how to: make yogurt

If there's one thing that I know how to do, it's grow bacteria. After all, that's what I do 40 hours a week when I'm not making delicious food and crunching grocery numbers. I work in lab where we have big fancy incubators and special nutrient rich agar to give the bacteria the perfect environment to grow. But guess what? It's not really that complicated.

To make yogurt, you just need to complete a few simple steps:

1. Heat some milk to 180 degrees Fahrenheit to kill any rogue bacteria.
2. Let the milk cool down to a temperature that bacteria like (115 degrees Fahrenheit).
3. Inoculate the milk with the bacteria that you want (lactobacillus).
4. Let the milk incubate and a nice warm, cozy temperature while the bacteria reproduce and work their yogurt magic.

As the lactobacillus feeds on the lactose (milk sugar) it produces acid, which not only gives the yogurt it's nice tangy flavor, but it also denatures the proteins in the milk, which solidifies the mixture (just like when heat denatures the protein in egg whites and they turn solid).

There are many methods for heating, cooling, and incubating milk to make yogurt and the method I'm describing here is just one.

Some people like to heat, cool, and incubate all in their slow cooker, but that can add about 5 or 6 hours to the process, so I heated my milk on the stove top. I used the slow cooker solely as an incubator (not plugged in) because it has a nice, thick ceramic lining that holds heat well. All in all, it was super easy and I think I will be doing it again!

And does it save money? Yep! A regular six ounce cup of yogurt usually costs around $0.60 each. When I buy a 32 ounce container, that same 6 ounce portion costs me about $0.41 cents. When I make it from fresh milk, a six ounce portion costs me $0.29. Not bad!

Homemade Yogurt

Total Recipe cost: $2.58
Servings Per Recipe: 9 (6 ounces each)
Cost per serving: $0.29
Prep/cook time: 1 hr. Incubate time: 8-12 hours Total: 9+ hours

INGREDIENTS		COST
6 cups	milk	$2.17
1/2 cup	plain yogurt	$0.41
TOTAL		$2.58

STEP 1: Bring a large pot or tea kettle to a full boil and pour the boiling water in the slow cooker. Allow it to warm the ceramic and eventually cool to around 115 degrees.

STEP 2: Meanwhile, bring 6 cups of milk up to 180 degrees over medium heat (about 10-15 minutes). Make sure to use a thermometer and stir occasionally to prevent scorching on the bottom of the pot. Once it reaches 180 degrees, turn the heat off and allow the milk to cool down to around 110-115 degrees.

STEP 3: Once the milk has cooled to below 120 degrees, stir in the plain yogurt. Once it's fully mixed in, pour the milk into clean mason jars. Make sure the water in the slow cooker has cooled to around 115, then place the mason jars in the slow cooker warm water bath. Secure the lid on the slow cooker and wrap the entire thing with a towel. NOTE: The slow cooker is never turned on during the entire process.

STEP 4: Allow the mason jars to incubate in the warm water over night (8-12 hours). The longer it incubates the tangier and more gelled the yogurt will be. After incubating, screw the lids on the jars and refrigerate the yogurt until chilled (it will gel further as it cools).

See the bottom of the post for more tips!

Step By Step Photos

The first thing I did was warm up my slow cooker. I poured in enough boiling water to fill it about half way full. Then, I just let it sit there while I prepared the milk so that it would eventually drop down to 115 degrees. If it cools down to 115 before your yogurt is ready to incubate, simply put the lid on to hold in the heat.


Next, pour six cups of milk into a pot and bring it up to 180 degrees over medium heat, stirring occasionally. It will take about 10-15 minutes.


You definitely need a thermometer for this process. A candy thermometer works best, but I quickly found out that my 10+ year old candy thermometer was not working right, so I whipped out my meat thermometer. If using a meat thermometer, just make sure to stir the milk before reading it and make sure the thermometer is not touching the bottom of the pot.


Once it reaches 180 degrees, turn the heat off and allow the milk to come back down to about 115 degrees. This step took me about 40 minutes, but will probably vary quite a bit, so just keep an eye on it.


Now it's time to add in the good bacteria. Take a half cup of plain yogurt and stir it into the warm milk.


Pour the warm milk/yogurt mixture into clean mason jars. Place the jars into the slow cooker with the warm water (make sure the water has also cooled to around 115 degrees).


Secure the lid on the slow cooker to hold the heat in and then wrap with a towel for extra insulation. Let it incubate for 8-12 hours.


After incubating, place the lids on the jars and refrigerate until cooled. After eight hours my yogurt was only slightly tangy, so next time I think I'll let it go longer - and I'll update you too!


The first scoop of yogurt was nice and firm, like in the first photo, but upon stirring it does become quite loose. Almost to the point where it is pourable. Before stirring it, it is so gelled that I could turn the jar sideways and it would not move.

TIPS:

• Higher fat content milk works the best and makes the thickest yogurt. I used 2% milk and it worked pretty good.
• For added thickness, stir in either dry milk powder, or a packet of gelatin when you stir in the yogurt starter (at the 115 degree stage).
• Sugar and vanilla can also be added in at the 115 degree step for a sweet vanilla flavor.
• The first time you make yogurt, you'll need store bought plain yogurt as the bacterial "starter." From then on you can just use the last 1/2 cup of your previous batch!
• Homemade yogurt will stay good in the refrigerator for about two weeks.
• To turn this into thick Greek style yogurt, line a colander with a coffee filter, scoop the yogurt into it, and then place it over a bowl and let it drain in the refrigerator until it reaches your desired level of thickness.
• To make the yogurt in the slow cooker from start to finish, pour the cold milk directly into your slow cooker, turn the heat on to low and let cook for 2.5 hours. Turn the heat off and let rest for 3 hours (this brings it back down to 115 degrees). Stir in your yogurt starter, wrap the slow cooker in a towel, and incubate for 8-12 hours.

I can't wait to experiment more with this recipe and I'll be sure to update the post with any tips or tricks that I learn. If you're an avid yogurt maker, feel free to share your methods, thoughts, tips, and opinions in the comments below!