You know, that microbes transform the components of the milk, especially milk sugar and cheesecake, which be it directly, or under the influence of lactic acid it loses its original properties, especially in terms of solubility. In practice, it is these changes that determine the usefulness of milk. Let's just imagine such a case, that part of the cheesecake in the form of cottage cheese will also get into the rennet cheese, thus the material is matured differently than paracasein.
The chemical transformation of cheesecake can take place in milk under the influence.
1. Lactic acid, which as it forms, it gradually takes away the calcium from the cheesecake and makes it less and less puffed up to a point, in which the milk can no longer stand boiling. Eventually, the milk clots on its own. It is a lactic acid fermentation.
2. Rennet enzyme secreted by certain microorganisms, e.g. from the hay group, the milk forms a completely sweet clot. It is rennet fermentation.
3. Rennet ferment and lactic acid simultaneously produced by some bacteria, e.g. kernels are replaced. Then the milk solidifies at a lower acidity than under pure lactic acid fermentation. This is called. mixed fermentation, that is, acid-rennet.
We can see here certain fermentation trends that are of great importance in practice. Thus, practical goals require not only knowledge of the degree, but also the direction of changes taking place in milk.
Attempted by boiling. It is an attempt almost as simple and as old as humanity, and always useful, consisting in boiling a small amount of the tested milk. Sweet milk will not boil over (the cheesecake does not fall off then) and will not burn at the bottom of the pan. In milk having about 27 ° C acidity according to Marshall, the cheesecake is curled into fine lumps, in a more acidic one - it coagulates and separates from the whey.
The alcohol test is more sensitive and comfortable than the previous one. A small amount is put into the test tube (1 do 2 cm3) milk and as much alcohol 68 interest (not denatured) and mixes. The alcohol test detects even low levels of acidity as well as the onset of rennet fermentation. The further the acid fermentation proceeded, rennet or mixed, the larger flocs or flakes separate the cheesecake.
The alcohol test requires great practice in assessing the milk according to the particle size of the precipitated cheesecake. It does show a degree, but not the kind of milk breakdown.
Alizarol test - more specifically alcohol-alizarin test. Morres changed the old alizarin test by combining it with the alcohol one. Its advantage is this, that it quickly and easily indicates the approximate degree and type of milk breakdown, and, moreover, a defective composition of mineral salts.
Alizarin is an indicator of the reaction as well as e.g.. fe-nolooftaleina. Acids color it yellow, rules for violet. Alkaline solution colored with alizarin violet turns red after weak acidification, after further gradual addition of acid to pink, finally yellow. There are also various transitional colors on this scale. Thus, we can infer an alkaline and acidic reaction from the color.
Normal chemically fresh milk turns violet red under the influence of alizarin, similar to the color of clover. Deviations from this color are indicative of the changes that have taken place. If, in addition to changes in color, the size of the alcohol precipitated cheesecake particles is taken into account, then one can draw a conclusion
about that, how strong and in what direction the fermentation took place in milk. In the case of rennet fermentation, the color of fresh milk is only slightly darker (cherry), with a strong precipitation of the cheesecake. Mixed fermentation occurs more often than rennet fermentation itself, which you recognize after it, that the cheesecake flakes are larger than it would fall out of color. Alkaline milk, in the cheese room completely useless, turns violet.
Alizarol is a solution 0,55 g of alizarin per liter 68 alcohol percentage. It is best to dissolve alizarin in hot alcohol or sodium hydroxide solution, taking on 1,5 g alizaryny 3 cm³ of 1-n sodium hydroxide solution.
For the sake of economy, you can also use denatured alcohol as a solvent, however, this requires previous testing due to the volatility of contaminants.
| Acidity in Marshall degrees | Barwa | The degree of precipitation of the cheesecake during acid fermentation (not rennet) |
| 16 | violet red | no precipitation |
| 18 | pale red | no precipitation or fine |
| traces of cheesecake | ||
| 20 | brown-red | fine flakes |
| 22 | red-brown | fine flakes |
| 24 | brown | thick petals |
| 26 | yellow-brown | very thick petals |
| 31 | brownish-yellow | very thick petals |
| 36 | yellow | very thick petals |
| 45 | light yellow | very thick petals |
Performing the alizarol test is the same as the alcohol test, namely, equal amounts of milk and ali-scrub are put into the test tube, e.g. 2 : 2 cm3. The tube is shaken lightly and the color of the contents and the size of the precipitated cheesecake flakes are observed. The color indicates the direction of fermentation, and the size of the flakes of the precipitated cheesecake - the degree of decomposition as in the normal alcohol test, which alizarol is much preferable to.
Determination of acidity by titration with lyes. This test allows us to find more than just presence, but also the amount of acid in the milk. It is about this, that some phenolphthalein is added to the milk as an indicator and gradually as much of the standard solution of sodium or potassium lye, until all the acid has neutralized and a little excess lye is formed. This moment is indicated by phenolphthalein, which turns pink with a slight excess of lye.