Experimenting with Bag-in-Box

[alan.monaghan]

I'm trying a new technique (to me anyway!) of finishing my brew in a bag-in-box rather than a barrel. The aim is to serve it via a beer engine without letting air into the beer (ie allowing the bag to collapse as the beer is drawn off). All is going well but I'm puzzled by whats happening during secondary fermentation and wondered whether anyone has had similar experiences.
My brew is 16 litres (3kg LME, 170 gm Crystal Malt, 20gm Magnum boiling hops, 10gm Magnum finishing hops, half tsp Irish Moss) and primary fermentation appeared normal, stopping after 8-9 days. I used 1.5 oz of priming sugar and racked it into a 10 litre BIB, a 5litr BIB and a 1Litre bottle (for monitoring). After 10 days conditioning in the bottle the beer has cleared perfectly and everything appers normal, but the beer in the BIBs is still fermenting away merrily. I've got them with the taps at the top for the moment so I can easily vent off CO2 every day to avoid the bags bursting. The resulting smell is fantastic and the beer seems to be clearing well so far as I can tell. I just feel that fermentation should have stopprd by now, but as I haven't had any previous experince of brewing this way I can't be sure. Does anyone know if this is normal