Thick and creamy Greek style yoghurt is very trendy these days. However most of the brands of Greek yoghurt available in the US are not made in Greece! Why pay extra for Greek yoghurt that doesn't really come from Greece ? With a few kitchen utensils and some plain yoghurt it's easy enough to make Greek style yoghurt at home.
What is yoghurt?
Yoghurt is made from milk that is allowed to sit, incubate or ferment with certain 'friendly' bacteria. The bacteria use the sugar (lactose) in the milk and convert it to lactic acid. The main protein in milk, casein, doesn't stay dissolved in the acidic environment that results as the lactic acid builds up. The casein falls out of the solution (precipitates), giving good yoghurt its creamy semisolid texture. Because most of the lactose is converted to lactic acid, yoghurt can often be eaten by those with lactose intolerance. It also keeps better since other harmful bacteria don't readily grow in that acidic environment.
Many commercial yoghurts are thickened with pectin, starch, gelatine or gums. The thickeners take the place of letting the yogurt ferment long enough to get thicker on its own. So the consumer is left with thick yoghurt that doesn't actually have any flavour.
What makes yoghurt Greek-style?
Any yoghurt with live bacterial cultures will get thicker over time as it continues to ferment. It will also get more sour as the lactic acid level increases. That's why yoghurts from 'ethnic' shops often have a sharper taste than supermarket yoghurts. Certain groups of consumers don't like that extra sour taste, so commercial yoghurts are thickened befor the acid level gets that high. Greek-style yoghurts are thick and creamy because they are strained after fermentation without being allowed to get too tart. The liquid part (the whey) is allowed to drain out, leaving a thicker curd behind. The proteins are concentrated, making strained Greek-style yoghurt more nutritious per spoonful. Obviously no Greek-style yoghurt made at home will taste exactly like 'real' Greek yoghurt. It's a matter of different cows, fed differently plus different bacterial cultures. But the homemade yoghurt will still taste better than anything in the supermarket.
The only ingredient in Greek-style yoghurt is...yoghurt. Use plain full-fat (whole milk) organic yoghurt without sugar, flavourings and any of the thickeners mentioned above. Freshly-made yoghurt is even better. This gives the most authentic flavour and texture. The method is the same regardless of quantity. Start with one large carton of yohurt to get the technique down before moving on to mass production.
Large glass or ceramic bowl
Strainer that fits over the bowl
Tea towel (tightly woven cotton or linen), or a piece of cotton muslin the size of a tea towel
Cotton kitchen string
Coffee filter and filter paper if preferred
Clean glass jar (such as a jam jar) for the strained yoghurt
Note: As with all food preparation, work clean! That means hair tied back, impeccably clean hands and spotless counters. All utensils must be very clean. Rinse the tea towel/muslin well after washing to remove any traces of detergent. It can be boiled if desired. Don't use it for anything else. Jam jars and lids can be boiled or heated in the oven to sterilise them.
Fit the strainer over the glass bowl. There should be room for liquid to collect without touching the bottom of the strainer.
Moisten the tea towel/muslin by pouring boiling water over it. Carefully wring out the water and line the strainer with the fabric. It should hang over the strainer and bowl.
If using the coffee filter and paper, place the filter (with the paper in it) in the strainer for support.
Stir the yoghurt in the container until smooth. Spoon or pour the yoghurt into the lined strainer or the coffee filter. Gather up the edges of the tea towel/muslin to enclose the yoghurt in a bag. Tie the 'neck' formed tightly with the kitchen string, leaving some excess.
Suspend the bag of yoghurt over the bowl so the whey can drip out freely. Tying the string to the handle of an overhead kitchen cabinet works well. A coffee filter won't hold as much yoghurt and may need to be refilled periodically. Leave the yoghurt to strain in a cool place until the desired texture is achieved. This could take 2 hours or more.
Transfer the Greek-style yoghurt to a clean (sterilised) glass jar or bowl. Sweeteners and flavourings can be added at this time; mix in with a clean spoon. Cover and store in the fridge for up to a week.
Eat the Greek-style yoghurt plain or with fruit. It can be used in recipes such as Bollywood Raita