Milk Experiment: Which milk spoils fast?

Erin and Shawnee

G8

1

Table of Contents

1. About me ------------------------------------------------------------------------------------ ( 3 )

2. Abstract -------------------------------------------------------------------------------------- ( 4 )

3. Question ------------------------------------------------------------------------------------- ( 5 )

4. Research ----------------------------------------------------------------------------------- ( 6,7 )

5. Methods, Testing & Redesign ------------------------------------------------------------- ( 8 )

6. Results ------------------------------------------------------------------------------------- ( 9,10 )

7. Conclusion ---------------------------------------------------------------------------------- ( 11 )

8. Bibliography, References, and Acknowledgements ------------------------------- ( 12,13 )

2

1. About me

Erin Oh and Shawnee Hong, who are 8th graders from Korea International School Jeju

Campus are performing this experiment as a team. The objective of our team is to increase

knowledge in both science and real life through this project.

Shawnee is from Uijeongbu, South korea. She has great interest especially in drawing or

making work of art and listening to music. Also, in sports, kick-boxing and basket ball. Erin is

from Mokdong, South Korea, and enjoys spending time listening to music, reading books, or

with friends.

3

2. Abstract

This experiment is designed to test spoilage of three different types of milk(whole milk,

2% milk, and skim milk). Specifically, to figure out whether the whole milk spoils at the same

rate as 2% milk and skim milk. In real life, this information helps to determine whether food is

spoiled or not and how much times it takes for food from expire date to spoil. Along with helps

when going to market and trying to decide which milk to get. Thus, the question, Does the whole

milk has same spoilage rate with skim milk and 2% milk?, would be answered by the following

experiment.

Based on the content, the hypothesis is: If three types of milk are put under the same

condition, then whole milk will spoil first, because it contains more fat, and the independent

variable had been set as types of milk and dependent variable as time(how long each milk takes

to spoil). On the other hand, the result confirmed this to be wrong as skim milk was ahead

compared to other two milks. The skim milk spoiled on third day, whereas 2% milk spoiled on

fourth and whole milk spoiled on fifth day.

Accordingly, for future opportunities, hypothesis is likely not to be only dependent on the

fat content of milk. For improvements, deeper research about food spoilage would be needed.

Additionally, this experiment could been expanded by testing how long cheese or yogurt will

stay uncontaminated under room temperature.

!

4

3. Question

Does the whole milk has same spoilage rate with skim milk and 2% milk?

Variables

Independent variable: Types of milk

Dependent variable: Time, how long each milk takes to spoil

Variables

Control

Temperature and condition.

Hypothesis

If three types of milk are put under the same condition, then whole milk will spoil first,

because it contains more fat.

5

Experimental Group Controlled Variables

Whole milk

Same temperature and expire dateIdentical amount2% milk

Same temperature and expire dateIdentical amount

Skim milk

Same temperature and expire dateIdentical amount

4. Research

! Food spoilage refers to deterioration of the food’s original nutritional value, texture,

color, odor and/or flavor which then come to be detrimental and ineligible to consume. Main

causes includes, microbial spoilage, autolysis, and infestations by insects or rodents, and low

temperature injury(Varieties of Milk). The microbial spoilage occurs by one amongst three types

of microorganisms, yeasts, moulds and bacteria. Furthermore, fungal spoilage and bacterial

spoilage are under this effect. Autolysis is the breakdown of plant or animal tissues due to action

of enzymes contained in tissues. When foods are spoiled due to one of those causes, changes like

color and odor enables us to make decisions using our naked eyes.

Especially, for milk, there are two types of bacteria, lactic acids and coliform, which

leads to physical and chemical changes on milk. The expiration date on milk is simple estimates

of milk shelf life. Thus, it depends on ourselves to determine whether it is drinkable or not.

Usually, there’s sour smell and curdling, but milk can be sour and not to be spoiled. Those can be

result of fermentation which is a product in the manufacturing of cheese or yogurt. It makes us

hard to exactly figure out spoilage. In addition, the growth rate of bacteria is not much disparate

among milks.

