We make salmon fish cakes from a mix of canned fish, cooked potatoes and eggs mixed in a food processor. They are then deep fried. We find that the first batch are fine. The second batch comes out much looser and parts can even break off in the frying. Why is this and what can be done to stop it?
In order to get fried cakes to stick together, they want to be cold when they go in to the oil. This allows them to congeal so that they are more solid. If you are leaving your ingredients out while frying or if there are warm ingredients giving off steam, this could explain the slow degradation with each batch. Once they're done in the food processor, put them in the fridge (or freezer) to cool them. Pull out just enough for a single batch at any one time.
Also, it is possible that over time (by the time the first batch is done), either the oli is not hot enough or its too hot and causes them to disintegrate!