Defects

Defects in Cheddar cheese arise through contamination of milk with undesirable microorganisms, inadequate acidification during manufacture to attain the optimum compositional factors of pH, salt and moisture. Additionally, physical damage to packaging of vacuum-packed Cheddar can allow the contamination and growth of undesirable microorganisms on the surface of the cheese.

The defects in Cheddar may relate to flavour, body & texture, colour or appearance.Flavour defects may be bitter, acid, fruity, unclean,rancid, etc. The defects in body and texture could be corky, curdy,crumbly, mealy,pasty, short body and gassy and open texture. The colour defect may be acid-cut, bleached discolouration and seamy etc.

i. Flavour

i) Bitterness: Bitterness in Cheddar is associated with the accumulation of hydrophobic peptides which are formed by the action of the coagulants and starter proteinases. Bitter peptides are derived from both ás- and â- caseins.Chymosin is important in the production of bitter peptides, since residual coagulant in Cheddar releases extreamely hydrophobic peptides from â- casein. Cutting the coagulum at low pH in Cheddar manufacture results in the retention of excessive chymosin and the development of bitterness. A low salt content in final cheese will enhance chymosin activity and result in the accumulation of bitter peptides. The overall level of bitterness in Cheddar will depend on the relative rates at which bitter peptides are formed and degraded to nonbitter peptides. Certain Lc. lactis strains are associated with the development of bitterness in Cheddar cheese. These strains survive well at the scald temperature used in Cheddar manufacture and their presence at high numbers in the fresh curd results in high proteolytic activity during ripening. The total proteolytic activity of the starter strains can have a significant effect on the development of bitterness.

ii) Fermented: Fermented flavours are characteristics of the odour of fermented whey. They possess some of the qualities of the combined odours of alcohol,acetic acid and propionic acid. They may appear in cheese soon after it is made, but they usually develop after the cheese is two weeks of age. They are believed to be caused by yeasts or bacteria. These organisms may get into the milk on the farms by contact with unclean and non-sterile surface of utensils,milking machines and milk cans. The occurrence of this flavour defect can be prevented by taking utmost precaution in plant sanitation, by using clean and active starter and ripening the cheese at or below 8°C.

iii) Fruity: Fruity flavours resemble that of ripe fruits such as pine-apple, raspberry etc. These are closely related to the fermented flavour defect. Hence the origin, prevention and remedies may be considered identical to that of fermented.

ii. Body

The term body is used in the cheese industry to designate the physical properties of consistency. These properties include firmness, cohesiveness, elasticity and plasticity.These physical characteristics of cheese are sometimes called rheological properties.Firmness is the property of the cheese which causes it to resist deformation or distortion under pressure. Cohesiveness is the characteristic of the cheese that causes it to stick together. Elasticity is the capability of the cheese to recover its size and shape after deformation. Plasticity is the quality of the cheese which enables it to be deformed under pressure without rupture.

The rheological properties of cheese are affected by methods of manufacture and composition of cheese. Various terms are used to indicate the firmness, elasticity,cohesiveness and plasticity of curd and cheese. These terms describe the appearance and the feeling of the cheese when a plug is removed from the cheese block. A normal plug of ripened Cheddar shows a smooth, uniform surface. It feels solid and firm, it does not crumble when cut or pressed. It bends before breaking and when rubbed between the thumb and fingers, it feels smooth and waxy like cold butter.Some of the common defects are as follows:

i) Corky Body: Cheese with a firm, hard, tough and somewhat elastic consistency is called corky. Such cheese is difficult to crush with the fingers, but when enough pressure is applied it breaks apart in a woody manner. Corky body may be apparent as very firm curd at the time of draining, the characteristics usually appear before salting. Corky characteristics may persist throughout the life of the cheese. This defect may be caused due to low fat content, lack of acid development, overheating during cooking, lack of moisture and excessive salt content.

ii) Crumbly Body: Crumbly body is characterized by the falling apart of cheese when sliced, by difficulty in removing a plug and by the breaking of the cheese into pieces crumbs when crushed between the thumb and fingers. This lack of cohesion is apparent through the whole cheese, it is not limited to surfaces of the curd particles which make up the cheese Crumbly cheese usually feels firm before breaking. It shatters with snap like breaking of chalk.

iii) Curdy Body: Curdy body is natural in fresh cheese, it is rightly regarded as a defect only when persists beyond about 30 days. Curdy cheese when broken apart reveals the size and shape of the original curd particles after salting. When pressed in the finger it feels elastic, firm and somewhat like the particles of the curd at the time of salting. It can not be worked together in the fingers after it has once been broken apart.It may be caused by low moisture content which delays curing, lack of proper acid development, lack of proper cheddaring in the vat before milling, addition of excessive amount of salt or low temperature storage.

iv) Mealy Body: This characteristic appears when cheese is crushed and rubbed between the thumb and fingers ,the structure of the curd looks and feels rough.The characteristic is the opposite of the waxy, smooth desired in normal cheese.Mealy body can be most readily detected after the curdy characteristics of the cheese have been fully disappeared, it is actually apparent during the first week of curing but is not so easily discovered. It persists throughout the life of cheese.It is mainly caused by excessive acidity. It may be regarded as a stage of disintegration of crumbly cheese. Mealy body in cheese can be eliminated in future lots by observing the preventions and remedies for excessive acidity.

v) Pasty: Cheese with pasty body is soft in consistency when pressed and rubbed between the fingers, it quickly becomes sticky and clings to the fingers. Pasty body in cheese becomes apparent as soon as the curdy characteristics disappear. The defect is caused by excessive moisture.

 iii Texture

Texture is the term used to describe the manner of union of the particles of cheese.If there are few openings or none at all between the particles, then the texture is said to be close or solid. If there are spaces between the particles or if there are voids or openings in the body, then the texture is said to be open.

i) Gas Production: Open texture and slits in Cheddar have been attributed to the growth of obligate and facultative heterofermentative lactobacilli.Fermentation of residual lactose and galactose, resulting in the production of CO2, is associated with this defect. Slow starter activity and a high level of residual lactose in the curd are the main causes. Late gas-blowing in Cheddar is associated with contamination of the cheese milk with Clostridium tyrobutyricum.

ii) Colour defects: Colour plays an important role in the consumer acceptability of Cheddar and can influence grading. Bleaching of Cheddar is sometimes observed shortly after manufacture. Localized areas of high acid production with whey entrapment between curd particles can cause bleaching during the early stages of maturation. This effect diminishes as the cheese matures and the pH increases. Colour defects ranging from pink to mud-brown have been observed sporadically in both annatto-coloured and white mature Cheddar.

iii) Mould Growth: Most commercially produced Cheddar is vacuum-packaged and as moulds require oxygen to grow and sporulate, they are found where pockets of air exists between the cheese surface and packaging. Growth is limited by the amount of limited oxygen.