8 to 3.7 mg
•             Nicotinic Acid :  47 to 147 mg
•             Pentothenic :  3.7 to 4.4 mg

            (As Calcium Salt)

•             Biotin : 0.05 to 0.1 mg
•             Inositol : 1.4 to 3.2 mg
•             Pyridoxin : 2.7 to 11 mg

            Embryo scutellum and aleurone contain more vitamins than the other tissues.

E. Minerals :     

            The distribution of minerals is uneven throughout the kernel and the rachis (5-14%) and owns (17-38%) contain a large portion of the minerals. The ash content of barley ranges from 2.2 to 3.9%. The phytic/nonphytic phosphorus ratio of barley was about 2 in barley compared to 3 in wheat and oat and 13 in rye. These ratios are meaningful because phytic acid decreases the availability of certain minerals. In the whole kernel of barley the minerals present in greatest amount are phosphorus (2.97 g/kg), potassium (4.39 g/kg) and magnesium (1.29 g/kg). Calcium and sodium are found in much lower levels 0.257 and 0.138 g/kg, respectively. Still lower, but significant quantities of iron, zinc, magnesium, and aluminum are present 28, 23 and 10 micrograms per kg, respectively. Traces of copper and molybdenum can found.

F. Phenolic Compounds :

            In plants the phenolic compounds can be divided into benzoic acids, cinnamic acids, terpenoids, and flavonoids. Barley contain a wide range of phenolic compounds in one form or another ranging from free and combined tyrosine, tyramine and derivatives, phenolic acids, esters and glycosides and numerous other phenols though lignons and substance related to lignons. Phenolic compounds may also inhibit nutrient utilization.

Milling of Barley

            Barley is millet to make blocked barley, pearl barley, barley grots, barley flakes and barley flour for human consumption. Removal of the hull or husk of barley, which is largely indigestible is and important part of the milling process.

Intrinsic qualities : The milling is done in barley to achieve :

1.      Absence of sprouting.

2.      Absence of discolouration due to weathering.

3.      Freedom from fungal attack and insect infestation or damage.

4.      Soundness of appearance.

5.      Absence of undesirable aroma or flavour.

The harder types of barley is best for milling purposes because the hull and bran can easily be removed from endosperm by superficial abrasion and yielding particle will retain the shape of the whole grain. The softer grains are not better because they would tend to fragments, leading to a reduction in the yield of first quality products.

            Barley for milling should have as low as hull intent as possible. The presence of damaged grains lowers the quality of milling barley. Such grains frequently reveal areas of exposed endosperm where fungal attack may occur leading to discolouration and intrigues discoloured particles to the finished products. Thin grains also lower the milling quality with a higher hull content than normal they make a small contribution to the yield of milled products.

Operations : the sequence of operations in barley milling may be summarized as follows.

1. Preliminary Cleaning : Barley is cleaned on machines similar to those used for wheat cleaning, viz. milling separators, drier cylinders or indented dishes, and aspirators. The sizes of sieve aspirators and indents are modified for the comparatively larger size of barley grains.

2.   Conditioning : Conditioning consists in adjustment of moisture content to about 15% by drying or damping and resting for 24 hour.

3. Bleaching : Barley is used to bleach with moisture and sulphur  dioxide. Blocked barley is fed into a vertical earthenware cylinder. Into which steam and sulphur dioxide are injected. The quantities used are 1-2% of moisture and about 0.04% of sulphur dioxide and solution of sulphurous acid (H₂SO₃) or of sodium disulphide (NaHSO₃) can be. The treatment take about 20-30 min time, after that the barley is binned for 12-24 hour for the bleaching to take effect. Excessive quantities of sulphur residues in the final product should be avoided.

4. Blocking and Pealing : Both blocking and pearling of barley are abrasive scouring processes differing from each other merely in degree of removal of the superficial layers of the grain batch machines or the rate of throughput  in continuous working machine.

5.  Aspiration : Aspiration of the pearled grain to removes the abraded portions and cutting of blocked barley into portions known as grits and it is similar to those methods done for aspiration of oatmeal. In Germany, the blocked barley is first cut into grits, the grits graded by size and then sounded in the pearling machine.

6. Polishing : The pearl barley is polished on machines similar to those used for pearling but equipped with stones made of hard white sandstone instead of emery composition. The average yield of barley is 67% of the whole barley.

