Gel appeared during serum collection - (May/16/2007 )

After collection of blood, blood was allowed to clot in room temperature for an hour. After clotting and spinning at 4000rpm for 20mins at 4C, blood cell and serum was separated. However a transparent gel was appeared, what is it? How can it be avoided?

Thank you!

My colleague encountered that before. What he did was, he mixed the blood in the Eppendorf tube by stirring it with a pipette tip. Then he centrifuged the blood again and it turned out right.

We don't know why such thing happens and whether it is alright to mix the blood and re-centrifuge.
Maybe someone else can offer some explanation on that?
Thanks