The order of performance of job. Required materials and ware: 1
Required materials and ware: 1. Cocoa powder and chocolate. 2. Sieve with wire-netting.
3. Crayon brush. 4. Pounder with pestle. 5. Refractometer. 6.Measuring glass or flask capacity 25,50 cm3, funnel, micropipette. 7. Picnometer on 25 cm3. 8. Paper filter, cotton, scalpel.
9. Technical balance. 10. Naphthalene monobromate or naphthalene monochloride.
1.Definition of organoleptic indicator cocoa powder and chocolate. At determining of organoleptic indicator of cocoa powder its taste and flavour are tested in drink, prepared in such a manner. Weigh out 4g of powder, add 6g ofgranulated sugar and 5cm3 of water or milk. After cooling it to 400 C determine it taste and flavour. Definition of cocoa powder suspension’ firmness determine also in drink. Suspension is considered firm, if during 2 min after brew there is no noticeable sludge.
Аt determining of organoleptic indicator of chocolate its outward, form, consistence, structure, taste and flavour are defined. By inspection of outward regard must be paid to condition of front surface, form, presence of defects. Consistence of chocolate must be firm, structure- homogeneous, for porous- honeycomb. Taste and flavour must be peculiar for chocolate.
2.Definition of degree of cocoa powder grinding. Method is founded on sifting product and weighing residue on the sieve. Sample of cocoa powder in quantity 5g, taken with accuracy 0,01g, sift on sieve with wire-netting 016, slightly shake and help with brush. Sifting lead till on list can be seen black particulate solids. On the end of sifting sieve with remains and brush weight. Degree of grinding in percentage calculate by formula Хизм=(m1-m2)·100%/m, where m1- mass of sieve with remains of studied product and brush, g; m2- mass of sieve with brush, g; m- sample of cocoa powder, g. Obtained data compare with norm.
3.Definition of fat mass fraction by refractometric method. Method is founded on pulling out fat from sample with the help of naphthalene monobromate and definition refraction index of solvent and solution of fat in solvent with the help of refractometer. Naphthalene monobromate well dissolves fat in the cold and have high rate of refraction, differ markedly from from refraction index of fat. On dissolving of fat by naphthalene monobromate refraction index decrease at amount, proportional amount of fat resolve.
Mass of solvent density is determined by picnometer and calculate by formula: p20= (m2-m)998,23/ m1-m,where m2-mass of picnometer with solvent, g; m1-mass of picnometer with water, g; m- mass of empty picnometer, g; 998,23- value water-mass density by 200C, kg/m3. Density of solvent is necessary to know in order to calculate exact volume of pipette.
Pipette by capacity 2cm3 is calibrated according to solvent, measuring by it corresponding volume of solvent and weighing it in measuring glass with an accuracy to 0,0015g. Discordance between parallel deliberations must be not above 0,005g. From three weighing take arithmetic average and calculate volume of pipette Vп by formula: Vп= m3 ·100/ p20,where m3-mass of solvent, according to volume of given pipette, g; p20 -density of solvent by 200C, kg/m3 .
At first determine refraction coefficient of solvent, applying on prism of refractometer 1-2 drops of it by temperature 200C. Then weigh out 0,5-1,5g well gritted product to the accuracy 0,001g . Mass of sample depends on content therein fat (tabla1).
The table1. Dependence mass sample from fat content
| Fat content, % | Sample,g |
| Above 30 | Not less than 0,5 |
| From 20 to 30 | 0,75 |
| From 10 to 20 | 1,00 |
| Below 10 | 1,50 |
Sample place in pounder, grind by pestle 2 min, then add with calibrated pipette 2cm3 of solvent and once more grind during 3 min. Mixture filter in measuring glass or test tube through paper filter during 30min. Filtrate mix by glass rod, apply on prism of refractometer by temperature 200C and count off refraction index.
Mass fraction of fat Хж in percentage terms calculate by formula:
Хж= Vр ·p20ж/1000· m·Кр/ Крж·100%, where
Vр- volume of solvent, taken for fat recovery,cm3;
p20ж- density of fat by 200С, kg/m3;
Кр- refraction coefficient of solvent;
Крж- refraction coefficient of fat solution in solvent;
m- sample of product.
Report on the work done fix in table 2.
Table 2. Quality factors of cocoa powder
| Factor | Norms | Factual evidence |
| Outward | ||
| Taste and flavour | ||
| Degree of grinding | ||
| Firmness of suspension | ||
| Fat content |
Control questions:
1. What does organoleptic analysis of products consist of?
2. How does mass of sample depend of fat content?
3. How is mass fraction of fat in cocoa powder determined?
4. Describe the process of getting cocoa powder and chocolate.
Laboratory work # 6