Tuesday, July 31, 2012

Yogurt: Simple complexity or complex similicity?

It's hard to imagine anything much simpler than yogurt:  basically, it's sour milk.  People have been making it for millennia without the benefit of elaborate equipment.

If you want to make yogurt, there's not much to it:  add some yogurt to some warm milk and keep it warm long enough for it to turn into yogurt.  That's it.

Unless, of course, you want consistent, reliable results (and you know me, I want consistent, reliable results!).  Because here, you see, is the rub. There are about a million variables:  what kind of milk?  what starter?  How warm should the milk be?  Should you heat it to a relatively high heat and let it cool, or just warm it to the temperature you want?  How long do you let it incubate (the fancy term for letting it sit there until it's done)?

Most people don't worry about all of this.  They just go to the grocery store, buy a couple of tubs of something and eat it, probably while they're heading out the door in the morning.  The thing is, Sue has eaten yogurt for breakfast for years, and I began doing so religiously about three years ago.  (I had eaten it on and off ever since I met Sue.)  With both of us eating yogurt daily, we were going through quite a lot of it.  At one point, we were in Maine, where they don't recycle the kind of plastic yogurt comes in these days, so we were throwing away oodles of plastic.  That rankled.

So I bought a yogurt maker and began the quest for (my) perfect yogurt.  I've pretty much got it down, but you might want your yogurt to be different:  less creamy, more creamy, more sour, less sour--you get the idea.  Even so, my method has to vary depending on external factors:  even the ambient temperature of the room seems to have an impact.

Here are the considerations:

1.  What kind of milk? 

Any kind will produce yogurt, but the yogurt will be different depending on the fat content--that's the biggie.  Other considerations are organic or not, and even the brand of milk can make a difference.  When you find one you like, stick to it.  You'll get the most consistent results that way.  We like organic 2% milk.  (And though the hippie in me would like to think otherwise, I don't think the organic bit is actually what matters.  Most organic milk is ultra-pasteurized, and I think the high heat affects the proteins.  This, I suspect, is why yogurt made from organic milk is different from that made with your ordinary, garden variety milk.)  Some procedures call for adding dry milk.  I have tried this and didn't like the result.  The typical amount of dry milk is usually about 2 - 4 tablespoons per quart of liquid milk.  Use the larger amount if you're using instant dry milk--by far the easiest thing to find.

2.  What kind of starter?

You need a commercial yogurt that advertises that it has "active yogurt cultures."  This means that the little guys who ferment the milk--I fondly call them yogis--are alive and kicking.  You must use plain yogurt as a starter.  Choose a commercial yogurt you like and that is closest to the way you want yours to come out.  (But know that other factors, such as incubation time, will affect the results, so the starter isn't a guarantee that your yogurt will be like the stuff you buy.)  I have successfully used Stonyfield, Fage, and Chobani.  Once upon a time, I used to use Danon.   Note that Fage and Chobani are Greek-style yogurts.  They are very thick and creamy because some of the whey is strained out after the yogurt incubates.  If you make yogurt from them but don't strain it, yours will be thinner than the starter.

3.  How to heat the milk?  To what temperature?  How long does it have to stay at temperature?

You can successfully make yogurt by heating milk to about 110 degrees F and adding the starter.  Because modern commercial milk is pasteurized, there is less risk than formerly of there being stray bacteria in the milk that could interfere with fermentation, so heating the milk to a higher heat isn't strictly necessary.  Yogurt made from milk that has been heated to 110 will take a long time to incubate (as much as 12 hours) and will tend to be runny.  It will also be on the tart side.

Most instructions tell you to heat the milk to 180 degrees F.  This will kill off anything that shouldn't be in there, on the off chance that there's something that isn't yogi-friendly swimming around in your milk.  If you do it this way, you need to cool the milk down before adding the starter.  Anything hotter than 110-115 risks killing the yogis.  Very bad.  (If it's too cold when the starter goes in, it's also likely to be a flop.) Yogurt made from milk heated to 180 will take a little less time to incubate than the previous method--perhaps 8 hours.  It will still tend to be runny and tart.  The dry milk some methods call for is an attempt to get a better, firmer texture for the yogurt.  I find that longer cooking solves this better, so read on.

