1. Examination of raw milk
Physical and chemical properties of raw milk

2. Examination of milk purity
During milking different contaminating materials may get into milk (epithelium, fur, feed etc) so it has to be filtered.
Dirt →indicate high microbial contamination
1.) Sedimentation test
Pour 1 litre milk, let it stand for 1 hour
flotation
sedimentation
2.) Filter test

3. Examination of milk density
The density of milk: is the mass of a certain volume of milk at 15oC (g/ml)
Quick method for testing milk alteration:
→watering ↓
→skimming ↑
Unit: Lactodensimeter degree, (oLd)
32oLd = 1,032 g/ml
Standard: 1,029-1,034 g/ml at 15oC
Instrument: dipping lactodensimeter combined with thermometer
Pour milk into a glass cylinder 
put the lactodensimeter into the milk
read results
it refers milk at 15oC
If warmer →dips more →lower result→ +0,2/oC
If colder →dips less →higher result → -0,2/oC
At least 5 hours after milking

4. Determination of freezing point
Most sensitive method for detecting foreign water in milk. Freezing point depends on the lactose content and salt concentration. (breed: - 0,540oC; holstein: - 0,528oC)
- 0,520oC or less
0,003-0,005oC changing in the temperature means 1% water
0,5-1% foreign water can be acceptable
It can be determined by cryoscope and an instrument with thermistor.

5. Determination of total solids
This method is used when the chemical content of milk is examined or when there is a suspicion of alteration.
Fat free total solids = solids-non-fat-content: 8,5 g/100cm3, 8,2 g/100g
1. Drying method : It means the remains of the milk after drying at 102+2oC until its weight will be constant.(g/100g)
Method:
We measure 30g of sand into a pot 
30 minutes in a drying box at 102+2oC
10g milk into the pot, (mix with sand)
102+2oC until its weight will be constant (check in every hour)

6. Determination of total solids
Infrared absorption method
Determination by calculation
a.) total solids
ts = 1,2*f + 2,665*( /d) g/100 cm3
b.) solids-non-fat-content 
snf = ts-f g/100 g 
c. calculation of solids-non-fat-content by Fleischmann table

7. Determination of protein content
Importance: as a quality parameters of milk (buying up price, cheese production, etc.)
The expected total protein content should be at least 3,3% (casein: 2,7%, albumin + globulin: 0,6%)
Kjeldahl-method: :
Classical method: accurate, but long procedure
Formoltitration by Schulz
Principal of the method: we bind the free amino groups of amphoter proteins in the milk with formaldehyde. Then we titrate the released carboxyl groups with alkaline and by the consumption of it we determine the protein content
Milk getting sour can give higher results.
Infrared absorption method and colour binding chemical reaction are also used

8. Detection of the potential acid degree
Potential acid degree: the whole amount of alkaline binding substances
Soxhlet-Henkel method
The acid degree by Soxhlet-Henkel of milk is (OSH): the required ml-s of NaOH solution of 0,25 M to neutralise 100 ml milk at the presence of phenolphtalein indicator
Standard acid degree of raw milk: 6,0 – 7,2 OSH
a, 50 ml milk
2 ml 2% alcoholic phenolphtalein indicator 
0,25 M NaOH (light pink colour)
 The used ml-s of NaOH x 2 = OSH of milk.
b, 20 ml milk
1 ml 2% alcoholic phenolphtalein indicator
0,1 M NaOH (light pink colour)

9. Determination of the actual acid degree (pH value):
The actual acid degree means the amount of the hydrogen ions of milk.
Standard pH value: 6,6 – 6,75
In case of mastitis: neutral or alkalic
Colostrum: a bit acidic
Indicator paper: informative but not accurate
Electrometric way with pH detecting instrument

10. Determination of freshness of the milk
Alcohol test:
Principal: when the milk is getting sour (the OSH is higher), or its content abnormal, the balance of the colloid system changes and the proteins by the effect of 68 %alcohol will be precipitated. (above 8 OSH)
2 ml milk
2 ml 68 % alcohol (60,5 mass%, at 20oC 0,894 density) 
mix together
In sour milk casein precipitate forming little flakes. There is a relationship between the fineness of the precipitate and the acid degree of the milk.
At higher temperature the precipitation is faster and rougher.

11. Determination of freshness of the milk
Boiling test
Principal: the casein precipitates by the effect of heat below a certain pH value.
5 cm3 milk in a test tube 
boiling in flame or in a water bath of 100oC for 2 minutes
Casein precipitates can be seen: +
Milk having 10 – 12 OSH or higher coagulates.
Because of high globulin-content of colostrum it can show this reaction too.!!!

12. Control of heat treatment of milk and milk product
The peroxidase and phosphatase enzymes presented in the milk get decomposed at certain temperature and time.
Long lasting pasteurisation: 62-65oC, 30 minutes
Quick pasteurisation: 72-78oC, 15-40s
Flash pasteurisation: oC
Detection of phosphatase
Principle: In milk non heat treated or heat treated but mixed with raw milk or milk product phosphatase can be found and it releases 3,3-dimethyl-phenolphtalein from 3,3-dimethyl-phenolphtalein-hydrogen-phosphate which gives PURPLE colour in presence of alkaline. 5 ml milk
2 ml phosphatase reagent 
15 minutes, water bath of 37oC
0,5 ml 1 M KOH or NaOHsolution
Consideration: Purple colour presence of phosphatase  raw milk or pasteurised milk mixed with 2-5% raw milk
No colour changing  the heat treatment inactivated phosphatase

13. Detection of peroxidase by the Storch test
Principle: The peroxidase is sensitive temperature above 80oC. The enzyme release atomic oxygen from H2O2 which oxydates N,N-dimethyl-1,4-phenylen-diamine-hydrochlorid to bluish grey compound.
6 ml milk
1 drop 1-3% H2O2 solution (H2O2  H2O + ’O’) (Storch 1)
2 drop 2%paraphenylen-diamine solution (Storch 2) 
Consideration: after a few minutes it turns to a bluish grey colour  insufficient heat treatment
Keeps it original white colour  appropriate heat treatment

14. Fast microbiological methods
Reductase-tests
Indicator material + microbe-dehydrogenase enzym→ colour changes
Raw milk: only in degrees, not accurate result
Contaminating microflore decrease the redox potencial of the media →redox indicators → colour changes

15. Fast microbiological methods
The methylene blue reduction test
is based on the fact that the color imparted to milk by the addition of a dye such as methylene blue will disappear more or less quickly. The removal of the oxygen from milk and the formation of reducing substances during bacterial metabolism causes the color to disappear.
Though certain species of bacteria have considerably more influence than others, it is generally assumed that the greater the number of bacteria in milk, the quicker will the oxygen be consumed, and in turn the sooner will the color disappear. Thus, the time of reduction is taken as a measure of the number of organisms in milk although actually it is likely that it is more truly a measure of the total metabolic reactions proceeding at the cell surface of the bacteria.

16. Fast microbiological methods
The resazurin test is conducted similar to the methylene blue reduction test with the judgement of quality based either on the color produced after a stated period of incubation or on the time required to reduce the dye to a given end-point.