Sodium hydroxide (NaOH), commonly known as lye or caustic soda, doesn't *turn* grease into anything. Instead, it reacts with grease (which is primarily composed of triglycerides) in a process called saponification.

Here's what happens:

1. Hydrolysis: The hydroxide ions (OH-) in NaOH attack the ester bonds within the triglyceride molecules.

2. Formation of Glycerol and Fatty Acid Salts: This breaks down the triglycerides into glycerol and the corresponding fatty acid salts.

3. Soap Formation: These fatty acid salts are what we know as soap.

So, the end result of the reaction between sodium hydroxide and grease is soap and glycerol.

This is the basic principle behind soap making, where fats and oils are treated with lye to produce soap.