Why Does Milk Turn Sour?
Milk is excellent for quenching the thirst, and provides the body with practically all the necessary elements required for proper growth and developmental. 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:
- macro-elements (calcium, magnesium, fluorine, sodium, phosphorous, iodine, chlorine, sulfur etc.);
- microelectronics (iron, copper, zinc, iodine, fluorine, silicon, chromium etc.);
- proteins (albumin, globulin);
- vitamins (А, D, E,K, B);
- enzymes (lactose);
- The quantity of the various elements depends on the origin of the milk.
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.
Good Bacteria & Bad Bacteria
Milk contains bacteria. There are good bacteria and bad bacteria. Good bacteria are useful and bad bacteria are harmful. The bacteria that live in sour or old milk should be avoided. Milk also contains a type of natural sugar called “lactose”. The bacteria use lactose (sugar type) as an energy source to produce more bacteria. When this bacteria uses lactose to reproduce, it changes the “lactose sugar” into “lactose acid” which is sour in taste. Hence the milk curdles, becomes bad and sour, and is no better for use.
What is Putrefaction?
There is also another type of bacteria that can grow in milk. It makes protein derivatives that cause bad smell and milk is no better for use. The milk can also mold if air is available. This is called putrefaction.
The Speed Of Souring Is Affected By:
- Temperature – the higher it is, the greater the souring effect;
- 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.
- 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 electromagnetically impulses.
- Specific Bacteria – Milk contains a sugar called lactose. It also contains harmless bacteria called lactose bacillus, which uses lactose for energy and creates lactic acid as a by-product. It is the lactic acid which makes milk taste sour. Pasteurizing milk kills off harmful bacteria and greatly reduces the number of lactose bacillus ensuring that milk will last up to three weeks in a fridge. Lactose bacillus is a very useful bacterium as the acidic conditions it creates makes a milk protein called casein turn to curd. Without curd we would not have dairy food products like cheese.
By the way, you can do a very easy experimenter on find the protein in your favorite milk.
How Are Fermented Milk Products Beneficial (Harmful)?
The Benefits 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 firework 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?
Tips & Precautions to Keep Milk Fresh:
It's easy to achieve the best conditions to keep milk fresh for as long as possible simply by applying some basic principles. Here are some handy tips and tricks to get the most from your milk:
At The Supermarket:
When shopping, pick up the milk last so it doesn’t warm up while you fill your basket. Refrigerate at a temperature of between 0 °C and 4 °C as soon as possible after purchase.
Check the milk's best before date and choose the product with the furthest date.
At Home: How to Store Milk?
- Once opened, milk is safe to consume for up to 3 days. This is why it is better to buy smaller amounts more often rather than keeping larger containers open in the refrigerator for too long.
- Remember to open new milk containers in the same order in which you bought them. First in the fridge, first out.
- Keep milk containers closed and stored away from strong-smelling food items in the fridge—the milk can pick up these odours.
- Store milk on refrigerator shelves where it is cooler, rather than in the refrigerator doors.
- Whenever possible, leave milk in its original container to safeguard its flavour and nutritional value.
- Avoid exposing milk to light, as light destroys certain vitamins, such as vitamin D and riboflavin.
- To avoid spoilage, do not return unused milk from a serving pitcher to the original container.
- UHT and canned milk found in the non-refrigerated aisle are perishable once opened. Opened UHT and canned milk must therefore be refrigerated. After opening canned milk, immediately transfer any unused portions to a clean, opaque and airtight container. These milk products should be used within 3 days of opening.
- If stored in a cool, dry place, powdered milk will keep for up to 6 months. Once the package is opened, it should be used within 1 month. After being reconstituted, it should be stored and treated in the same way as regular fluid milk, meaning it should be refrigerated and used within 3 days.
- Milk can be frozen for up to 6 weeks without any impact on its flavour and nutritional value; however, upon thawing, it can separate and lose its smooth texture. Partly skimmed and skim milk freeze better than whole milk (3.25%). Thaw milk in the fridge. If the milk separates upon thawing, beat it with an electric mixer or an immersion blender with the whip attachment.
- Leftover evaporated milk can be frozen in an airtight container for up to 6 weeks with no adverse effects.
- If you freeze foods such as soups or stews, add the milk after you reheat the thawed food.
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”.