I like my yogurt smooth, creamy, and only moderately tart.  I especially don't like it when the whey separates from the yogurt in the jar--you know, that watery looking stuff that floats around the top and edges after you spoon yogurt out of the container.  I learned that keeping the milk at a higher temperature for a longer period of time (20 - 30 minutes) alters the proteins.  This means that the yogurt will incubate faster and will have a firmer texture.  Because it will incubate quickly, you can stop it before it gets too tart.  This is my preferred method.  I bring the milk to 180 as quickly as possible, hold it there for for 20 or 25 minutes, then cool it quickly (details about all of this further down).

4.  How to incubate it? 

I've seen instructions for things as low-tech as putting the milk and starter into a thermos and letting it stand overnight.  A time-honored tradition is to put the yogurt into a gas oven with a turned-off pilot light or on top of the gas stove near the pilot light.  (I have an electric stove, so this isn't an option for me.)  You need something that will keep the yogurt at a fairly constant 100 - 110 degrees F--I think 108 is the optimum.  The easiest way to achieve this is with an electric yogurt maker.  It's a simple appliance:  it has a heating element and a thermostat in it so that it keeps things at a nice lukewarm temperature.  You set the jars in it (some use small, individual-serving jars, others make a whole quart in a single container), cover it, and walk away for a few hours.  Many yogurt makers have a timer that will turn the machine off when the yogurt has incubated for the time you've chosen.

5.  How long should it incubate?

Ah.  This is the 64-dollar question.  Basically, the longer you let it go, the more tart it will be.  So you want it to go long enough that it congeals--I think the correct word is "clabbers"--and then you go as much beyond that as you need for the yogurt to be as tart as you like.   Once you've stopped it, you need to refrigerate it for several hours before you eat it.

6.  OK, enough theories.  How do YOU do it?

I thought you'd never ask.

I do have a method that I employ pretty consistently, but even this requires tweaking from time to time.  What works perfectly in Arizona doesn't yield the same results when we're in Maine for the summer--doubtless because of differences in the milk and the ambient temperature in the room.  Some of what I do is based on quirks in my yogurt makers.  I'll explain all of that along the way.

My machine makes up to 14 6-ounce glasses of yogurt.  So the amounts I'm giving here are based on that yield.  You could cut it down proportionately if your machine doesn't hold as much.  I recommend making small batches at first until you get the results you want.  And don't be afraid to make notes.  There are a lot of variables here.

HEATING THE MILK:  For 14 6-oz. jars, I start with 5 pints of milk.  (That's a half-gallon, plus another 2 cups; 10 cups in all.)  I use organic 2% milk, but I've also used 1%.  In Arizona, where I have a relatively new stove that can heat quite gently and evenly, I put the milk into a 5-quart stainless steel pot and set it directly on the stove.  I set a digital thermometer into the pot and turn the heat to high.  Then, stirring constantly, I watch the temperature carefully.  As it approaches 180, I turn the heat down to about medium, start a timer, and stir, adjusting the heat as needed to keep it between 180 and 190 for 20 minutes.  You read that right:  I end up stirring the milk for about half an hour.  It's worth it for the taste and texture of the yogurt.

My stove in Maine is less reliable, so here I use a double boiler.  I have two 5-quart pots that nest into one another a bit.  I put about an inch-and-a-half of water into the slightly larger one, set the slightly smaller one on top, add the milk and rig up the thermometer.  Then I turn the heat to high, adjusting it as needed and keeping the temperature between 180 and 190 for 20 (lately 25) minutes.  There's a plus to the double boiler method:  while you still have to monitor it closely to maintain a steady temperature, you don't need to stir it constantly.  An occasional stir will do.

A note on thermometers:  I use a probe-type thermometer like the one in the picture.  It has a clip that goes on the side of the pot, and you set the probe in the clip--being careful the tip is submerged but not hitting the bottom of the pot.  This then plugs into a little box that sits on the counter and reads out the temperature constantly.

Keeping the temperature steady is easier said than done.  Over time, you learn just when to turn your burner down so that you don't go too far past 180.  You learn how low to turn it so that it doesn't dip too far below 180, and you learn when to jack it back up for a little while.  Be patient.  You will get better at this!

