Here is my way of making yoghurt from scratch. If you buy yoghurt for this, make sure it has no preservatives, colourings, flavourings or gelatin. Greek yoghurt tends to be thick and will make up a good quark. But if you want to make your own yoghurt, this is a recipe I've cut from earlier in my blog:
I made yoghurt today. It's easy, delicious and inexpensive, costing about half the price of supermarket yoghurt. You can make yoghurt with any kind of milk, low fat cow's or from goat or sheep milk. All your equipment should be clean and make sure you use clean tea towels. Adding milk powder to the milk will make a thicker yoghurt.
You can use ordinary bought yoghurt as a starter, but make sure it doesn't contain gelatin. Generally the organic and biodynamic yoghurts have no gelatin. You can buy specialist milk thermometers, but for some reason they have very small dials. I've got a candy thermometer with a bigger dial for my older eyes. You probably need to use a thermometer until you know what the temps feel like on your clean finger. After that, it's easy enough to judge by poking your clean finger in the mix.
4 cups milk - the milk can be made with milk powder
½ cup instant milk powder, more if you want thicker yoghurt
3 tablespoons plain yoghurt at room temperature
When the temperature is reached, remove the milk from the stove. Stir in the powdered milk.
Leave the thermometer clipped to the pan and cool the milk to 40 - 50 degrees C (104 - 122F). To speed up the cooling process, you can transfer it to a cool bowl or put it in the fridge.
Add the starter. Place the plain yoghurt in a small bowl, stir in 1/3 cup of the warm milk and mix until smooth. Then stir the starter mixture into remaining milk and mix well.
Incubate the yoghurt in the crockpot (or in a warm place like an oven on low heat). Preheat the crockpot on low for about 15 minutes, until it feels very warm to the fingertips. Pour yoghurt mixture into the crockpot, cover the crockpot, and turn off the heat. At 35 to 45-minutes intervals, heat the crockpot on low for 10 to 15 minutes then turn off the heat. Be warned that if you overheat the yoghurt, it will turn into a solid blob. Don't ask me how I know that. ; )
The mix needs to incubate for 3-5 hours at a temperature of 43-45 degrees C (110 - 113F). Do not shake or disturb it during incubation. After 3 hours, check to see if the yoghurt is set by gently tilting the container. If yoghurt is set and firm, place it in the refrigerator and chill for 6 hours before serving. If not, continue to incubate. Check the yoghurt every hour and place in refrigerator as soon as it sets. The longer the yoghurt incubates the tarter the flavor will be.
If your yoghurt sets within 3 hours, but you'd prefer more tartness, continue the incubation process for another hour or so. Yoghurt making is only successful if you use fresh viable cultures, so check the use by date on your yoghurt starter and make it as soon as you can after buying it. Once you've made your own yoghurt you can use it as your next starter.
When you have your yoghurt made and you want to make quark, you need a large jug, a strainer and a piece of clean cotton cloth. Wash the cloth with pure soap, rinse well and wring it out so it's not dripping wet. Place the strainer in the jug and the cloth over the strainer. Then add the yoghurt.
The quark below is an old photo of quark I made a few months ago. The savory quark was made by adding salt and pepper to taste to the finished quark and adding some chopped chives. You could also add chilli and chilli sauce over the top of the quark.
This sweet quark below was sweetened with a little honey and then I added a small amount of homemade strawberry jam to the top of the quark.
Instead of making quark with your yoghurt, you could make frozen yoghurt popsicles or dessert. Just freeze some fruit - berries, banana, apple with a squeeze of lemon juice added to stop browning. Make sure the yoghurt is cold after making it.
If you intend making popsicles, put the frozen fruit in the blender and whizz it up. Add about ½ cup fresh orange juice and the yoghurt mix, then whizz it again until the mix is thoroughly combined. Pour the mix into popsicle molds and freeze.
Frozen yoghurt dessert
You could also make a bowl of frozen yoghurt by adding frozen fruit to a blender and whizz to break up the fruit. Add about third cup of honey and the yoghurt mix, and whizz again. Pour into a bowl and freeze.