What Causes Persistent Regurgitation Of Food?

After eating a teaspoon of white instant rice, his esophagus shuts down so that no food or drink will go down. He reguritates non stop for an hour and just salivates and even that he can't swallow. Symptoms stop after about an hour. What do you think causes this. It only happens occasionly , but when it's only rice and not a very large amount. Is this an allergice reaction? He never breaks out in hives or reactions anywhere else.