Significance of melting points of fatty acids (ie SFA vs MUFA vs PUFA)? (Should I eat my rendered duck fat?)

Answered on August 19, 2014
Created July 29, 2013 at 12:44 AM

What, if any, is the connection between the melting point of various fats and their overall fatty acid composition? For example, it is known from anecdotal experience that extra virgin olive oil or poultry fat has a lower melting point than say, tallow or ghee. Is this evidence to suggest that fatty acids more prone to oxidation (ie PUFAs) have lower melting points than more heat stable SFAs?

There are exceptions, like coconut oil's relatively low melting point among "solid" fats, but that is probably due to a higher percentage of MCTs...

Consider a scenario... I am having roast duck for dinner tomorrow. Naturally, a lot of the fat renders and drips into a pan I keep below the duck. The duck is roasted for 6 hours, starting at 200 degrees C decreasing to 175 degrees C to 150 degrees C in 2 hour increments. From past experience, I noticed that, at room temperature (ie 18 - 25 degrees C), the rendered duck fat is liquid/not completely solid long after roasting, in contrast to the crispy duck skin remaining on the bird. So, despite the fact that all the fat came originally from the same source, would it be accurate to infer that the rendered fat would contain largely PUFAs (and some MUFA) rather than SFAs that would be more concentrated on the intact skin?

This can be essentially applied to any cooked animal... is the "greasiness" of the meat indicative of a higher PUFA concentration than its solid counterpart? Or am I missing the point completely by ignoring residues of amino acids, vitamins, etc. in the fat itself?

Should I save that rendered duck fat, or forego it in order to minimize PUFA consumption?

Vaguely similar question:




on August 06, 2013
at 01:25 AM

Thanks all. This is what I used the duck fat for: http://everydaypaleo.com/duck-fat-roasted-garlic-sweet-potatoes-oh-yeah/. :)

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on July 29, 2013
at 01:26 AM

Eat the fat. You're WAY overthinking this.

The melting point of fats is normally manipulated in a hydrogenater. This adds hydrogen at the unsaturation sites in a PUFA, saturating it and making a synthetic saturated fat with a higher melt point. Crisco is a good example of this synthetic lard.

This isn't what you're doing in the oven. You're running a rendering plant, melting the fat and recovering it. You may not do it quite as well as a commercial plant, but you end up with virtually the same thing, with properties very close to what is published in the food tables. You might oxidize it a little more than Rougie does, but you're also starting with a very high quality bird instead of industrial food processing scraps.

Would Grok throw out home-made duck fat? I don't think so. You've done better with your stove than anyone could ever do over an open fire.



on July 29, 2013
at 01:06 AM

I am fairly sure it all melts and drips at those temperatures and over that time. What you find in the pan is the original composition. I would eat it of course, and even better roast potatoes or other roots in it.



on July 29, 2013
at 02:07 AM

At roasting temperature, all fats are liquid. Rendering fat is more than simply melting it, it's liberating it from the cellular structure. What fat is left after cooking the duck isn't just saturated fat, it's just fat that hasn't been cooked out of the fat tissue.

In general, melting points trend as Saturated > MUFA > PUFA. It's all about how well the molecules pack together. Unsaturated fats have large bends in their structure, so it's harder to stack together in a solid form. The more kinks in the fat, the harder it is to form a solid. Trans-fats are the exception to the unsaturated fat rule because they don't have a bend in them, they more resemble saturated fats in shape.

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