If fishing a Stillwater or canal, I would have thought mashed bread would be to filling for roach fishing,
Depending on the weather I use liquidized bread that has been frozen, liquidized, and sieved a few times so it is
as fine as possible, that way you get the attraction but less filling,add hemp if required but not to much or there
is a possibility the fish get preoccupied with it, don't be tempted to keep topping up when using bread,
you can be fishing for bites not fish, either pinkie or bread punch or Small piece if flake on the hook, I use the Drennan Flake Punches as well as the bread punches, If using corn a good tip is to squeeze the centre out and lightly
hook the skin, this creates a slower sinking bait, again with the attraction but not as filling.
You will get other responses to your question, some may be the same and some will differ, everyone has their own way of doing things and working out the best way to do them,
If you fish a river I would use mashed bread, that way you have a chance of catching chub as well.
I think your question is more suited to pole fishing or short range waggler fishing, liquidized bread can both be
potted in and thrown gently with a slight squeeze to hold it together.