NEVER BOIL your juice. (pasturized or no)
It can be assumed that pasturized bottled juice and frozen concentrates are devoid of microbes enough to be brought to room temp and used as is.
with unpasturized products and fresh fruits, you will do well to treat with Campden as per the standard directions prior to adding to your must.
you may - (if you intend to disolve solids into it) WARM up a bit of the juice to facilitate disolving sugars, DME, etc. but never let it boil.
I never boil juice, nor do I use pectic enzyme, and my Apfelweins are always crystal clear if allowed to settle out adaquately
In primary: Earl Gray hard cider,
In secondary: Blueberry apple Monster
Bottled: "All apple" Apfelwein, Mixed berry country wine, Kick yer' butt Hard Cider, "All apple" Achtung!Apfelwein, Kumquat mead, "All apple" hard cider.
Drinking: "All Apple" Apfelwein, Mixed Berry Country wine, Blueberry Belgian White ale.
comming to a carboy near you...
Redhook ESB clone