Any variety of milk should be stored under about 7.2°C, otherwise bacterias would

initiate its growth. From the day milk has come from cow, it stays good until around for 14 days.

This date has been extended using the method of pasteurization invented by Louis Pasteur in the

mid-1800s(Rushing).

6

There are three major types of milk: whole, skim, and 2%. Primary distinction between

them are the fat content. The whole milk is standardized to have minimum fat content of 3.5%,

skim milk have fat content along 0-0.5%, and 2% with 2% of fat content(Yu).

7

5. Methods, Testing & Redesign

Materials list

‣ Whole milk

‣ 2% milk

‣ Skim milk

‣ 3 drinking glasses

‣ Magnifying glass

Experimental Procedure

1. Pour the whole milk, 2% milk, and skim milk in 3 separate 250ml beakers. Label each

one to know what kind of milk is in each.

2. Set beakers at the table of room temperature.

3. Observe what happens everyday and document any changes.

4. When milks start to spoil, record the time for each of them.

5. End experiment after the clear spoilage of one type of milk.

6. Pour out the milk and clean beakers.

8

6. Results

Description of changes throughout each day.

Data Analysis

9

Day 1 Day 2 Day 3 Day 4 Day 5

Whole Milk

2% Milk

Skim Milk

No changes and showing consistency

No change in color, but slightly

smells sour

Thins white layer is formed

around the surface,

smells sour

White layer become thicker

White layer turned into

curdle

No changes and showing consistency

No change in color, but

smells sour

Thin white layer is

formed on the surface, still

smelling sour

Surface stars to curdle

Some curdling can

be seen

No changes and showing consistency

Thin white layer is

formed on some parts of

surface, smells sour

Starts to curdle, smells

more sour

There are some yellow curdling on the surface,

smelling sour

More curdling are

being formed

0

1

2

3

4

5

Whole 2% Skim

Whole 2% Skim

Discussion

As time passes by, all three milk started to first smell sour, thin white layer formed on the

surface, and lastly had curdling. Until the second day, smell and layer were only parts to be seen.

However, since the third day, skim milk had curdling, which means that it began to spoil.

According to my experiment, the skim milk spoiled the first, at the third day. Other two

types of milk, whole and 2%, spoiled at the fifth and fourth day, which was one or two days later

than it. One clear fact proved by this result is that as the milk contains less fat, it spoil fast, or its

opposite.

10

7. Conclusion

! Overall, through the experiment, answer to the original question has been made which is:

skim milk spoils faster than the whole milk. It took 5days for whole milk, but skim milk was

faster by one day and started to spoil at day 4. The hypothesis was: If three types of milk are put

under the same condition, then whole milk will spoil first, because it contains more fat.

Consequently, experimental results do not support it. Unlike the hypothesis, milk with high fat

content stays longer in room temperature. This implies that it is more effective to purchase high

fat content milk, the whole milk, which would extend the date(s) of storage. Hence, now it is

possible to apply this result further to see whether there would be difference in which brand of

milk to choose or to discover spoilage of each kind of milk.

In the future, If we get opportunity to perform this experiment again, new hypothesis is

likely to be built in a way that does not rely on the fat content of milk as it is proved to be not an

important factor in determining spoilage of milk. Additionally, to make improvements,

decreasing the checking intervals and development in checking the production of bacterias would

be essential, because it was hard to be sure if the milk was spoiling or actually fermenting.

11

8. Bibliography, References, and Acknowledgements

Acknowledgements

Thanks to Mr.Oren, who provided materials and answered questions related with this

project, and other students for giving advices and help.

12

Works Cited

Rushing, J.E. "Protecting the Safety of Milk." Protecting the Safety of Milk. NC State University,

05 Apr. 2014. Web. 05 Apr. 2014.

"Varieties of Milk." Varieties of Milk. The Dairy Council, 2014. Web. 05 Apr. 2014.

Yu, Leung Chun, Tam Kin Wai,, and Yu Chi Wai. "Spoilage of Food." Spoilage of Food. N.p.,

n.d. Web. 02 Apr. 2014.

13