Milk Spoilage Poster

Abstract

In many secondary schools today there is a great need to focus, or hook, students' attention on a particular subject. One way to do this in a middle school is to use a poster that is both informative and humorous. An interesting poster that is followed by questions can get students' attention and interest effectively. The poster followed by questions and answers with students makes the lesson student-centered rather than teachercentered. We have made a poster on milk spoilage for a middle school life science class. This idea can be adapted for elementary school or high school introductory biology classes. Our poster illustrates milk spoilage in cartoon form. Mr. Lactose smiles at milk kept in the refrigerator (pH = 7.0), and he cries when milk is kept at room temperature (pH = 4.0). Also, when milk is at room temperature, Mr. Lactose has a vision where Streptococcus, Lactobacillus, Escherichia coli, Bacillus bacteria and yeasts spoil milk. Milk is an ideal medium for bacteria. Bacteria have an important role in milk's freshness and spoilage. Most bacteria in milk are killed through pasteurization, however, some remain. Milk kept in a refrigerator will be reasonably fresh for seven to ten days. Milk spoils after one to two days if kept at room temperature. Milk spoilage is a result of the metabolism of lactose (milk sugar) into lactic acid that causes the acidity of milk to increase. The pH of fresh milk is about 7 and of spoiled milk about 4; this increases somewhat in the later stages of change. A demonstration of milk chemistry will enhance the poster idea. Demonstration: Before Class Preparations