Friday, July 11, 2014

Making yogurt.

I make my own yogurt.  I don't have a special reason to.  In New York State we have some sort of weird milk pricing system that makes milk almost as expensive as yogurt.  But it's fun to make your own, it's easy, and you can control how it comes out.  In addition to resulting in delicious yogurt it's a good experiment for young kids to teach them about microbes, fermentation, and experimental observation.

The complete instructions are below, but here's the TLDR version:

Heat milk to 180F.  
Quick-cool it to 120F. 
Mix in a little bit of room-temperature yogurt.
Store for six hours anywhere from room temperature to 120F.  Lower temperature equals sweeter, thinner yogurt, higher makes more sour, thicker yogurt.
Sample the yogurt and store for more time if desired.
Strain the yogurt to thicken as desired.

My highly sophisticated cooling bath.  

What You'll Need:

1/2 gallon milk
A thermometer (preferred)
3 tbsp of your favorite yogurt, as long as it has "active cultures" written on the container somewhere
A saucepan of at least 4 quarts
A whisk
A ton of ice
A vessel large enough for an ice bath
A container for the ice bath if you can't put your saucepan in it
A measuring of at least 1 cup, like a Pyrex Prepware Measuring Cup
A spoon
A 1/2 gallon container for your yogurt, or preferably 2 one-quart containers (see below).

What kind of milk?

Good milk, but not too good, and of any fat content you want.  I like to get relatively fancy whole-fat milk from grass-fed cows because I like the flavor better but just about any milk will do.   Full-fat, 2%, even 1% are all fine.  I suppose it will work with skim milk, but who wants skim-milk yogurt?   You can use raw (unpasteurized) milk if you want but there's no point since the very first thing we're going to do is heat the milk to 180F -- pasteurizing it.  The one milk you may want to avoid is milk that has been pasteurized at very high temperatures.  It's called UHT milk and some people report that the yogurt doesn't form quite right with that sort of milk.  UHT is common among the health-food crowd, so be particularly careful if you're shopping for a fancier milk (local, grass-fed, etc.).  Shelf-stable milk is also UHT pasteurized.  This discussion is about yogurt from cow's milk, the only kind I've made, but it will work equally well with milk from sheep or goats.  If someone tries this with a more exotic milk like camels or kangaroos or something I'd love to hear about it!

OK, let's go!

Put 3 tablespoons of your favorite yogurt into a container and allow it to come to room temperature. Place the milk into the saucepan.  If the milk has not been homogenized, make sure the fat gets in there and whisk it aggressively until the fat is fully incorporated.  Heat the milk under medium or medium-low heat until it's 180F (82.5C).  Whisk the milk as necessary to prevent any film from forming on the top or scorching on the bottom.  Milk has a tendency to boil over.  Whisking the milk should prevent this but you're using the larger saucepan just in case. 

The reason to heat the milk is to pasteure (or re-pasteurize) the milk so when you add the yogurt later the microbes (which we'll talk about below) won't have to compete with any others.

As the milk approaches 180F prepare an ice bath. 

One the milk hits 180 you can start to cool it.  There's no need to linger at that temperature.  Transfer the saucepan to the ice bath or transfer the milk to whatever vessel you're using in the ice bath.  Cool the milk to approximately 120F (49C).  A little lower is fine, don't let it stay much hotter.   Then remove the milk from the ice bath.  As with heating the milk, the quick cool-down is intended to give your yogurt cultures a microbial monopoly; you won't want any little beasties which might be floating around your kitchen to get in the milk.

Pull out a cup or so of the milk.  Whisk in the yogurt thoroughly and then stir the mixture into the warm milk.  You're now ready to make yogurt. 

The fun part begins!

You've now got a mixture that for our purposes contains milk and whatever microbes were in the yogurt you choose as a seed.  It's time for some science.  The two main microbes are the bulgaricus subspecies of Lactobacillus delbruekii and Streptococcus thermophilusBoth of these microbes primarily eat lactose, the sugar in milk, and they, well, they excrete lactic acid and other compounds.  The lactic acid both sours the milk and curdles it into the thicker texture you associate with yogurt. There are other microbes in smaller amounts which vary by brand and which will help fill out the flavor profile of your yogurt. 

But.  But that mix of microbes is a relatively small differentiator of your yogurt's taste.  The biggest variables are how long and how hard your Lactbacillus and Streptococcus work.  The longer you leave the yogurt unrefrigerated and the higher the temperature at which you leave it, the more sour your yogurt will be.   Here's where an observational experiment comes in.  Pour the mixture into your two (or even three!) containers and cover them.  Put the first container into a reasonably warm cabinet in the kitchen.  Over time the yogurt will cool to the cabinet's temperature.  Leave it for 6 hours or so.  The other container you want to keep as close to 120F as possible and leave that for 6 hours, too.  If you have a third, keep it at around 105F, again for 6 hours.  

How do I keep these things warm?

Many ovens will have a setting to keep something warm, right around 100F.  Sometimes it doesn't involve anything more than turning the light on and leaving the oven door ajar.  To keep the yogurt at 120F, I fill a cooler with water at that temperature, lower the container into the water and close the cooler.  A cooler of even moderate quality should keep the water warm for enough time.  If not, pour some hot (140F) water into the cooler every couple of hours to maintain the temperature.  Make sure the temperature doesn't get too far above 120F or you risk killing the bacteria. 

Time for tasting!

Sample your yogurts.  The room-temperature yogurt should still be fairly runny but still recognizably yogurt.  It will have a lot of lactose left over and be fairly sweet.  The 120F yogurt should be fairly thick and almost as sour as sour cream.  In fact, I use 120F yogurt as a sour cream substitute.  The 100-105F yogurt should obviously be somewhere in between.   If you'd like, leave some or all of the yogurt to continue to ferment for a few more hours until it has reached the flavor and consistency which is perfect for you. 

Refrigerate the finished product and enjoy!  When it comes time to make more yogurt, you can use the remainder of the current batch to make the next one.  You can propagate the yogurt indefinitely and it will still be yogurt, but the flavor profile will change over time because you don't have the controls that your favorite yogurt company does.  If you like the changes, you're in luck.  If not, every few batches buy some yogurt and start from the beginning. 

Going Greek.

If you prefer a thicker, Greek-style yogurt, pour your finished yogurt into a strainer lined with a couple of layers of cheesecloth.  Place a bowl below the strainer and put the whole contraption in the refrigerator.  Stir the yogurt every hour or two until it's reached the perfect consistency for you.

The liquid which drains is whey and is delicious and nutritious as a water substitute in any baked goods, soups or for cooking pasta or soaking or cooking beans.  

And there you go.  

Customized yogurt exactly as sweet or sour and as thick or thin as you want.  Perhaps you'll want to have different yogurts for different purposes.  Say, a thick sweet yogurt for parfaits and a sour thinner one for tzatziki. It takes a lot of time but very little work.  

This post contains one or more links to an affiliate page at  If you make a purchase though the linked page I will receive compensation from Amazon. This is a scheduled post.

1 comment:

  1. I don't know why, but your photos are showing up for me anymore. Maybe it's because I've moved and have switched to a new IP? I'll try to remedy the situation :)

    Mmmm... yogurt. It might just be my favourite food, if not, it's certainly near the top of my (as yet nonexistent) list. And, speaking of my move again, I'm not able to buy my favourite (Canadian) yogurt in this province! Wah! It's been many years since I made my own yogurt, but maybe I'll try again.

    Oh, huh... I'm not able to sign off as Peeking Duck anymore, either. Well, now you know whom this "Anonymous" is :)


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