Written by Raymond Nakamura
Once upon a time (before the Internet), Raymond earned his doctorate studying the hydrodynamics of sand dollars. Nowadays he rents his brain at raymondsbrain.com for writing, cartooning, and thinking, when he is not washing the dishes, walking the dog, or helping his daughter with homework. Follow him on Twitter @raymondsbrain.


Thanks to bacteria, we can enjoy yogurt

Created date

Sunday, May 22, 2016 - 7:00am

Ever Wonder About Yogurt?

At breakfast one morning, I read the label of my container of plain yogurt and wondered how partly skimmed milk, milk protein and bacterial cultures could result in what I was eating. Here's what I found out about these ingredients.

Bacterial Cultures

To be called yogurt, a product is supposed to contain Lactobacillus bulgaricus and Streptococcus thermophilus bacteriaThese are nice, probiotic bacteria that are supposed to be good for your intestines and, in some cases, already live there. In general, these bacteria produce lactase, an enzyme that breaks down lactose, the milk sugar. The fermentation of lactose results in lactic acid. Lactic acid, as the name suggests, lowers pH and gives yogurt that tangy taste. The lower pH causes the protein molecules to denature or unravel, which thickens the yogurt. Some of what makes yogurt good is like what happens when milk goes bad. Different brands use different bacteria, which can affect flavour and other properties of the yogurt. Mine listed Bifidobacterium lactisLactobacillus acidophilus and Lactobacillus casei

If the yogurt has live bacteria in it, they can still survive being eaten by humans and continue to help break down the lactose. This is why people who might be lactose intolerant can eat yogurt, although there's still some lactose in it. My yogurt container claimed that it contained "more than 1 billion probiotic bacteria per serving that contribute to a healthy intestinal flora." That sounds good, but the effectiveness of yogurt to improve your intestines is tricky when you consider that you could have tens of trillions of microbes in your gut.

Partly skimmed milk

Milk is the main ingredient of yogurt, and by eating yogurt you get most of its nutrients, like calcium. Many sites have instructions for making yogurt at home and experimenting with how you make it. Commercial yogurt comes with different amounts of fat. Mine said 2%. Fat free yogurt might not be as thick, but the fat does not seem to be integral to the key processes in making yogurt. Mostly I choose by what's on sale. 

Milk Protein

Adding milk protein is not necessary to make yogurt but is included in the commercial process to make it thicker. The milk gets heated to kill off unwanted bacteria. Keeping the milk above 90°C (195°F) causes lactoglobulin, one of the main proteins in milk, to denature. This adds to the thickness of the yogurt. As the culture becomes acidic because of bacterial action, the proteins form a gelGreek yogurt strains out the liquidy whey and so even if fat free, will be thicker.

This is just a taste of all that goes into yogurt. It's a lot to digest. If you have any tips on making yogurt please leave them in the comments and maybe one day I'll try it myself.


Still feeling curious? Keep reading! Have you ever wondered about expiry dates on food or why we put fluoride on our teeth

 

Comments

I make yoghurt like my father

I make yoghurt like my father used to. Bring the milk to a boil to kill off all unwanted bacteria. Leave to cool until you can hold your little finger in it. (43-49 deg C ideally). Stir in live yoghurt (say 1 cup to 3-4 pints) and stir well. Cover the container, place a hot water bottle next to it,wrap in a blanket or sleeping bag and leave overnight. Perfect every time. I strain half of it to make a Greek-style yoghurt and use the resultant whey instead of buttermilk to make soda bread....

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