Why does milk go sour?

There is only one prod­uct in the world which no species of mam­mal can sur­vive with­out. Milk. Whether it’s a baby hu­man be­ing, deer, kit­ten or ele­phant, the first thing they will eat in their lives is their moth­er’s milk.

The ben­e­fit of this prod­uct was proved in An­cient Greece. For ex­am­ple, Hip­pocrates pre­scribed it for pa­tients as a cough medicine, while the renowned Rus­sian sci­en­tist Ivan Pavlov called milk a food cre­at­ed by na­ture.

Milk is ex­cel­lent for quench­ing the thirst, and pro­vides the body with prac­ti­cal­ly all the nec­es­sary el­e­ments re­quired for prop­er growth and de­vel­op­ment. Be­sides its ben­e­fits, the prod­uct has a unique taste that is pleas­ing to both chil­dren and adults.

De­spite all of its nu­mer­ous ben­e­fi­cial prop­er­ties, milk has one se­ri­ous short­com­ing – it goes bad very quick­ly. Why does it turn sour? Is this a bad thing or a good thing? How can we keep it fresh? We will try to an­swer these ques­tions in this ar­ti­cle.

To start with, let’s see what milk is and what it con­sists of. Milk is a nour­ish­ing, mul­ti-com­po­nent liq­uid which is pro­duced by the mam­ma­ry glands for feed­ing ba­bies. Its com­po­si­tion in­cludes:

• macroele­ments (cal­ci­um, mag­ne­sium, flu­o­rine, sodi­um, phos­pho­rous, io­dine, chlo­rine, sul­fur etc.);

• mi­croele­ments (iron, cop­per, zinc, io­dine, flu­o­rine, sil­i­con, chromi­um etc.);

• fats;

• pro­teins (al­bu­min, glob­u­lin);

• vi­ta­mins (А, D, E,K, B);

• en­zymes (lac­tose);

• bac­te­ria.

The quan­ti­ty of the var­i­ous el­e­ments de­pends on the ori­gin of the milk.

Why does milk go sour?

As we can see from the com­po­si­tion, the lac­tic medi­um con­tains var­i­ous types of bac­te­ria. In nor­mal form they are not dan­ger­ous for the or­gan­ism, but over time (es­pe­cial­ly un­der the in­flu­ence of ac­cel­er­at­ing fac­tors) they start to mul­ti­ply, trans­form­ing lac­tose into lac­tic acid. As a re­sult, the acid­i­ty of the milk in­creas­es, which in its turn caus­es the pro­tein to fold and liq­uid to sep­a­rate into whey and a vis­cous mass.

The speed of sour­ing is af­fect­ed by:

1. tem­per­a­ture – the high­er it is, the greater the sour­ing ef­fect;

2. a dirty con­tain­er – the pres­ence of wa­ter, fat, dust etc. in the milk con­tain­er can dou­ble the speed of the time it takes milk to go sour.

3. the weath­er – if you put a milk jug on the win­dow sill dur­ing a storm, in the morn­ing you will have home-made ke­fir. Sci­en­tists can­not give a pre­cise ex­pla­na­tion of this process, but many be­lieve that it is caused by elec­tro­mag­net­ic im­puls­es.

4. spe­cif­ic bac­te­ria – spe­cial­ly cre­at­ed sub­stances de­signed for a quick­er and more ef­fec­tive change of milk into ben­e­fi­cial fer­ment­ed milk prod­ucts. They in­clude: ke­fir fun­gi (ke­fir), lac­tic yeast (yo­ghurts), pro­pi­onic bac­te­ria (cot­tage cheese) and lac­to­bacil­lus (boiled fer­ment­ed milk).

By the way, you can do a very easy ex­per­i­ment on find the pro­tein in your favourite milk.

How are fer­ment­ed milk prod­ucts ben­e­fi­cial (harm­ful)?

The ben­e­fit of fer­ment­ed milk:

Eas­i­ly di­gestible – whole milk is di­gest­ed by just 32%, while ke­fir or boiled fer­ment­ed milk is di­gest­ed by 91%.

The lac­tose helps to im­prove the func­tion­ing of the di­ges­tive sys­tem.

Lac­tic and bi­fidus bac­te­ria help the body to pro­tect the in­tes­tine from harm­ful micro­organ­isms.

The acidic medi­um helps to ab­sorb cal­ci­um bet­ter.

You can make ke­fir your­self. Just add a spoon­ful of sour cream to milk, or wait for it to go sour of its own ac­cord. Good milk will start to fer­ment af­ter be­ing kept in a warm place for just 8-12 hours. Dairy farms rig­or­ous­ly de­stroy all bac­te­ria ca­pa­ble of mul­ti­ply­ing be­fore pack­ag­ing milk in car­tons. They do this to ex­tend the shelf life of the prod­uct. This milk can be kept for a long time, but if it fer­ments it will ac­quire a bit­ter acidic taste, and may cause var­i­ous dis­eases.

How can we keep milk fresh? A few lit­tle tricks.

1. Only pour milk into a dry, clean con­tain­er (prefer­ably glass or ce­ram­ic).

2. ONLY wash milk con­tain­ers with cold wa­ter (hot wa­ter ac­cel­er­ates the fer­men­ta­tion process).

3. Keep milk away from oth­er smells and air.

4.Keep away from light (this caus­es vi­ta­mins to break down).

Ob­serve these sim­ple rules, and milk will keep your fam­i­ly hap­py for a long time to come. There’s a good rea­son that peo­ple say “Drink milk and you’ll be healthy”.