Starch

It's difficult to product strong pellets from starch rich ingredients.
Starch glue property become active in high temperature and high humidity. Gelatinized material functions as lepiszcza and helps to achieve expected quality of pellets. Important: if for any reason natural starch contained in feed is gelatinized we should expect worse quality of pellets.
Example is cereal grain drying in high temperatures, which causes pre-gelatinisation.

Moisture (humidity)

Sometimes it's necessary to add some moisture before pelleting process for good quality of product. Many of actually used ingredients are very dry and besides added moisture we should add steam, especially when earlier moisture was absorbed before mixture get into conditioner.

Binders

When expected quality of pellets can't be achieved nor by steam conditioning or using proper matrix we can use bonds. Two of usually used are: bentonit, lignin sulfate. Using of lepiszcza is expensive so should be the last solution.