Berkefeld filter:
A Berkefeld filter[1] is a water filter made of diatomaceous earth (Kieselguhr). It was invented in Germany in 1891, and by 1922 was being marketed in the United Kingdom by the Berkefeld Filter Co.[2] Berkefeld was the name of owner of the mine in Hanover, Germany, where the ceramic material was obtained.
The Berkefeld is a good bacterial water filter used in microbiological laboratories, in homes and out in the field. [Wikipedia]
Seen while trying to track down how to make insulin, mostly in survivalist forums (I’m not a survivalist). Much of it seems to be copied from a single source. As an example:
After passing through the filter the Insulin is retested carefully to determine its potency. There is practically no loss in berkefelding. The tested Insulin is poured into sterile glass vials with aseptic precautions and the sterility of the final product thoroughly tested by approved methods.
I believe this is an outtake from the original publication from the 1920s.