Wust, C.J. (1992). Microbiology 439: “Immunology Laboratory Manual”. p. 8-9.
“Serum is obtained from whole blood by “ringing the clot” in the beaker with a wooden applicator stick about 20 minutes after initial collection encouraging clot retraction and thus increased serum yield. This clot is then suspended on an applicator stick platform over a funnel and collection container. This clot suspension is stored at room temperature for several hours before overnight storage at 4 degrees C. After cold storage the serum is further isolated by centrifugation (for Sure Sep TM technique accompanying page) at and collecting of the supernatant fluid. Higher speed (10000 x g) refrigerated centrifugation is usually applied subsequently to obtain the cleanest sera.”