Also known as grave wax, mortuary fat, and corpse cheese, adipocere is a soap-like or waxy substance formed from the fat and soft tissue of human or animal remains after interment. Adipocere is most commonly produced in waterlogged burials and on the bodies of drowning victims, although it can also form in the presence of less moisture; thus, there are generally two types of adipocere, known respectively as 'wet' and 'dry'.

Adipocere can be anywhere between creamy off-white and brown in colour, and varies in consistency from slimy like old wet soap to solid like candle wax. When heat is applied to it, it generally behaves exactly as wax does: it first becomes pliable, and eventually clarifies and melts. In its initial stages of formation it smells of ammonia, but in later stages the odour can be anywhere between sweet and cheesy.

As noted above, the presence of moisture is necessary for the formation of adipocere. Absence of free oxygen and a cool environment are also contributory factors, and alkaline soils can help speed the process in exactly the same way that lye facilitates saponification, which is the process used to convert fat into soap. In light of this, it ought to be no surprise that corpses containing a high proportion of fat, such as those of babies and obese individuals, are more likely to be converted to adipocere.

A parting thought: formaldehyde, an ingredient in embalming fluid, is strongly alkaline; many people are now buried in sealed, air-tight caskets; adults in many western countries tend toward obesity; and corpses with a high proportion of body fat are almost certain to contain enough moisture to facilitate adipocere formation. Given all of this, it's reasonable to assume that there is a rapidly growing host of soap and wax corpses forming quietly beneath the ground in most modern cities. Just thought I'd mention it.