The external characteristics of food products contribute to the overall appearance of a product.
Jam with dry surface is not acceptable whereas a jelly with a glossy surface is rated high. Interior appearance can also be evaluated by looking at the internal colour, apparent abnormalities on the inner portions of the product etc. For example lumps in a sweet burfi or a jam which are not desirable can be judged by the eye.
Sight plays an important role in the assessment of the lightness of foods like the dhokla, cakes and idli. Additionally it can perceive the size, shape of the foods and of similar characteristics such as transparency, opaqueness, turbidity, dullness and gloss by the organs of sight.
The freshness of a fruit can be ascertained by observing the freshness of skin or peel. Spoiled bread can be identified by observing fungal growth on the surface
Infestation with insects can be found out in brinjal by the appearance of black spots on it. Completeness of cooking can be judged by appearance in products like meat and rice.
Colour of a food can be considered as a good indicator of the quality in addition to giving pleasure. Ripeness of fruits like banana, tomato, mango, guava, papaya and plum can be assessed by the colour. The colour of the biscuit is used for its doneness. The strength of coffee and tea is judged in part by the colour of the beverages. The colour of roast beef is used as an index to doneness. Toast, dosa, and chapathi which are too brown are likely to be rejected in anticipation of scorched bitter taste.
Flavor is not a single entity, but it is comprised of odor and taste.
Odour: The sensation that results when olfactory receptors in the nose are stimulated by particular chemicals in gaseous form. The main olfactory system detects volatile, airborne substances, while the accessory olfactory system senses fluid-phase stimuli.
An odour is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans perceive by the sense of olfaction. The odour of food contributes greatly to the pleasure of eating. A substance which produces odour must be volatile and the molecules of the substance must come in contact with receptors in the epithelium of the olfactory organ. Human olfactory sense has the capacity to distinguish about 16 million odours.
Aroma is able to penetrate even beyond the visual range when strong chemical compounds are present in a food; an example is cut mango fruit and pulp. In mango fruit, more than 285 different aroma volatile compounds have been reported which include 7 acids, 55 alcohols, 31 aldehydes, 26 ketones, 14 lactones, 74 esters, 69 hydrocarbons, and 9 other compounds.
The volatility of aromas is related to the temperature of the food. High temperatures tend to volatilise aromatic compounds, making them quite apparent for judging; cool or cold temperatures inhibit volatilisation.