Baking colour

Natural clays are coloured due to pollutions of the clay minerals. After baking the colour is strongly affected by the Ca/Fe ratio. When the baking colour is not white, this is caused by metal ions with d-valence electrons (see glazings in the paragraph Fine ceramics and baking colour in the paragraph Coarse ceramics). 

Generally said, the iron content is responsible for the red firing colour and the calcium content for the yellow colour. When the iron content is low and enough aluminium oxide is present, the free iron(III) oxide will bind with the silicates to form yellow compounds. Table 11.2.1 lists the baking colour as a function of the proportion of the iron(III) oxide, aluminium oxide and calcium oxide masses. 

In addition, the various iron oxides interreact and the atmosphere and temperature determine which oxide is preferably formed and consequently which baking colour the product will have (in calcium-poor clay ) ... 

These analyses are mainly performed on natural raw materials, notably on clay. The user of this clay is always interested in the mass percentage Fe, Ca and humus and in the mass percentage loam, fine sand and coarse sand. The contents of iron and calcium affect the baking colour and other contents are of influence on the properties of the mass as far as moulding and drying and firing behaviours are concerned. Furthermore we have learnt from the chapter on clay that this material may contain many more components which sometimes also need to be determined, for instance for environmental reasons. 

Sanding is carried out at this stage and, after clean-up, the final colour or top-coat is applied. There is some variation in the resin chemistry used. Alkyds crosslinked with melamine-formaldehyde are widely used for non-metallic pigmentation. Metallics are usually based on acrylics for better durability. The acrylic may be thermoset with melamine-formaldehyde or a thermoplastic lacquer (plasticised copolymer of methyl methacrylate). A thickness of about 50ftm is applied and stoved for 20 min at 130°C (lacquers receive a bake-sand-bake process for a smoother appearance). 

Milk solids are normally used as either milk powder or sweetened condensed milk in food manufacturing. Skim milk solids are an essential part of toffees as well as contributing useful colour and Maillard reaction flavours to baked goods. 

The major use (60%) for coloured inorganic pigments, such as iron oxides, is in the construction materials industry. Here they are used to colour roof and flooring tiles, fibrous cement and mortar. Many inorganic pigments are used in coloured baking enamels for metal appliances. Chromium oxide is used in the refractory industry, not for its colour but because of its ability to improve the properties of bricks used in furnace linings. 

Color is important in all forms of potato products, boiled, baked, fried, and chipped. Where a limited number of broad classifications are used, as in some commercial processing situations, use is made of visual reference charts showing a limited range of colors. Such charts are available for French fiies (Munsell USDA Frozen French Fry Standard, X-Rite Right On Colour) and for potato chips (Colour Standards Reference Chart for Potato Chips, Snack Food Association). 

Saffron is used to colour and flavour food, the best known dishes being paella and the French fish soup bouillabaisse. There is also saffron bread, popular in the Balkans and Scandinavia, and saffron cake which is baked in Cornwall, England. Saffron has two natural chemi-... 

It is a bright yellow, crystalline powder, insoluble in water, and on account of its stability or inertness is used as an artists pigment. It is a very pure compound when prepared as indicated above, for neither iron nor nickel yields a corresponding derivative it is therefore valued for painting porcelain, because the blue colour produced on baking is correspondingly pure and beautiful. Furthermore, as has already been mentioned, the salt yields a valuable method of separating nickel from cobalt (see p. 24). 

Katin ka 2nd-3rd oblong, colouring like Hauszwetschke, 32 g steep, dwarfing susceptible if attack is severe pure baking plum, very high yield, plant close together, new cultivar... 

Ersinger 3rd oval, sharp flavour, skin reddish semi-vigorous, flat-branching only leaf symptoms fresh consumption and baking, thin sometimes, quickly goes soft, weak point colouring... 

Julia 4th flattened oval shape, colour like Hauszwetschke, tart-aromatic vigorous, steep only leaf symptoms, few fruit symptoms late cropping, appreciated for baking, also fresh consumption... 

Enzymes find commercial use in detergents, leather processing, baking, brewing, cheese mannfactnre, fruit juice processing, dairy production, animal feed, wine making and textiles. A wide variety of different enzymes finds use in textile areas as shown in Table 17.1. This chapter will focns on cellulases, which are enzymes that catalyse the hydrolysis of the cellnlose polymer. Except for the peroxidases, which are used to improve colour fastness and are described in Chapter 13, all the other types of enzymes are nsed for preparation processes and therefore not inclnded in this discussion. 

Overall, food quality may be considered in terms of taste, textme, mouthfeel and other sensorial attributes or in terms of macro- and micronutrient content. For any concept of visual quality, colour acts as a very useful and intuitive indicator. Colour can be assessed at various times during the lifetime of a food product - from raw materials, e.g., the quality of flour for baking, through processing, e.g., monitoring roasting of coffee beans, and at the end point where a finished product needs to be confirmed as suitable for its designed purpose,... 

Table 14.1 Effect of baking time on breakfast cereal colour...

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