I really think it's hit-and-miss with the All Whites brand. Something happens during the pasteurization process that MAY prevent them from whipping up...which is why they put that warning on the carton The only time I tried that brand, they wouldn't whip up, period, and I have read other posts which relayed the same experience...as well as posts like the ones here swearing that they work! However I have NEVER had a problem with the liquid EW from Trader Joe's, nor any store/plain-wrap brand from supermarket chains. (All brands carry the warning about not whipping to meringue, though)
I did a taste test once with fresh ew, pasteurized liquid, and powdered ew, and although I do agree that the best taste came from fresh ew, the difference was only noticable when testing side-by-side with the other two methods. Liquid was nominally better than powdered, but powdered still produced a good IMBC. My only comment is that the powdered EW STINK!! when reconstituted...they smell like wet cardboard
. I seriously thought I was going to have to chuck the icing, but once everything was added the icing tasted perfectly normal.
Of course I can't answer for mamawrobin's bizarre no-whipping experience even with fresh ew....??!!