Introduction: (Initial Observation)
Yogurt is a tangy, nutritionally excellent dairy product. Yogurt is a dairy product made from milk. But how is it made? Can we make it at home? How does liquid milk become a solid or viscose yogurt? Does it lose its water to become hard?
Making yogurt project and experiment can help us to answer some of these questions.
Adult supervision and help is required while working with hot material.
Try to find information about making yogurt at your local library and the Internet.
One recipe for yogurt is included at the end of this section.
Yogurt is created from a natural process – the souring of milk in warm temperatures. This makes it difficult to pinpoint exactly where and when it was first produced. As early as the first millennium, the impact of a warm climate on milk was instrumental in the creation of dairy products like butter, cheese… and yogurt.
We do know that early nomadic herdsmen from Eastern Europe were among the first to control this process. The milk from their cows would curdle in the heat, creating a primitive form of the yogurt we buy today. Depending on the temperature and bacteria in the air, different types of curd were made and sold. Making yogurt was also a useful way of preserving any surplus milk as an edible substance.
In Medieval times…
By the 1500s, the healing properties of yogurt were being recognized by doctors. They found that yogurt was an effective aid to digestion and fighting intestinal infections. In France, King François I was prescribed a form of yogurt for this type of complaint. Preserving food by fermentation was developed as a technique and ‘sour’ products like sauerkraut and yogurt became increasingly popular.
At the turn of the century…
Scientists were soon recommending the daily consumption of yogurt. The Russian scientist Ilya Metchnikoff was appointed a director at the Louis Pasteur Institute in Paris at the turn of the 20th century. He worked on isolating the bacteria present in yogurt, discovering that they were responsible for the positive effect yogurt had on human health. Without realizing, he was playing a major role in the promotion of a new concept: food could be good for you.
Despite the efforts of Metchnikoff, yogurt was slow to become popular in the west until midway through the 20th century. It was regarded as a niche specialist food and many were put off by the distinctive sour taste caused by the lactic acid in the mix. Heavy promotion by the dairy industry boosted its popularity, as did the introduction of fruit syrups. They made yogurt more appealing to the Western palate and its demands for a sweeter recipe.
In the present day…
Yogurt’s appeal is now universal. Consumers demanded variety. From its specialist niche, it has evolved into a versatile snack food, a wholesome product and a sophisticated dessert. Special variations have been created containing live cultures, reduced fat content or extra sweeteners designed to appeal to younger children. It is also regularly used by chefs in many recipes, such as curries, smoothies and marinades.
Yogurt Making Recipe
This is a sample yogurt making recipe after some research and some experiments. You may find other recipes or come up with your own.
Yogurt is made by inoculating certain bacteria (starter culture), into milk. After inoculation, the milk is incubated at approximately 110°F ± 5°F until firm; the milk is coagulated by bacteria-produced lactic acid. Since this process happens gradually, water traps inside a structure of coagulated proteins.
Making yogurt at home is fun and less expensive than buying it. It can be made with ordinary kitchen utensils. Following is the materials and directions necessary for making yogurt.
Any non-pasteurized plain yogurt contains live bacteria for making yogurt and can be used as starter culture.
For rapid coagulation and a good taste, temperature must be maintained in about 110°F ± 5°F.
1 gal skim milk
10 oz dry milk
Method for making yogurt
- Mix one gallon milk with 10 oz dry milk
- Heat this milk to boiling and cool immediately to 110°F, discard any skin that may have formed on the milk. Heating the milk to boiling kills any undesirable bacteria that might be present and also changes the properties of the milk protein so that it gives the yogurt a firmer body and texture.
- To the entire one gallon of milk, add one cup of warm 110°F starter culture, Mix well but gently. Do not incorporate too much air. If too much air is mixed in, the starter culture will grow slowly.
- Pour milk into clean containers, and cover with lid. Incubate filled containers at 110°F. Do not stir the yogurt during this period. A Styrofoam box with light bulb may be used as an incubator.
- Maintain 110°temperature until the milk coagulates with a firm custard-like consistency (3-6 hours). Then refrigerate. You may keep yogurt in the refrigerator for two to three weeks.
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
We want to know how easy or difficult is making yogurt. Can it be done at home?
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
Variables that may affect the production of yogurt are:
- The preheat temperature and time that may affect killing bacteria
- he temperature in which the culture is added
- the rate of culture to milk
All of the above variables can be studied (one at a time) so we can see how do they affect the quality of the produced yogurt. However in this project we will not test the effect of any specific variable and try to understand the science of changing milk to yogurt.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
Since yogurt is made from milk, it should be possible to make it at home with kitchen utensil.
As I have learned from a yogurt making recipe, I will heat up some milk to boiling temperature, let it cool off to warm temperature and then add a small amount of culture to that. Culture for yogurt is yogurt and I will use one spoon culture for each cup yogurt. After we add the culture, we should keep it warm for about 6 hours.
Materials and Equipment:
Material needed for this experiment are:
- Kitchen utensil such as pan, spoon, cup, etc.
- Some yogurt as starter culture
Results of Experiment (Observation):
What was the result of your experiment? Did you have any difficulties in making yogurt? Did you have to repeat the experiment to get a good result?
No calculation is required for this project.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
Include a list of your references in your report. Following are some web references but you may also find some related books and use them as a reference.