7. Steam Cooking and Flaking : Barley flakes are made from pearl barley by steaming and flaking on large diameter smooth rolls.

8. Drying : The flakes are dried to about 10.5% moisture content before packing. Barley flakes are made from pearled barley has been used as flavouring ingredients in specially breads in the USA.

            Pearl barley is used for sups and dressings and for the manufacture of puffed barley, a read to eat breakfast cereal. Pearl barley blocking removes part of the husk, this process must be accomplished with the minimum of injury to the kernels. The pearling carried out in two stages, removes the remainder of the husk and part of the endosperm. The three processes remove about 5%, 15% and 11%, respectively to yield a final product representing about 67% of the grain.

Three types of blocking and pearling machine are in general use :

(i) A fetch machine consisting of a large circular stone, faced with energy cements composition and rotating on a horizontal axis within a perforated metal cage.

(ii) A continuous working machine consisting of a rotator faced with absorsive material rotating on a horizontal axis within a semicircular stator lined with the same material, the distance between rotor and stator being adjustable.

(iii) A continuous working machine comprising a pile of small circular stones rotating on a vertical axis within a metal sleeve. The annular space between the stones and the sleeve occupied by the barley being strongly aspirated. The barley bolls between the rotator and the stationary part of each machine in bouncing from one surface to the other the husk is split or subbed off. The degree of treatments is governed by the abrasiveness of the stone flung by the distance between rotor, and station and by the time of treatment in is also a starting material for the manufacture of barley flour. Milled barley are also used for extruded food snacks as croutons and salad dressing as crunches for nut substitutes.

Barley Flour

            Barley flour is milled from pearl barley, blocked barley or unpearled hull less barley. Optimum tempering conditions are 13% moisture content for 48 hour for pearl barley, 14% moisture content for 48 hour for unpearled hull less barley. The milling system uses solar mills with blunted and smooth rolls and plansitfers.

            When blocked barley or whole barley is used for milling barley flour, due allowance must be made for the greatly increased quantity of by products, which would otherwise hope the system. Barley flour is also a by products of the cutting, pearling and polishing processes. 

                     

Barley Types	Extraction Rate
Pearl barley	82%
Original whole grain	55%
Blocked barley	59%

            

A blend of hull less barley and wheat can also be milled at the ratio of 10:90 to 20:80. When barley flour was blended with wheat flour in ratio of 10:90 to 30:70, bread characteristics were better with hull less barley flour than with hulled barley flour, but bread quality deteriorated as proportion of barley flour increased.

            Barley flour is used in the manufacture of flat bread for infant food and for food specialties. It is also a component of composite flours used for making yeast raised bread.

            Pre gelatinized barley flour which has high absorbent properties provides a good binder and thickener. Combining pre gelatinized barley flour with barley crunch makes barley breading.

            The coarse by products from the blocking process are fragmented on a chamber mill and the ground product combined with the residues from the two peeling operations for use as animal feed.

Malted Barley Flour

            Barley malt is ground or milled to make malted barley flour. Malt flour is used as a high diastatic supplement for bread flours, which are low in materials diastatic activity, as a flavour supplement in malt loaves and for various other food products.

Air Classification : Malted barley flour can be our classified to yield protein rich and protein poor fractions. The former used in the food industry, while the later is used to make unique beer.

            Other products derived from malt include kibbled malt, malt extract and cereal syrups. The major food uses for malt products and cereal syrups are in bread, biscuits, crackers, crisp breads, breakfast cereals, infant and invalid foods, matted food drinks, pickles and sauces, sugar confectionary and vinegar.

Molting

            Molting is a controlled natural process rather than a manufacturing operation. Essentially barley kernels are allowed to grow under precisely defined conditions in order to bring about specific, desirable changes in the physical and chemical properties of the kernel. Growth is then stopped by removal of water. Flavour components are developed by gently heating and curing the malt.

            Finished malt resembles barley, but only superficially. Within the kernel, natural enzymes formed and stimulated by controlled moisture, aeration and temperature have:

1.      Broken down cell wall material in the endosperm,

2.      Rendered some of the protein soluble in water,

3.      Started to degrade some of the starch granules fermentable sugars.

Barley is cleaned, sized, segregated by variety and protein content and stored for several months to break any dormancy. The amount of water-soluble extract obtained from malt is dependent to a large extent on the amount of starch in the kernel. From this extract, brewers produce beer. Low protein (13% dry basis or lower), plump kernels have a higher proportion of starch and other factors being equal produce a higher quality brewer’s malt.

