Heat milk in a large pot over medium-low heat, stirring frequently, until it registers between 178°F to 190°F (80°C to 90°C) on the thermometer. (see notes)
Turn off the heat and add the yogurt. Stir for 10-15 seconds and let sit for 2 minutes.
Add half the vinegar and mix again for 10 seconds. Then let it sit for another 2 minutes.
Stir in the other half of the vinegar and mix for one minute.
Set aside until it reaches room temperature (about 1 hour), so the curd will form.
Line a large colander with 2 layers of cheesecloth or a clean kitchen towel and place it over a large bowl.
Transfer curds to the colander, cover, and allow to drain for about 20 minutes.
When most of the whey has drained off, lift the edges of the cheesecloth up and twist, wrapping the cheese into a ball; then carefully squeeze off excess whey.
Place the cheese on a container and add salt to taste. Mix well with a wooden spoon (read notes).
Now shape the cheese using molds (I used cookie molds) or use one or two bowls.
Place Queso Fresco in the refrigerator and let it sit for a couple of hours or overnight before eating.
Notes
This recipe yields 740 gr (about 1 ½ lb) of fresh cheese.
If you do not have a thermometer, you will notice that the milk begins to make little bubbles around the edges of the pot, that would be the exact moment when you need to add yogurt and vinegar.
I’ve noticed that when I don’t let the curds cool completely, the cheese tends to get creamy, so it’s important to let it cool completely if you want a cheese that crumbles well.
If it's the first time you make the Queso Fresco recipe, you might notice that the cheese is a bit creamy (like cream cheese); this may be for several reasons. For example overmixing when seasoning with salt or pressing so hard when shaping.
You can omit the yogurt if you want, just add one more tablespoon of vinegar.
Making Queso Fresco with the exactly crumbly texture from the store-bought version takes a bit of practice. The first few times it will tend to be creamy, other times it will be a little crumbly (like cottage cheese). The important thing is the taste. So don’t get discouraged and keep trying until you’ll reach the texture you prefer.