ADDING THE STARTER:  I set the pot--with the thermometer still attached--into ice water.  I usually fill the sink to a depth of an inch or two with ice water and set the pot in it.  In Maine, where the sink is big, I find a bigger pot that will hold the milk pot and a good supply of ice water.  I stir it occasionally and watch the temperature closely: it takes about 10 minutes to cool.  For the starter, I use 2 6-oz containers of Chobani these days.  I used Stonyfield for a long time, and that works, too.  You can theoretically make new yogurt from a couple of glasses you've saved from the previous batch.  I worry that the yogis will start to mutate or something, so I always buy new yogurt for each batch.  I pull the starter out of the fridge right when I start measuring and heating the milk--that way, it won't be ice-cold.  While the milk is cooling, I put the starter into a 1-quart measuring cup and stir it up until it's smooth.  When the milk cools to 115 degrees F, I immediately pull the pot out of the cold water.  (Watch the milk closely, especially when it gets down around 125:  it will go fast from there.  Don't let it go below 110 or you risk a failure.)  With a ladle, I put a scoop or two of the warm milk into the starter and stir it up.  This thins the starter so that it will combine thoroughly with the milk.  I then pour the starter into the milk and whisk it to combine.  The mixture will now be between 100 and 110 degrees, which is perfect.

To fill the jars, I pour the yogurt base from the pot into the 1-quart measuring cup and use the measuring cup to decant the base into the jars. 

INCUBATION:  I have a two-tier yogurt maker like this one.  When I make a full batch, the stuff on the bottom comes out thicker and tarter than the stuff on top:  there's just enough difference in temperature to change the result.  (See what I mean?  There are a lot of variables here, and small variations can make noticeable differences in some cases.)  My solution to this problem is to switch the jars halfway through the process.  It works fine.

So I set my yogurt in the machine and let it incubate for 4 - 6 hours (more about this in a second).  I switch the two layers halfway through the time.  When it's done, I cover the jars and refrigerate the yogurt overnight.

So why 4 - 6 hours?  Well, it depends.  In the summer in Arizona, we keep the house at 80 degrees F.  At that temperature, the yogurt takes 4 hours, with a switch at the 2-hour mark.  In the winter when it's cooler, and in Maine, where it's also cooler, it needs a total of 6 hours.

If I were making only 7 jars (one layer, in other words, without the second tier), I would probably do 3 hours in warm weather and 4 - 5 hours in cooler weather.  Remember that the stuff on the top doesn't get as hot, which is why you need more time overall if you're doing both tiers.


1.  Choose your milk.  I use 2% organic.
2.  Decide on a heating method--try different ones to see what you like best and what fits best into your way of working.
3.  Decide on an incubation method.  Electric yogurt makers with automatic shutoffs are the easiest.
4.  Try different incubation times until you get what you like.

If you want Greek-style yogurt, just line a sieve with several layers of cheesecloth.  Put the yogurt in the lined sieve--about twice as much as the final quantity you're looking for.  Set the sieve over a bowl and put the whole thing in the fridge.  It will be creamy in as little as 2 hours.  The longer you leave it, the firmer it will become.  After 8 hours or overnight, it will almost be like a soft cheese.  Save the whey that runs off:  it's good for baking.  Just use it in place of milk in muffins or in place of the milk or water in bread.

A word about flavoring:  I always make plain yogurt.  I'm worried about adding things that might make the yogis unhappy.  I am also glad to eat plain yogurt, straight from the jar, but a lot of people aren't.  If you prefer flavoring, I recommend adding honey and fruit or granola to the plain yogurt right before you eat it.  That way, nothing will kill off the helpful bacteria before they get inside you!  You can also sweeten with maple syrup, brown sugar, or even white sugar.  Wheat germ, ground flax, and other grains can make a nice addition.  Sometimes I throw a little cereal in there.  This is a little moment of creativity in an otherwise routine process--always a good thing!

I'd love for you to try this.  It's more complicated to write about than it is to do:  all it takes is a little patience and some recognition that you'll have to fool with it until it comes out the way you like it.  If you're like me, you'll enjoy that process!

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