David Carment writes:

 If peanut butter has the same chemical stabilizers as a McDonald's
 milkshake, then you are ok. Go ahead and  eat it. I left said shake in
 Friend's Toyota> It stayed a  summer and winter hidden in the trunk.
 When found, same consitency, firmness, odour and flavour as
 before.......mmmmmm

 I have to point out a subtle mistake in the above account. You have referred
 to the MacDonalds product as a *milkshake*. You will find that MacDonalds
 <and their competitors too> NEVER call them MILKshakes. They are always 
 described as "SHAKES". I don't think they are allowed to call them milkshakes
 on account of the absence of said dairy substance from the "product". 

 As to what they are actually made out of, who knows? As David pointed out,
 they don't melt when warmed......could they be used as viscosity improvers
 in motor oil perhaps? Who cares how hot the oil gets! I've got a strawberry
 shake in the sump!

 Dave