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To the casual onlooker, fat seems like a mass of yellow-white material, composed of lipids. Biologically speaking however, rather than being a large mass, it's actually divided among countless cells, each of which is composed chiefly of lipids stored in vacuoles, in addition to a few other organelles. In essence, while it looks like a giant mass, akin to a big pile of coconut oil, it's practically more like a big pile of sandwich baggies, each filled with coconut oil, and a small amount of rice for good measure.

Yet when rendered, fat melts as if the cells and structure didn't exist, and many food animals are bred to have fat that melts at slightly above body temperature. These two models, the pile of coconut oil, and the pile of baggies of coconut oil, seem to conflict when it comes to expected behavior. For the latter to act like the former, the cells would have to be broken down, but I wouldn't expect cell membranes to rupture at just above body temperature.

So my mental model is badly predicting reality. Where is it wrong?

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    $\begingroup$ "many food animals are bred to have fat that melts at slightly above body temperature" - can you cite this? $\endgroup$
    – Bryan Krause
    Jul 23, 2021 at 19:51
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    $\begingroup$ Melting point of the fat is not the same as rendering temperature. $\endgroup$
    – Armand
    Jul 24, 2021 at 15:41
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    $\begingroup$ Interesting question connecting biology and industrial processes! Re: " it's practically more like a big pile of sandwich baggies, each filled with coconut oil," I think a better analogy would be soap bubbles rather than baggies. The phospholipid membranes (which also contain a lot of lipids) are not physically robust. The general descriptions of the rendering process indicate a main goal is to remove the water; the remaining material is fats and a proteinaceous meal. Without water, the membranes should all go away as you won't be able to maintain the bilayer anymore. $\endgroup$
    – Armand
    Jul 25, 2021 at 0:27
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    $\begingroup$ @TheEnvironmentalist I would say Armand's comment just before yours should explain the confusion. $\endgroup$
    – Bryan Krause
    Jul 26, 2021 at 16:45

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