Issue with cookie age saveSizeToCookie

I tried following
treegrid.saveSizeToCookie(“expires=Fri, 31-Dec-2011 23:59:59 GMT”);

it created a cookie with
name = gridSettingsexpires
content = Fri, 31-Dec-2011 23:59:59 GMT=632,80,60,70,70,70,80,80,80,80,40,40,40,40,40|250,80,60,70,70,70,80,80,80,80,40,40,40,40,40|||

expiry = At end of session

Not exactly what I expected. How can I fix it?
Also is it possible to set max-age instead of expiry?

change command as

treegrid.saveSizeToCookie("; expires=Fri, 31-Dec-2011 23:59:59 GMT");