I have a restaurant though I'm not a professional chef. In my restaurant we are planning to introduce onion rings with breadcrumbs as sides. Many recipe I found egg in batter but am confused the egg will get spoilt once we keep aside after frying a portion of onion ring. Please help me to find an alternative to deliver onion rings as fast as we are fast food restaurant?
Something you might want to consider is to use your batter that you have and bread your rings and put on on parchment paper (not touching each other) and freeze. Once frozen they can be consolidated. They can be fried frozen. We did this at a hotel restaurant and had great results. By doing this you can prepare only the amount of egg mixture as needed.
I will share with you a recipe that does not even use eggs or milk. Using a slicer slice the onions thin and put in ice water. Toss rings in a seasoned flour and fry. Easy, and quite good. You will have to experiment on breadcrumbs if that is what you feel you really want to do.
A batter recipe that we made in a restaurant, had beer, flour, salt, and pepper. the more flour you used in the recipe the breadier it would be to the contrary with less flour you would end up with a crispier texture but less coated. First you would need to dredge the onion rings in flour. If fried and not eaten immediately it will get soggy. I've only seen people freeze breaded food but if it works for batters I would definitely give it a try. I have also seen cooks add cornstarch 1/4 ratio to 3/4 flour and instead of beer they would use mineral water. And these recipes can be stored roughly 3 hours on the fridge. Test and Taste good luck.