To be honest, whilst I've played around with particles over the years, a mixture of Hemp and Maize, soaked and boiled in just water and used within a day or so, take some beating. Maybe a little hemp oil mixed in.
I agree with Law about salt, a bit of human grade Rock Salt or Calcium Chloride in the spring can help, after May though, never noticed that it made a hapenth of difference. I've found it more effective to put a small PVA stick of salt on the hook rather than mix it in the particle.
Tigers need to be allowed to go gloopy, which means letting them ferment a while.
The 'French Mix' type (groats, flaked maize, crushed hemp, patiblend + whatever takes your fancy) does improve with a week in the bucket to allow the 'milk' out of the groats and the oils to diffuse. A bit of sugar or mollases helps get it going.
Most of the additives I've tried have added more to the cost than the effectiveness.
Just a comment on effectiveness, they aren't the answer to the perfect bait but intelligent use of them as a ground bait does create a safe feeding zone, it attracts smaller fish to feed which in turn attracts the carp, get it right and they really get their heads down. Bait can either be particle or boily over the top. Pellet can achieve the same but to get a similar effect using just boily would cost a fortune.
Stu