jamesb wrote: When making it in a jar should the lid be screwed on to make a seal so that that the kefir is fermenting inside?
This is totally optional. Airtight fermentation will result in more carbonation and a tarter taste. More carbonation means more alcohol too (maximum < 2%). I'm not sure why exactly. Maybe anaerobic yeast are able to grow faster, since they're the source of C02/alcohol? If you choose to do this, make sure you don't fill the jar more than 2/3 full. Carbon dioxide in an airtight container = increased air pressure. Otherwise put your lid on loosely or fasten a bit of kitchen towel over it with a rubber band. You could experiment with both and see which taste you prefer.