The following steps are involved :-

1.   Cleaning and Grading : On intake, barley is cleaned to remove dust, chaff, weed seeds, thin barley and other grains. Cleaned barley is graded according to size plump and medium grades of barley, retained in sieves with slots 2.5, 2.4, 2.2 and 2.0 mm wide or 2.2 mm sieve is too thin for malting and is sold as feed.

2. Steeping : Growth is initiated by the absorption of water into the kernel in conical bottomed steep tanks. Water at 12-16⁰C and air, respectively are provided to barley over a period of 40-48 hour. Water enters the embryo through the micropyle, a small opening, until the moisture content of the kernels rises to 44 to 46%. The water is changed every 6-8 hour and is never recycled. Molt houses create a significant volume of effluent with a high BOD. Compressed air bubbled through the steep agitates the barley to ensure all surfaces are washed.

Gibberellins, plant hormones, are synthesized by the embryo and diffuse to the aleurone layer of the barley kernel. Here they stimulate the production of the hydrolytic enzymes capable of degrading barley starch granules, protein and nucleic acids. Enzyme production also takes place in the embryo.

Later aerations remove the carbon dioxide from as a respiratory product of initial growth

3.   Germination : From the steep tank, the barley falls by gravity or is gently conveyed to the germination vessel. Over a period of four days at 13-16⁰C and 100% humidity the barley grows. The bed is gently turned by machine to prevent the soot lets from malting and to promote uniform growth throughout the bed. Using large volumes of air and water sprays, the temperature is controlled and carbon dioxide removed. Germination is considered complete when the endosperm is fully modified which means:

(i)  The cell walls are largely dissolved to expose the starchy interiors of the cells.

(ii)  Those catabolic enzymes are formed which will convert high molecular weight carbohydrates to low molecular weight carbohydrates and sugars.

(iii) Degradation of some proteins to soluble peptides has begun. These peptides will nourish yeast in the fermentation process; some will remain in the finished beer giving it mouth feed and tenure. Fully germinated barley is called green malt. Germination is carried out in drums on rotating floors, in salad in boxes or the wonder houfen system 

4. Kilning : Kilning can be carried out in the same vessel as germination. To save energy, kilns are often arranged on two levels, one directly above the other. Initiate drying takes place in the upper kiln, using the residual moisture removing capacity in the warm air coming from the lower kiln. Air fully laden with moisture is then exhausted to the atmosphere.

To prevent denaturation of the enzymes required by the brewing process, green molt is gently dried. The drying air temperature is increased from 50⁰C through various levels to a final temperature around 80⁰C. Air forced through the fed gradually lowered the moisture content of the malt to 4%.

Later stages of kilning are referred to as the curing process, during which most of the flavour components of malt are generated. These are predominantly heat induced chemical compounds called maillard reaction products; they characteristically develop when amino acids and sugars are heated together. Following kilning the brittle rootlets are easily removed and role as a high protein (75% dry basis) feeds supplement for livestock.

The malt is stored, often for reversal weeks to regain homogeneity and equilibrium, prior to blending and shipment.

The yield of malt from barley is about 75% some typical losses consist of:

• Cleanout from raw barley - 7-9%
• Respiration during steeping and germination - 4-5%.
• Drying (barley, 13.3%, malt 4%) -  9-10%
• Malt rootlets and hulls - 3-4%

5.  Malt Analysis and Shipment :  Control of all aspects of the steeping, germinating, and kilning process must be reliable and precise. Variances as small as 1% in the moisture level or 1⁰C in the temperature have a significant effect on the analytical values of the final malt.

Use of Malt : Special malts such as caramel, black, amber roasted, and Munich malts impart colour and additive flavour to beer. They are produced by various degrees of roasting, to the concomitant detriment of the enzymes. Peat malt has the savor of peat smokes. Crystal malt is green malt rapidly heated. The interior is glassy and the taste is luscious.

            Distiller’s malt with its high enzyme activity and less emphasis on flavour is produced by kilning at low temperatures. Hopped malt extracts are used in specially breweries and home brewing kits.

Other uses for malt are in baking, confectionary and breakfast foods.