I usually spend part of my Sundays at our local makerspace playing with solar stuff. Last week we made solar churned butter and some ghee.
We also made butter by hand, which while involving more work is faster than the simple yet slow solar churn.
For butter you will need some heavy whipping cream, and a few canning jars of different sizes.
A widemouth pint jar works well, as it is not too cumbersome to shake. And that's how you do it, fill up the jar halfway with cream, screw the lid on tightly, and then shake the s*#& out of it for about 15 minutes.
Shown (L to R) is quart heavy cream, pint shaker jar, half pint of whey, and half pint of Ghee.
Step 1: The Stages of Butter
It is interesting to note the changes that happen. First, you get a light whipped cream mix. Then, you end up with a stiff whipped cream. (if you are going for whipped cream instead of butter, you can add sugar to the mix before you start shaking it). After awhile you get a stage where the butter is starting to form in little granules, but has not merged into a single mass. And, finally the butter all comes together and releases its whey. Pour off the whey into another jar, and start shaking the butter again. It will continue to release more whey until it finally stops.
It appears that about half of the volume becomes butter, and the other half is the whey (which I am told becomes buttermilk if you add a little bit of vinegar to it).
At this point you can add a bit of salt and stir it into your butter, as some folks don't really like the taste of unsalted butter. (bland).
This is a great workout, and quite an exercise. It helps to have another person, so that when your arms get tired you can hand it off and recuperate.
Photo shows butter granules and whey.
Step 2: Simple Solar Churn
The solar churn is a simple 25W solar panel hooked up to a 12/24V small motor and transmission (I used an old slot machine motor and assembly), and a pint jar held in place with wire. It is not the fastest system in the world, and takes about an hour to make the butter. But we don't care, because it's free solar energy, is off grid, and we don't even have to watch it except to check occasionally. The gearbox spins at about 40-50 rpm, and a higher rpm unit would probably make the butter much much faster. But we work with what we got.
In the second photo you can see the butter forming inside the jar.
Step 3: Gee, It's Ghee.
To make the solar Ghee, we take a portion, or all of the butter we've made, and put the jar into a standard box solar oven for about 15 to 20 minutes or so. What happens is that the butter melts and separates into the oil (ghee) and the milk solids that are in the butter. The milk solids tend to settle to the bottom of the jar, and the oil is easily decanted by carefully pouring it off the top into another jar. One reason folks like Ghee is that you do not need to refrigerate it it is rumored. And you could probably take the leftover milk solids and pour it over some fresh popcorn for a tasty yet very fattening snack.
You can also use a small square foot solar cooker with 3 mirrors (see my other posts) and set your jar in the middle of that to melt the butter for ghee. Total cost of the mirrors is about $6 unless you have a glass cutter and an old mirror in the garage. You can cover the butter jar with another larger jar to melt the butter much faster, however it will melt without the outer jar. Just takes longer. It also helps to paint the outside of your butter jar flat black to help it gather heat more quickly.
You probably could set the jar is some hot water, or carefully on your stove to gently (or in a low oven) heat it up, and then decant it.
But using the sun is free, and we think Little Miss Muffet would approve.