How to determine fat percentage?

[alblancher]

I am constantly faced with the problem of determining how much fat to add to the meat I am going to grind for sausage.  As many of you know most recipes call for the raw sausage to contain a certain percentage of fat  usually around 20%.  As a rule I have usually cut just the visible fat from the meat and weigh it separately from the muscle meat to determine the percentage of fat.  I was a bit bored this morning and started playing around with the question "how do you determine the amount of fat in a cut of meat".  I decided to look at the density of the cut of meat.

Goggle says the density of fat is about 900g/liter of volume  that's the reason it floats

the density of muscle tissue is 1060 g/liter of volume  the reason pure muscle meat does not float.

The density of water is 1000g/liter

Playing around with a bit of simple math I have calculated that a piece of meat with 85% muscle and 15% fat, placed in a bucket of water will suspend.  Meaning that it will neither sink nor float.  To determine the percentage of fat in cuts that float (have more than 15% fat) you will need to submerge the cut of meat (with a very small cross sectional probe like a bamboo skewer) and measure the volume of water displaced to determine the volume of the cut of meat.   Using this volume you can calculate the total percentage of fat in the cut of meat.

Please humor me and either debunk this method and supply a fairly accurate way to determine the amount of fat in a cut of meat or expand on my train of thought.

Thanks,

Al

 

[alblancher]

As a side note

If you know that 15/85 meat suspends you can cut out enough visable fat to make the meat suspend, then add back by weight the amount of fat to get to your desired fat/muscle ration

 

[chainsaw]

You have done a lot of work & a good job figuring all this out. I never thought about measuring the ratio.

We always grind up everything together from a butt when we make sausage, otherwise it seems too dry.

 

[DanMcG]

Al, nice work! I guess you were a little more bored and a little smarter when it comes to you new method of calculating fat content. I always do what you use to do , separate it into muscle and fat then combine it to the ratio you want. Surprisingly enough I was able to follow your logic on the weight and it makes sense!

Can't you just measure the weight of a liter of meat to determine it's ratio?

I wonder what a liter of 70/30 would weigh

 

[alblancher]

Thanks guys,

I don't think you will be able to account for all the dead air space by weighing a liter of meat.  By using displacement the water seeps into all the cracks and crevices.   If you determine what the density of the piece of meat is you can determine the ratio of fat to muscle  assuming of course that all bone is removed from the meat.  If others do the calculations and determine that 15/85 meat would indeed "suspend" in a water bath then it would be just a matter of developing a chart to determine how much additional "fat" to either add or remove per Kg of dry weight to get your desired ratio.

I would like to know how they do this in a manufacturing facility.

 

[shooterrick]

Well I think I read something in Ryteks book about this.  Not sure so will look if and when I get that bored and get back with ya.  LOL.   Good JOb on this but for me anyways I just do a ruff estimate by your original method of weights. 

 

[pops6927]

Here's what industry uses:

http://dsctest.com/dsc_fat-testers.php?gclid=CM_d7OCC-aMCFYLt7Qodd0FlIw

 

[alblancher]

Interesting link.  I wonder how they would fit a pork butt into something like that?

AL

 

[boatnut]

I'm not scientific enough for all that.   Based on personal experience, I use the whole butt (non trimmed) for breakfast sausage and turns out good.  I'm "guestimating" that it's about 80/20 or so.  For a lot of my cased sausages, I will add back fat and/or bacon as I feel that a 70/30 mix for those types of sausage works better.   Nothing "wurst" then a "dry" sausage.