Yoghurt is produced when milk comes into contact with certain strains of bacteria and is fermented.
How is yoghurt made
Originally yoghurt was simply milk that was fermented by bacteria that contaminated it. The commercial strains we buy off the shelves of supermarkets are pasteurised to kill off any naturally resident bacteria. Other beneficial bacteria are then added in later as a "starter culture". Commercial yoghurt may also contain added sugar, stabilisers, fruit and flavours.
On arrival at the processing plant, milk destined to become yoghurt has some fat removed by centrifugation. Then to make it more solid, water is evaporated off and milk powder may be added. This enriches the protein content of the mix, with casein being one of the major proteins. The casien helps the mix to become thicker in consistency(1). Stabilsers such as gelatin, pectin, agar and starch may also be added in at this stage to make the yoghurt mix smoother.
The mix is then pastueurised by heating it, typically to between 85-95C, which kills any bacteria present. This also denatures the whey proteins, most of which are removed in the case of Greek yoghurt(2). It is then homogenised, which involves passing it through very small holes to break up the fat globules in it. This results in fats being spread evenly throughout the milk.
The yoghurt mix is then cooled to between 43-46C, and a starter culture of bacteria is placed into it to begin fermenting the lactose (a sugar naturally present in milk), into lactic acid. Various other chemicals, such as acetaldehyde are also produced, which contibute to the aroma of therefore taste of yoghurt(3). The lactic acid is responsible for the sour taste of the yoghurt.
Greek yoghurt is strained to remove the whey, which contains a few proteins, minerals and plenty of lactose. This means that Greek yoghurt is more easily tolerated by those with a sensitivity to lactose.
Healthy probiotic yoghurt
Most yoghurts, irrespective of their labelling, contain significant quantites of live bacteria and are thus probiotic.
The bacteria they contain are able to improve the quality of the bacteria in our intestines. This is associated with improved digestion. Some studies show improvement in recovery from H. Pylori infection when using probiotic strains of bacteria such as B. infantis, while a number of other studies have shown improvements in people with irritable bowel syndrome (IBS), mainly by reducing levels of abdominal pain and bloating(4).
Heart and bone health
Yoghurt is a major source of vitamin K2 and calcium. Vitamin K2 (menaquinone) is produced by the bacterial fermentation that is used in yoghurt production. Together menaquinone and calcium help prevent both osteoporosis and heart disease.
There are links between reduced rates of lower respiratory tract infection and regular consumption of probiotics, such as those found in yoghurt(5). This is not a surprise as the bacteria present in yoghurt stimulate our immune system and reduce levels of inflammation.
One of the little known facts about flavoured yoghurts is just how much sugar and sweeteners they can contain. Here is a breakdown from my local supermarket.
|Waitrose Essential low fat||6.9||2.9||6.1||no|
|Waitrose Essential full fat||6.5||10.0||4.5||no|
|Rachel's Vanilla low fat||12.4||1.8||4.4||no|
|Onken Strawberry low fat||12.8||0.2||4.5||no|
|Rachel's Honey full fat||12.7||7.5||3.3||no|
|Muller light Vanilla low fat||6.8||0.1||4.3||aspartame|
|Danone Activia Strawberry low fat||10||0.1||4.8||acesulfameK and sucralose|
You are best off avoiding artificial sweeteners in yoghurt. While xylitol and stevia may be reasonably healthy, other more common sweeteners have not been shown to reduce weight in obese people. This is partly due to their ability to persuade the brain to want more food(6). They also can predispose to a range of other metabolic illnesses, including type 2 diabetes. Some of the biggest names in yoghurt manufacturing use artificial sweeteners.
The level of sugar in flavoured yoghurts comes in consistently at a hefty 12-13%. That is a lot of sugar. A flavoured yoghurt is pretty much the same as eating a dessert or sweet. It is not a health food. Unflavoured yoghurts, with around 6-7% sugar are much kinder to your waistline.
Yakult, which has an image as a health food tops the lists with 14.2-17.2% sugar depending on which product you look at. It has virtually no fat. If anyone thinks they will loose weight drinking this they are sorely misguided. Sugar is easily converted to fat in a sedentary body.
Often low fat is associated with the addition of a lot of chemical nasties. In the case of yoghurt this is not always the case. In some varieties the fat is skimmed off and qualities lost by removal of the fat are often compensated for by the addition of thickening agents. These include guar gum, pectin, starch and locust bean gum. In general they are healthy enough and no cause for concern. Therefore low fat yoghurt can be a reasonable choice if you want to restrict your fat intake. However a large number of low fat yoghurts such as Danone and Muller light do contain sweeteners and I would not advise you use these.
Greek yoghurts generally contain more fat than set yoghurts. While a full fat Greek yoghurt may contain between 8-10% fat a natural set yoghurt will typically contain 3-4% fat.
I'm a big fan of yoghurt, but I always encourage my clients to consume plain yoghurt and not the flavoured varieties. That is due to the excessive amount of sugar in flavoured varietes. I'd also advise you to avoid any varieties that contain sweeteners.
The potential benefits of regular yoghurt consumption are impressive. Better bowel health and reduced risk of chest infection along with stronger bones over the long term.