Hey, there’s SCIENCE in my

YOGURT!Or… how to make life science

more interesting!

A little bit about me…• Ag Science teacher at Zane Trace High

School near Chillicothe,Ohio• In a two-teacher program, so I specialize

in the “science” side of agriculture education by teaching Food Science, Ag Biology and Animal Science courses

How’d I get this idea?• Science Fun With Dairy Foods 4-H Project

– Ohio Cooperative Extension Service Pub 490– One of the assignments was to make yogurt– Never had Ag class in HS so, when I started I

used a lot of my 4-H books for resources– Lesson went really well, kids liked it, I’ve

repeated it every year since then

Yogurt making today• Today yogurt is one of the most popular

dairy foods we eat!• Go-gurt, smoothies and new flavors make it

more convenient to eat• Marketed to MANY different groups (kids,

teens, athletes, probiotics for immunity, etc)• Many ethnic groups eat yogurt with food

– Indian, greek, middle eastern

When to teach this…• It fits in lots of different subjects, but I

usually do this lab at the beginning of the year with my Freshmen to get them excited, then later in the year with other classes.

• This lab can be extended to fit just about any agriculture class – more about that later…

Getting ready…• Most of the items you need can be

purchased easily or found around the shop• You’ll need a way to heat the milk and

store the yogurt after incubation period – I’ve used the consumer sciences lab before– Portable burner and fridge in teacher’s lounge

is good too.

Gathering suppliesThe rest of the stuff you need can be picked up

at your local grocery store (I like Kroger)

*1 gallon of Milk (you’ll have enough for 4 batches with a gallon)

*1 carton PLAIN yogurt (again, this is enough for 4 batches)

*Plastic containers (Glad ware is awesome!)

*Saucepan (hit a yard sale and get one cheap)

*Wisk*Candy Thermometer

How to introduce to students…

• Depends on your subject…– Ag Bio = what do living things need to grow? also, intro to scientific method & biotech- Food Science = product development, sensory

evaluation, nutrition label calculation, dairy foods- Business = marketing, product development,

advertising campaign- Animal Science = Dairy cattle and products

What does it cost to make it?• Milk (whole is best!)

– Bought at Kroger for $1.98• PLAIN Yogurt with live bacteria

– Bought at Kroger for $2.99 – Dannon brand• Candy Thermometer = $3.99• Plastic Tubs = 6 for $1.99 (could be free if you saved them)• Saucepan - $1.00 at yard sale• Whisk – 25 cents at yard sale• 5th burner hot plate = $2.00 at yard sale• Incubator (someplace to keep it warm) – free bag from

National Convention!• GRAND TOTAL for 4 classes = $14.20 Whatta deal!

History of YOGURT• Thousands of years ago shepherds used

dried out sheep stomachs to store milk.• A certain bacteria that lived on grass was

still living in the sheep stomach when milk was put in it.

• That bacteria changed it’s behavior, fed on the sugar in the milk, turning it into YOGURT!

Questions to Ask…• Is this Biotechnology? • How is yogurt made today?• What kind of bacteria are needed to

make yogurt?• What conditions do the bacteria need in

order to grow?• What changes occur in the milk as it

becomes yogurt?• How do companies like Yoplait and

Dannon make new varieties of yogurt?

Steps for yogurt1. Measure out 4 cups of milk and heat to

161 degrees F– Kills harmful bacteria (Pasteurization)– If we didn’t do it, harmful bac could grow– Don’t HAVE to do this if milk is already

pasteurized, but I do just to show the process2. Place the pan of hot milk on a bucket of

ice to cool it to 115 degrees F quickly– Keeps bacteria in air from contaminating milk– 115 degrees is good temp for yogurt making

bacteria to grow in.

Steps for yogurt 3. Add in 1 cup of PLAIN yogurt with ACTIVE

CULTURES– This introduces yogurt making bacteria to the milk.

Lactobacillus bulgaricus, Streptococcus thermophilus

– They will “eat” the LACTOSE (sugar) in the milk and produce LACTIC ACID as a result.

– This process is called FERMENTATION– The ACID will cause the protein in the milk to

DENATURE or thicken.– The ACID makes the milk SOUR and the denatured

protein makes it THICK

Steps for yogurt4. Allow the yogurt to sit in a warm place

(over 100 degrees) for 5-8 hours– This gives the bacteria time to grow and eat– Longer time = more sour, thick yogurt– As soon as you put it in the fridge, the

bacteria stop growing.

Steps for yogurt5. Take out yogurt the next day and let

students go crazy with it!-You can provide items to flavor yogurt with or make them bring their own.-Make sure they measure items if they plan to calculate nutrient info later…-Conduct sensory evaluation when finished – have them “grade” their flavor

Extending the lesson…-Allow “Do-overs” with yogurt varieties-Experiment with variables such as:

-Incubation time-Whole vs 2% Milk-Using culture vs yogurt to produce-Using different incubation methods

-Create marketing plan, packaging, nutrition label, etc. for variety created.

-Ask “what if” questions afterwards…

And Now, a word from my students!

Three video clips from my Freshmen Ag Bio classes on the day that they made and tasted their yogurt varieties.

See if you can guess which class is the one that meets right after lunch period!

More Info? Sure!For those of you who use AgEdNet.com…

-FS 111 – Fermentation in Food Production-FS 113 – Dairy Foods-FS 001 & 002 – Nutrition Labels lessons-LA 189 & 190 – Milk & Milk components lessons

New England Cheesemaking Company-www.cheesemaking.com

-if you want more info on ordering culture,etc

Yogurt Making Website w/videos!!-www.makeyourownyogurt.com

Thanks so much for listening!!

Good luck making your own yogurt!If you have any questions, just drop me an

email at:jmoore@mail.gsn.k12.oh.us

This presentation will be on the Zane Trace school website: www.zanetrace.org