South Jordan Police Cpl. Sam Winkler says the 67-year-old woman was eating at Dickey's Barbecue Pit on Sunday when she poured herself a glass of tea from the beverage bar.
Winkler says the woman took a sip and her mouth started burning.
She was taken to University Hospital with severe burns in her mouth and throat.
Investigators determined the chemical was 67 percent sodium hydroxide, also known as lye. It's used to clean grease from fryers.
Police are trying to determine how the lye ended up in the tea. Winkler tells KSL the incident appears to be an accident, but police aren't 100 percent sure.