Guided inquiry is the practice of allowing students to come to their own conclusions about a set of data instead of verifying a known result using a given experimental procedure. Open inquiry takes this idea one step further by allowing students to develop their own experiment and then analyze the data to arrive at a conclusion. To expose upper level undergraduate students to the concepts of experimental development and the research thought process, a safe but thought provoking and relevant set of experiments was developed, combining guided inquiry and open inquiry teaching methods. Two guided inquiry experiments have the students quantify the amount and types of sugars present in fresh milk, spoiling milk, and lactase-treated milk using DNS reagent (dinitrosalicylic acid) which detects all reducing sugars and a glucose oxidase-peroxidase assay to determine glucose only. This leads into open inquiry experiments where the students develop their own hypothesis and test various aspects of the chemistry of the lactase enzyme, the chemistry of milk spoilage, and other means to determine the content of sugars in milk. Some of the more common student derived experiments are presented such as using different sugar standards in the DNS assay and testing the activity of lactase at different temperatures and pH.