There's no better approach for barbel (and big chub and roach) in low temperatures and low clear rivers than maggots,casters and hemp. I tend not to use hemp much in high, coloured water - I prefer to use larger, more smelly baits. In clear water though, a good bed of hemp will give barbel something to 'root' about for. Also, maggots/casters and hemp are far less filling than pellets and boilies. Remember, in colder temperatures, fish don't need to eat so much and consequently will only feed for short periods - that's why a particle approach is generally the best way to snare the odd barbel when other methods fail miserably. So the answer to your question Chris is yes, hemp is a good winter bait. One final point - I don't like to use frozen hemp, I like mine freshly cooked and with a fair dollop of salt in it.