About this blog...

Food has been an important part of my life for as long as I can remember. Food and the festivities surrounding its arrival to the table has always been a focal point in our family. For many years I have been amassing the cookbooks, recipe cards, cooking journals, diaries, manuscripts and clipping files of our once extensive family.

Personally, I’ve been professionally involved with food for over 40 years in numerous and varied culinary capacities across the country so I also have the collected stories, as well as current and on-going food-related experiences from my own life I’d like to share.

My idea has long been that someday I would bring all of this marvelous raw material together into a culinary journey through our family’s heritage. This journal is the beginnings of that journey.

Sunday, January 23, 2011

Cream from Milk - Mechanical Separation

Today I need to separate the cream out of about 10 gallons of goats milk in anticipation of churning some goat butter tomorrow.
Goats milk is quite different in composition and construction than cow’s milk.  Take the cream, for example.  With unprocessed (specifically, not homogenized) cow’s milk, the cream will readily rise to the surface if left alone for a few hours or overnight.  Not so with goats milk.
Goats milk is said to be "naturally homogenized" because the butter fat molecules in goats milk are so much smaller  by comparison to those in cow’s milk, that they more easily stay suspended in the liquid. (This coincidentally , is one of the reasons that goats milk is considered to be much easier to digest than cow’s milk).
In order to get the cream out of goats milk - either to obtain the cream for other use or to make a lower fat milk product - it must be mechanically separated.  Typically, the way this is done is with an apparatus called a "cream separator" (imagine that!).
Cream separators come in many sizes/capacities and can be successfully made from a number of different materials but nearly all work on the same operating principle: centrifugal force*.  Even though the butter fat molecules are small and in suspension they are still lighter than water (the primary component of milk) and so the act of accelerated spinning works to separate the fat from the milk. From that point all that is left to do is send the butterfat-rich milk (cream) in one direction and the butterfat-poor milk (skim milk) another.
Cream separators have lots of parts that have to go together in just the correct order for it to work properly.  Mine, an old Russian-made, hand crank model with predominantly plastic parts, has over 20 milk-contact parts, plus the crank/transmission unit. 
Here are several pictures of the parts, the sub-assemblies, and final assembly...

To get the best results from a cream separator the most important thing (aside from the correct assembly of all the parts) is to have the milk at the proper temperature.  I have found that 101-103 degrees F (which happens to be a normal goat's body temperature) works best for goats milk.  Too hot and it seems not to get all the cream out of the milk.  Too cool and it gums up the separator plates, clogging up the works.  My unit has a set-screw adjustment that is supposed to let you make heavy, medium, or light cream but it does not seem to have any effect when I have tried it.
The actual separating is easy.  Once the milk is to temperature it is poured into the hopper.  The crank is turned at about 60 rpm (one revolution per second). The flag valve is opened and a stream of milk flows to the bottom of the assembly of plates which, because of the gearing, are now spinning quite fast.  The milk flows through the plates which have a series of holes that direct the heavier elements one way and the lighter another.  The two streams of separated milk find their way to the 2 spouts with a pretty good flow of skim milk going one way and a smaller drizzle of cream the other.

My hopper takes about a gallon of milk so it had to be refilled several times. DO NOT stop turning the crank when there is milk flowing through the machine or it will make a huge mess by flowing out everywhere except from where it is supposed to!
I normally expect to get about a quart of cream from 4 gallons of milk but I had never separated cream at this time of year.  We know from both the milk quality testing we do and the cheese yields we get, that our milk gets much richer in the fall and winter than it is in the summer. We have individual goats who we know can produce milk with about 10% butterfat late in the year (by comparison, regular whole milk at the store is about 3.5% butterfat), but I was still surprised by my yield. 
Today I got 6 quarts of very heavy cream from the 10 gallons of milk!
Tomorrow I will be churning all that cream into Goats Milk Butter.
*Strictly speaking there is no such thing as "centrifugal force". The force we commonly refer to as centrifugal is actually the inverse or absence of "centripetal force".  Confused? Look it up.  Here's a place to start... http://en.wikipedia.org/wiki/Centrifugal_force

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