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All that FAT! Removing grease and why you should heat.

Discussion in 'Skulls and Skeletons' started by Sea Wolf, Jul 4, 2012.

  1. Sea Wolf

    Sea Wolf Well-Known Member

    Fat and grease are fine in the right places. Not in skulls we want to make pretty though. To help folks understand why you don't need super high temperatures to get fat out of bone (and that cold temperatures are a poor choice) I put together some information on melting temperatures of fats. If you base assumptions of degreasing on lard (animal fat), soft lard melts at between 86 to 104 F. The harder, solid, "leaf lard" melts at 109 to 118 F and the fat in general melts at between 97 to 113 F.

    PIG fat melting points:
    backfat: 86–104 °F
    leaf fat: 109–118 °F (solid kidney fat deposits)
    mixed fat: 97–113 °F)

    Lard is the rendered belly fat from pigs [Sus domestica] and is soluble in benzene, chloroform, ether, slightly in alcohol and insoluble in water and melts at 97 to 107° (F).

    Tallow is the internal fat (suet) surrounding the kidneys and intestines of sheep, goats, deer and oxen that is rendered down at a very low heat, just enough to cause the grease to melt away from the connective tissues. Tallow is also harder than lard and has a higher melting point. 109 - 114°F for beef tallow as opposed to pork lard in general.

    Bear fat, commonly called bear grease is the material rendered from the body fat of any species of bears [Ursus spp.], and was commonly used as a lubricant, lamp oil and to make the finest croissant, according to the French. Bear fat melts at or a little above 80°.

    Bird fats generally have a melting point of 98°F.

    I don't know of anyone that has a tank of benzene to soak skulls in so we make do with other, safer solvents for the fats in bone. Notably, detergents. Detergents do not dissolve the fat but break it down into smaller particles and float it away in a water solution. To do this as fast as possible, the fat has to be at its melting point to allow the detergent to break it down and move it out of the bone. Fat that is not at it's melting point will remain solid and unresponsive to the action of detergents. Take two cups. Put detergent solution in both. Heat one and leave the other at even room temperature. Add a half teaspoon of lard to each one and let it sit for a few hours. Stir and you will find that the heated cup now will have the fat in solution. The unheated one will still be a chunk of lard staring at you.

    There is no need to be heating your degreasing solutions to over 120°F. Heating the bone above that point over a long term as in degreasing will begin to break down the supportive structure of the bone itself and it may eventually fail and degrade. Simply keeping the degreasing solution heated to at least 115°F and not higher than 120°F should be enough to cover the range of fat melting points in any species that you work with without damaging the bone structure itself. Cervids and Caprinae will still require a temperature of 120 degrees to break down the fat type they have. Other techniques such as circulating the degreasing solution can also help to speed the process.
    Last edited: Dec 4, 2019
    Bevill and landdepot like this.
  2. Re: All that FAT!

    Excellent and very useful post. One thing I would add is that acetone, which many of use as part of the degreasing process on some skulls, is a good solvent for fat, though not as good as benzene, chloroform, or ether. But acetone is safer and easier to come by.

  3. Re: All that FAT!

    Very informative post
  4. Re: All that FAT!

    Good Info Seawolf, thanks.
  5. Sea Wolf

    Sea Wolf Well-Known Member

    Re: All that FAT!

    It's the 4th. Home alone and I'm bored. .. Yes, forgot to mention acetone. But I would use that on thin, frail specimens or later in the detergent degreasing for the ones you want to shake a stick at. Acetone makes a very good stick. You don't want to heat it as it is dangerous enough as it is but you don't want the container to be chilled either. Room temperature for something that has residual grease in it will work fine with acetone. Using it on antlered skulls is problematic due to the antlers themselves creating an issue in getting them into a container that can hold acetone and be sealed.
    Last edited: Dec 4, 2019
  6. White Stag

    White Stag New Member

    Re: All that FAT!

    Very interesting post!
  7. horsefeathers

    horsefeathers Member

    Re: All that FAT!

    Very useful! Too bad we can't get specific fat melting points on a species by species basis...
  8. Re: All that FAT!

    Be nice to know where a deer skull falls in here.
  9. Re: All that FAT!

    Thanks Sea Wolf!!!!!!!
  10. cyclone

    cyclone Posts: 400001

    Re: All that FAT!

  11. Sea Wolf

    Sea Wolf Well-Known Member

    Re: All that FAT!

    Thanks Cyclone. I did look for species information. About all I found was that equine fat melts at 78°F, canine at around 90°F and deer fat was a lot closer to tallow in consistency and behavior at 118°F. One reason why when eating deer fat in food as well as lamb, as the cooked food cools, the fat starts coating your teeth and inside of your mouth. Deer and sheep seemed to be the only species I found that crossed the line of 115°F.
    Last edited: Dec 4, 2019
  12. Re: All that FAT!

    Friend and I just picked up some pigs, I guess I'll be sending them some place for proper degreasing. Seriously, Seawolf, thank you for this info! :)
  13. Re: All that FAT!

    kinda wondering what my belly fat melting point is???? ;)
    Dave York likes this.
  14. Sea Wolf

    Sea Wolf Well-Known Member

    Re: All that FAT!

    I have to get to the college to access a paper that will have more species information as to melting points. Including human. :)
  15. Re: All that FAT!

    Thanks Sea Wolf. Now what dissolves adipocere? I'm just doing a trial now with methanol and seems to be going okay. Thoughts?
  16. AH7

    AH7 New Member

    Re: All that FAT!

    That is a great questions! If you figure out what dissolves adipocere, that will be hugely valuable.

    Also, Sea Wolf, why not write more about the melting point of collagen. A few weeks ago, I wrote a bit about this (i.e., why not heat your skulls so high), but a more detailed run down would be very useful. I know this kind of thing takes time, but if you wrote details about that, then we would have a real techincal bracket for the optimal temperature range!

    Regardless, the info about the fat points is hugely valuable. Thanks for that.
  17. Sea Wolf

    Sea Wolf Well-Known Member

    Re: All that FAT!

    Thanks. I was going to try and do a tasteful addition on adipocere. I'll do Fat .. you do Collagen and I'll add it to the main post. :) Yeah .. it does take time and I still need to access the JSTOR database. :)
  18. Re: All that FAT!

    Thanks, Sea woof. You're so helpful.
  19. AH7

    AH7 New Member

    Re: All that FAT!

    Hi Sea Wolf (and all others),

    I have access to ALL publications. Just send me citations you need and I'll get you the PDFs. Most can be found immediately, but older ones I'll order for you.
  20. Re: All that FAT!

    Great post, very informative SW.

    I'll keep my eye out for your future additional info.