[Ellie May]

I really don't know what it could be.
Homecooked food should not be left out for more than one hour.
You could just put it in the fridge and keep pullilng it out and trying.
I know I am in the minority but I think if a dog really doesn't like something, he/she shouldn't have to eat it (within reason...unless they are REALLY picky and don't like anything healthy).

Itching is the major symptom of food allergies (ears and biting paws).
Not all dogs are allergic to beef, so I wouldn't worry about it unless you see symptoms.
You could also try lamb, fish, venison, egg...
Just be careful how much fat and grease you are giving.
I prefer not to fry foods because I think they just come out way too greasy (for Ellie at least).