I have been making skyr a while now, always with good outcome. I started out with a Siggis brand skyr from the grocery store, but now I make it from cultures from my last make. I'm on about the 8th batch. I make it in 2 gallon batches (I can't seem to meet the demand for the stuff) with fat free p/h milk, heated to 190f(over an hour), cooled to 110f off the burner, but on the counter., usually 3+ hours. At 110f, I mix about a yogurt cup worth of culture with about a half cup of the 110 milk, till it is pourable. I mix that in, take 12-14 drops of vegetable rennet in a quarter cup of cool water, mix that in as well. then I put the whole thing, covered,into the oven with the oven light on, for 12 hours. If you leave it less or more by an hour, the curds seem to break up. Then I cut the curds, at what ever temp they came out of the oven, and pour them into 2 extra large nut milk bags. I got those on amazon, and they are awesome for draining ricotta, skyr, etc. I let them drain a couple hours, until its the consistency I want, somewhere between Greek yogurt and cream cheese, then into a big bowl and whisk it for 15 minutes or so, until smooth. If it is too dry, I add some whey back in. I do not add anything to it, leaving that for whoever gets it. I prefer it savory, like cultured sour cream, but my sister puts granola and berries in it. Very versatile, and I think the rennet helps hold everything together better. I've never had it last more than maybe 10 days, but I would guess you could get 14-21 days from it. at ten days there is no separation.