I've been making homemade yogurt for several years due to a family member with crohn's. It is extremely easy and much more healthy than store bought.
The liquid on top is whey, but there is little sugar as it has been converted by the culture.
I ferment it for 24 hours which allows the live culture to consume the lactose and increase the level of good bacteria culture.
Store bought yogurts only culture for a few hours due to production time and add milk solids, starches and whatnot to thicken it up. Not all of the lactose is converted in this time frame.
Like any other processed product, yogurt, live cultured or not varies drastically when made in a plant vs in your kitchen.
People with milk intolerance handle yogurt made in this way very well and can replenish healthy gut flora.
Most store bought yogurt is not live culture and the ones that are, may be high in sugar and other additives such as milk solids and whatnot.
Sometimes I make cream cheese by simply straining the yogurt.
Healthy cream cheese, low lactose content, high in protein, high in beneficial flora content.
This cream cheese can be used in place of sour cream, used as a meat tenderiser or sandwitch spread.
I call it cream cheese which it is, others call it greek yogurt (it's not greek, and is popular in most societies that ferment food).
I use the yogurt every a.m. in fruit and protein smoothies.
Cost me $3 for 2 liters (Roughly 2 quarts for the metric shy).
Cheap, easier than anything else you make, far better and cheaper than anything you can buy, vast health benefits ......
If you consume dairy, this should be at the top of your list!
If you can make kraft dinner you can make yogurt and cream cheese (greek yogurt).