Most Brits have a pint of milk or two in their fridge - after all, the staple ingredient is essential to make tea, coffee and to whip up a lovely breakfast too. However, it turns out we may have been storing it wrong for years, and it's causing the product to turn sour.

Milk brand Kalona SuperNatural recently shared an ultimate food storage hack to help people make the most of their milk. While it's something you may never think about, where you place it in the fridge could actually be having a big impact on how long it lasts and stays fresh.

In a video shared on TikTok, the milk brand told people they're storing their milk "wrong", as it shouldn't be placed in the fridge door. Instead, it should be stored at the back of the fridge for a very important reason.

Alongside the video, guidance said: "Our number one tip is to keep your dairy products in a sealed container in the back of the fridge. Why lay it on its side?

"Well, for those of you who don't enjoy the cream top, this is a great way to stop the cream top from plugging to the top of the bottle. This also makes the cream layer thinner, making it easier to mix."

According to experts, the best place to store milk in the refrigerator is on the lower shelf, towards the back. It should be kept away from the fridge door.

This is because it's best stored in the coldest part of the fridge, as this will enable the milk to stay chilled and fresher for longer. The refrigerator door is the warmest area and is therefore not suitable for storing milk.

Generally, the lower shelves are considered the coldest part of the refrigerator, which means it offers the most consistent temperature for milk. When you place milk on the back of the shelf, and away from the door, this will limit temperature fluctuations caused by opening and closing the refrigerator.

The refrigerator door experiences the most temperature changes due to the action of opening and closing. When you think about it, it's easy to see how this can cause milk to spoil faster.

When storing milk, it's also important to keep milk containers tightly sealed to prevent odours from other foods from contaminating the milk. You should also avoid any spills.

What causes milk to turn sour?

Bacterial fermentation usually causes milk to turn sour, specifically the action of lactic acid bacteria, which converts lactose (milk sugar) into lactic acid. This process leads to lowering the milk's pH, causing it to taste sour and eventually leading it to curdle.

Milk naturally comprises of lactose, a sugar. Certain bacteria, such as lactobacillus and streptococcus thermophilus, consume lactose as a source of energy. As these bacteria metabolise lactose, they create lactic acid as a byproduct.

The buildup of lactic acid lowers the pH of the milk, which causes it to become more acidic. This then impacts the milk proteins, particularly casein, and causes them to coagulate and clump together, which results in milk curdling.

It's the increased acidity that gives soured milk its distinct sour taste and unpleasant smell, but there are ways you can avoid this happening. If you store your milk correctly, you should be able to prevent the problem.

However, it should be noted that factors such as temperature and contamination can also speed up the souring process. Higher temperatures encourage bacterial growth, and this can cause spoilage.