Hi.. Can understand your concern.. As per your complain swollen parotid gland which is the major salivary gland in which the swelling increases when eating anything sour indicates that it is due to obstruction in the duct of salivary gland. The obstruction of the ducts of salivary gland occurs due to formation of crystalline stones composed of minerals present in saliva and is known as SIALOLITH... This leads to obstruction in the flow of saliva and leads to back flow of saliva in the glands and gets accumulated there leading to distension of gland and appears as swelling.. When you eat sour food it leads to stimulation of the glands and saliva production increases and when the saliva cannot flow into the mouth due to obstruction the back flow increases leading to increase in swelling.. I would suggest you to consult an oral pathologist and get evaluated and in case of sialolith locating the stone by taking an x ray or C.T SCAN or Ultrasound and removal can provide relief. In case of small stones can be removed by dentists by massaging over the stones once located and pushing them out from the duct opening.. Large stones needs to be removed by a small incision made in the mouth near the location of the stone and is removed Hope your query is solved.. If you find the answer helpful please write a positive review and click on find this answer helpful as a token of appreciation.. Thanks and regards.. Dr.Honey Nandwani Arora.