determining the fat content of cream

[pastrygirl]

There is a local farmer who provides us with fresh cream on occasion. This is great, except for the fact that it seems really inconsistent. Sometimes it seems like almost butter, other times closer to the 40% manufacturing cream that I used to get in the US. The good thing about this cream is that it will actually whip, unlike the 25% UHT packaged cream that is the alternative. The problem is, the inconsistency really messes with my ice cream production, to the point that I am tempted to use the more consistent packaged product over the fresh local one. Heresy, I know.

Lacking a centrifuge, is there any way to determine the fat content of cream on a batch to batch basis? Any ideas on how to allow for this inconsistency in my ice cream without resorting to the UHT stuff?

[dougal]

I'm not sure whether there is any quick, kitchen-practical, low-tech method for you.

It seems that commercially its done by adding (really strong) sulphuric acid and then centrifuging the milk to gather the solids together.

http://en.wikipedia.org/wiki/Babcock_test

http://en.wikipedia.org/wiki/Gerber_method

I don't think that density measurement (with for example a simple winemaker's hydrometer) will tell you anything useful.

I just wonder whether viscosity measurement (at a standardised temperature) might be worthwhile. This would be something like measuring the time for a ball bearing to fall down a long narrow (glass?) tube full of the cream... The longer the time to drop the standard distance, the more viscous, indicating a higher fat content. (The ball bearing would need to be something like 90% or more of the width of the tube - making it hard for the cream to flow round it as it falls, and so you can see, rather than just hear, where it is!)

I wonder if your requirement for consistency of product qualities (rather than just consistency of product quantity) could be be put to your supplier?

I'd suspect that inconsistent processing (skimming) might have a lot to do with it. Maybe the difference you are seeing is the difference between the first and the last stuff to come off the skimmer?

Explaining the reason for your need for consistency might be easier than measuring whatever it might be that you've been sent today!

One of the things I recall from an old book on cheesemaking is that there was a difference between milk from morning and evening milkings. And of course with the grazing fodder and seasonal variations.

But in terms of day-to-day product variation, I suspect that it might be helpful to explain carefully that while the average quality is fine, its the variability that gives you a problem.

And it sounds as though your "supply chain" might be short enough for you to speak directly with the skimmer operator! If you have the opportunity of 'local sourcing' then you should be able to (diplomatically) create the opportunity to get a little input into the production process!

I'd certainly try and see what could be achieved in that direction before changing to a non-local and heavily processed product.

Some variability is one of the glories of a truly natural product!

[pastrygirl]

Some variability is one of the glories of a truly natural product!

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True, I suppose we may just have to get to know the cream, and learn how to adust when necessary. It would be wrong not to use it.

[Stephanie Wallace]

Measure out 500 grams of cream then boil until all of the water content has evaporated. Skim or strain the leftover solids, then weigh the remaining fat.

[jgm]

If you use some of the above methods to figure it out, I would think you could establish some sort of "standard" - i.e. 8 fluid ounces of X% cream weighs ___ oz.

[paulraphael]

I don't think that density measurement (with for example a simple winemaker's hydrometer) will tell you anything useful.

I wonder why it wouldn't. Cream has a pretty low proportion of milk solids, right? So by far the most important components are water and fat, which have very different densities.

Why wouldn't a density measurement at least get you within a couple of percent (once you figure out the formula)?

[tim]

Hi,

I would think you could carefully measure one pint of skim milk, I assume it would weight exactly 16 ounces. Then weigh one pint of 40% heavy cream or 25% cream and calculate the weight per ounce.

The difference would be the fat content and would provide you with the algebraic formula for adjusting the farm fresh cream with skim milk to achieve that 40% product.

Tim

[paulraphael]

Here's an idea for anyone who likes experimenting more than they like math:

Get a cheap hygrometer (or improvise one). Drop it into milks and creams of known fat content. Put your own marks on the side with something indellible. If you have marks for 0, 2, 4, 20, 30, 36, 40 percent (or whatever you come up with) you'll be able to estimate reasonably well for cream percentages that fall between the lines.