Our Big Fat Greek Yogurt

Here at the lab, we've been making our own yogurt for a while and wanted to share what we've found to be the most efficient way to do it, which includes making a single big batch instead of a series of smaller cups.  The whole process itself is really easy, consisting of essentially two ingredients and 3-4 steps, but there are a few tricks we learned along the way that have helped us fine-tune the process.  We also recently tried making Greek yogurt, which worked well enough that we decided to get excited and blog about it.

We normally start by adding 7.5-8 cups milk to a glass bowl.  We've been using whole milk lately, but skim, 1% and 2% work fine, too.

Our first step is to scald the milk so our yogurt cultures don't have any competition, and so the milk proteins start to denature, which can give a thicker yogurt in the end.  The fastest way is in the microwave--we do 12 min first, then in 2 min intervals until the temp is 180 °F or a little higher, but lower than boiling (~212 °F).  It works to do this part on the stove, too, but it takes a lot longer.

Success!  Now we play the waiting game.  The milk has to be less than about 120 °F before adding the yogurt culture or the culture will not do as well, and might even die.  It usually takes 1.5-2 hrs to cool, so it's possible to get a lot done in the meantime.

As it's cooling down, a skin will probably form on the surface.  It's probably mostly protein that was denatured during the pasteurization.  Don't throw it out!  It makes a good snack (or Jake treat).

Although the good bacteria you will add in the next step will typically survive at temperatures less than 120 °F, they do better closer to 100 °F, so that's the temperature to which we let ours cool.  Make sure to clean the skin off the top one last time.

The next step is to add your yogurt starter culture!  There are a variety of bacteria that will do the job well, each with their own subtle flavors and growing preferences (maybe we should do a post on that!), but the main point is that some live good bacteria are required to get started turning the now-sterile milk into delicious creamy yogurt.  Some of the ones we've used are shown in the picture.  From left: a half-cup portion of the previous batch we stored in the freezer, a box of powdered special fancy culture that was a gift from Matt and Elise, and a bottle of powdered culture from the local Amish grocery store.  It will also work to use store-bought plain yogurt if the label says something to the effect of 'contains live cultures,' and has minimal additives (like corn starch and sweeteners).  For this batch, we're going to use the stuff we saved from last time.

This step isn't too hard to figure out: add the starter culture to the cooled milk and stir it up.  At this point, we've added so much good bacteria that they should be able to out-compete anything that might get in from the atmosphere over the next several hours.

Our oven doubles as our yogurt maker.  Unfortunately, even just the 'warm' setting is too hot (~170 °F), so we just turn it on for a minute or two until it's maybe 120 or 130 °F, then turn it off.  The nice part is that the oven holds heat pretty well, so it will still be a little warm several hours later.  Note that it's ok if the oven is a little warmer than optimal to begin with because it will take a long time for that temperature to get to the middle of the bowl (as in, it probably never will, as long as the oven is turned off)--at the same time, the oven is losing heat to its surroundings, so having the temperature a little warm to begin with actually keeps the yogurt culture near the optimum temperature for longer.  That's another advantage to making the yogurt in a big batch like this--a large bowl is more resistive to temperature changes than the little cups are, which makes the temperature easier to manage.  There are economies of scale even within a homestead!

Then we put the milk/culture mix in the oven and close the door!  In the past, we've used the light bulb to help keep the temperature up in the oven (when we've had a working light bulb in there), but then we don't preheat it as much to begin with (only to 100 - 110 °F).

While the door is closed, the bacteria do their thing and, seven or eight hours later (i.e. overnight), voila!  Yogurt!  Don't stare at the oven while this is happening.  A watched culture never gets thick!  On the other hand, 'watching yogurt thicken' could be added to the list of exciting ways to pass time, next to 'watching paint dry' and 'watching grass grow.'

If we disturb the the surface a little, the curd separates from the whey a bit.  This yogurt will be thinner than probably anything available in the store, but if we stir it up a lot (until it's homogeneous), it works fine for eating with granola, cookie bits, animal crackers, or whatever we're into at the time.

After stirring, don't forget to save out a half-cup or so to make the next batch!  We've made a batch this size work with as little as a tablespoon or two of starter culture (much less for the powdered cultures), but in our experience, a half cup or more is pretty fail-safe.

Now it's time to get this yogurt Greekified.  It seems that the only real difference between regular and Greek yogurt is that the latter has the whey strained off, which makes it much thicker.  So here we are, with our whey strainer (a piece of muslin cheesecloth in a bowl).

We poured in the yogurt and tied up the corners.  Then we had to figure out a way to suspend it above the bowl while keeping the yogurt cold.  (Now the good bacteria have stopped growing as fast, and we don't want bad bacteria to settle in.)  There are most definitely more elegant ways to accomplish that, but this is what we came up with in the moment.  Good thing for mostly empty fridges, wire racks, and muslin cheeseclothes that at first glance appear way too large.  We probably could have used a colander or sieve to support the cloth also.

There's our little whey droplets, doing their condensation impression on the filter!  Either that, or the yogurt has broken into a cold sweat thinking about the Greek economy.  (To be fair, yogurt from almost any nation could have similar concerns.  Except yogurt from Greenland, but it would probably be frozen by this point anyway.)

We've managed to drain quite a bit of whey!  The yogurt will surely be thicker now.

Definitely thicker!  Of course, our yield is lower, too, but look!  It's much thicker than before!

Don't waste any!  It's not too hard to scrape off the cloth with a spatula on a flat surface.

Also, don't forget to use the whey for something, like corning meat, baking bread, or making tea!  We made a big jar of chai tea with ours this time.  However, in the process of heating it up, leftover soluble protein or small curds that made it through the filter might denature, similar to what happens in making ricotta cheese. (ok, exactly what happens in making ricotta cheese).  So, it might be a good idea to make the ricotta, separate it from the remaining whey, and then make the chai.  That's what we'll do next time.

Have you made your own yogurt at home (Greek or not)?  Have you used other types of milk (goat, sheep, etc.)?  Tell us about it in the comments section below!