the cream will start to feel thicker as you shake it, making it MUCH harder to shake around, the easiest shaking method is to take the jar by the "neck" or the closest part to the lid, and shake downwards in a stabbing motion back and forth. Eventually the jar seems easier, and easier to shake, open the jar and peek inside, see butter? This is when the butter starts to seperate from the buttermilk, once you see the little clumps of butter inside the jar, begin to strain out the extra liquid (i recommend you save this, it is the buttermilk, and when home-made it tastes sweet, and is often used in baking i.e. pancakes,biscuits,etc; After straining the buttermilk you have the remeaining butter in the jar, just scoop it into a storage container and pat it down a bit, youll want to put it in the fridge to harden it a bit more so its easier to scoop and spread.
[the picture below is before straining out all of the buttermilk]
I have only one correction. The liquid left after making butter is NOT buttermilk it is skim milk. Buttermilk is cultured. For info on buttermilk or general milk/butter/cheese/yogurt-yes you can make your own yogurt go to this site: http://biology.clc.uc.edu/fankhauser/Cheese/Cheese_course/Cheese_course.htm
great pictures.
Hormones / Preservatives shouldn't be in processed cream anyway. If the hormone is used at the farm, then it will be present in both raw and pastuerised milk. Good butter will only ever contain Salt as a preservative anyway, so making your own is no better than buying shop bought.
http://en.wikipedia.org/wiki/Buttermilk
http://biology.clc.uc.edu/Fankhauser/Cheese/BUTTERMILK.HTM#old_fashioned_buttermilk
More information on making butter:
http://en.wikipedia.org/wiki/Churning_%28butter%29
http://en.wikipedia.org/wiki/Butter
http://www.motherearthnews.com/Real-Food/1978-03-01/How-to-Make-Fresh-Butter-without-a-separator-without-a-churn-and-without.aspx
http://webexhibits.org/butter/making.html
I've glanced quickly at a dozen other pages from a google search; they all refer to the liquid remnant as "buttermilk", whether the process involved souring the milk/cream first, or not.
Butter will spoil faster when there is buttermilk in it, so it is important to remove as much as possible.
After you have poured off the buttermilk, put the butter in a bowl and work it with a spoon, have the bowl on an angle and drain off as much as you can. Now add some ice cold water and work it into the butter and this will draw out the remaining buttermilk. Drain off water and you are done.
I also start out by letting the heavy cream sit out in room temp. for 12 hours.
Doing this will start a chemical reaction that will help break down the casings that the fat cells are in. This will reduce the time it takes to release the butter. I only need to shake the jar for about 3 min, not 20.
Have fun.
The times I've done this, I haven't had too strain it, if you just keep shaking and knocking the butter to the sides, It will form itself into almost a stick of butter by it'self. I usually pour out the milk and I can usually shake out the bar of butter.