Lower extremity of newborn, under running water for several months - formation of “adipocere”
One of the most interesting things to find in a cadaver is when adipocere forms. This so-called “grave wax” shows that a body is at least several months old, as it takes a while for the biochemical reactions to take place that form this substance.
While most cadavers go through the full decomposition process and are rotted away by bacteria and other organisms, bodies that form adipocere begin a process of anaerobic bacterial hydrolysis at the start of the putrefaction stage of decomposition. As most of the proteins in the body are digested, the fat in the body racidifies, and instead of being digested with everything else, breaks down into glycerine, fatty solids (saturated fats), and fluid fatty acids (unsaturated fat). The glycerine and fluid fatty acids are washed away or dissolved, and the solid fat remains behind, forming a cast of the body.
Adipocere is white or gray, and very much like thick cottage cheese in its crumbly texture. It’s very hardy and preservative in quality, and cadavers over 700 years old have been found to have easily-discernible fine facial structures because of it. However, the formation of the substance requires very specific conditions to be met, the most important of which is a body with a relatively high fat content (though there are occasional exceptions). Because of this, infants, young women, and the obese are most likely to be found in this state.
Atlas of Legal Medicine. Dr. Eduard von Hofmann, 1898.