For the source text click/tap here: Chullin 120
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The Gemara on our daf teaches that the prohibition on both blood and forbidden fats remains in force even if the form is changed. Thus, even if blood was processed so that it became solid, or even if the forbidden fat was melted so that it became liquid, nevertheless the same rules apply.
Regarding solidified blood, the Gemara recognizes that the prohibition should remain in force, since now the blood would be considered a food, and the prohibition to eat blood (see, for example, Vayikra 3:17) applies. Forbidden fats in liquid form, however, appear to the Gemara to present a problem, for the Torah specifically forbids eating these fats, and there is no clear source prohibiting them from being drunk. Ultimately, Reish Lakish suggests a source that would include drinking in the prohibition, as well.
We explore the history of tallow.