Determination of smell, taste and crunch.
20 g of flour pour out to the clean paper, warm with respiration and is investigated smell. For strengthening the sensation of smell they transfer to beaker flour, they douse by hot water of 60°C, and then they pour water and determine it smelled the tested test. The smell of flour must be not musty, not moldy, without any outside smells.
Taste and crunch are determined organoleptical by the chewing of flour. Flour of normal quality must have fresh, weakly sweetish taste. Crunch on the teeth with the chewing there must not be perceived.
Slightly acid aftertaste indicates to stale flour, acid or bitter - to the bad quality. Bitterest taste gives to flour the admixture of wormwood and some other cultures.
Determination of color.
The color is determined organoleptically on the standard: the test of flour, poured on the bright sheet of paper, is examined with the day scattered light or with the sufficiently bright artificial lighting.
Determination of humidity.
The standard method of the determination of humidity content of flour is the desiccation of the hinges quantities of flour in the electrical cabinet drier СЭШ-1.
Preliminarily they dry and calibrate metallic weighing bottles with the diameter of 48 mm and with the height of 20 mm with an accuracy to of 0,01 g. From the selected and thoroughly mixed test of flour into the weighing bottles they weigh out on the counterbalances of the hinge quantity of flour near 5 g with an accuracy to of 0,01 g.
Cabinet drier preliminarily they heat to 130°C and then 10 weighing bottles with the hinges quantities of flour rapidly are placed in it, placing them on the taken covers. Desiccation in the cabinet is conducted during 40 min. Thermometer bulb must be located at a distance by 10 mm from the upper edge of weighing bottles.
After 40 min the weighing bottles with the hinges quantities take out from the cabinet by crucible tongs, they cap and transfer into the exsiccate to the complete cooling approximately on 20-25 min.
After cooling of weighing bottle they weigh also by the difference between the mass of the hinge quantity before and after of desiccation, initial hinge quantity referred to the mass, humidity W is determined, expressing it in %. Calculation they conduct with accuracy to 0, 1 according to the formula:
(a - b)
W= ------------ . 100
a
where: a - mass of the hinge quantity of flour to the desiccation, g;
b - mass of the hinge quantity of flour after desiccation, g.
Arithmetic mean of two parallel determinations they assume as the index of the humidity of the tested test of flour.
Materials and the equipment
- Counterbalances, Erlenmeyer flask by the capacity of 100-150 ml, distilled water,
1%- foot alcoholic solution of phenolphthalein, 0, 1 n by the solution of alkali.
Method of performance
Determination of acid.
This index characterizes first of all the degree of the freshness of flour.
Take 5 g of flour, weighed on the counterbalances. They pour out into the Erlenmeyer flask by the capacity of 100-150 ml with the preliminarily filled into it distilled water in a quantity of 50 ml. Contents of flask they shake up during approximately 3 min so that entire flour would be moistened well by water. The adhered to the walls particles of flour, as far as possible, they wash off by the distilled water. Then they add 5 drops 1%- foot alcoholic solution of phenolphthalein and titrate 0,1 n by the solution of alkali before obtaining of the weakly-pink dyeing, which does not disappear during 1 min.
Acidity X determines with accuracy to 0, 1° according to the formula:
N • 100
X=----------- K
A • 10
where N - volume of the alkali, spent for the titration of 100 g of flour, ml;
A - mass of hinge quantity, g;
K - correction factor for the caption of 0,1 n of alkali;
10 - conversion factor of 0, 1 n of the solution of alkali to 1 n.
With the hinge quantity accurately of 5 g the value of the acidity of flour is obtained by the multiplication of the spent number of milliliters of 0, 1 n of alkali by 2 and by the correction factor for the caption of alkali.
Note: For the expression of acidity in the degrees a quantity of spent by 0, 1 n alkali they multiply by 2.
Control questions
1. What organoleptic indexes are characteristic for the flour?
2. What does characterize the acidity of alkali?
3. What units are expressed the index of acidity?
Laboratory work #7