lgb81. You have raised a very interesting question and it's one that could have ramifications for all.

First you need to identify whether it is the fish pieces in burley that attract the quarry, or is it the scent? If we look at most predators, then it's my belief the scent is of far more importance, oil spreads far and wide and won't be eaten or dispersed by the small bait fish.

I would respectfully suggest you try a little experiment, instead of carrying heavy, frozen burley bottles, on one of your trips carry a bucket with a large packet or two of porridge cereal (or similar) stale bread minced into breadcrumbs is ideal, plus a bottle of some highly potent fish oil.

When at your spot, mix the porridge and the fish oil to a firm consistency and toss in a few balls, these burley balls will break up immediately. The porridge will attract small bait fish, the oil will spread far and wide and attract the fish you are seeking. You can continue to throw the occasional ball of this burley into your swim, I believe you will find it to be quite adequate for your needs.

This is a great way to carry in burley, especially if you have a long walk. It will not thaw and put your car off limits to all but bluebottles, it is mixed at the venue and at the conclusion of your trip, the empty bucket can be used to carry out fillets, just as importantly, you can also wash your hands before leaving.

I hope this helps. It's the principal all serious freshwater anglers adopt to keep fish in their swim. The idea being you wish to attract them, not feed them.

Good luck ... Hangler.