Thursday, 8 August 2013

Making Yoghurt

I have been meaning to write down how I make yoghurt for ages, and now I've finally got around to it!  It's really quite easy, and saves us so much money!  Instead of paying $5 or $6 for a 1L tub of yoghurt, it now costs about $1.20 for the same amount because it's just the cost of the milk that goes into it :) 

My yoghurt!

I make a batch about once a month, which lasts us for the whole month.  I separate each batch into about 5 or 6 sterile jars, and only crack each one open as needed, so there is never any problem with contamination in the fridge.

The taste is pretty much exactly the same as the tub-set Greek yoghurt you can buy, but varies slightly from batch to batch depending on incubation temperature and how long I have incubated it for.  Sometimes it is lovely and creamy, more like sour cream, and other times it tastes exactly like store-bought Greek yoghurt.  It's always delicious though!

You can eat it straight, or add a bit of jam or sugar and vanilla for flavoured yoghurt, or even use it in recipes as a replacement for sour cream (I have topped baked potatoes with it - yummy!).  I've also used it half/half with milk as a replacement for buttermilk in recipes, and it has the same effect. 

When I first started making yoghurt, I used David Fankhauser's instructions, and over time my method has modified slightly.  He's a professor of Biology and Chemistry, so he must know what he's talking about when it comes to making food-safe bacterial cultures!! :)

Enough chatter, how do you make it?!  Here's my version!

  • stove top
  • large pot with a lid
  • medium pot
  • cooking thermometer that can measure at least 40-90 degrees C. 
  • whisk, spoon
  • enough jars to contain the volume of milk you use
  • one smaller jar to save some yoghurt for the next batch
  • tap water
  • kitchen sink or tub
  • cooler bags, esky, or other container to incubate.
  • 1.5L freshly bought and unopened milk
  • decent scoop (maybe 1/3 cup) of yoghurt
(For the yoghurt listed above, you can either just save some from the previous batch, which is what I do - see instructions below, or if starting from scratch, buy a plain yoghurt from the supermarket - just make sure it has live cultures in it.  I haven't bought yoghurt in at least 9 months now, because I just keep reusing the previous batch!)


Sterilise jars:
Place all the jars and lids in the large pot, making sure that you can still close the lid.  If not, do this in batches.  For maximum sterility you should probably do the spoon which you use to scoop out the yoghurt starter as well.  I don't usually bother.

Add about 2cm (3/4 inch) water in the bottom of the pot, and heat on the stove until it boils.  Boil with the lid shut for 10 minutes.  Turn off heat, and leave the lid shut.  When you are almost ready for them (I do this when the milk is cooling), remove jars from pot without touching the insides or the jars or lids - be careful as they are hot, and set aside.

Sterilising jars.

Make Yoghurt:
Pour your milk into the medium pot, and clip the thermometer to the edge of the pot so you can monitor it throughout heating.  Heat the milk slowly and stirring frequently with the whisk so it doesn't stick and burn, until it reaches 85 degrees C.

Milk in pot with thermometer and whisk.

Meanwhile, partly fill your kitchen sink with cold water, and if you like, add ice cubes or freezer blocks to make it even colder (I do this because our cold tap is warm for most of the year). 

When your milk reaches 85 degrees, take it off the heat, and sit the pot in the sink of cold water to cool it quickly.  Stir it occasionally while cooling.  When it gets to below 55 degrees C (this is very important so you don't overheat and kill the yoghurt starter!), remove from the cold water, and add your scoop of yoghurt.  Whisk this in thoroughly, make sure it is incorporated evenly.

Pour the milk mixture into your sterile jars, and seal the lids.  Work quickly so they don't cool down too much.  (I always have one jar smaller than the rest, and leave this jar unopened in the fridge until I make the next batch of yoghurt to make sure I have a clean uncontaminated starter for the next batch.) 

Place the sealed jars upright in a place where they will be incubated at a constant temperature.  wrapped in towels inside an esky would probably work, I use a cooler bag inside another cooler bag, and place it in the sun.  Place your thermometer inside with the jars, and check the temperature.  I like to maintain above 40 degrees C, although down to 37 or so should be fine - it might just take a little longer to set.  Seal up your incubator, and leave to sit undisturbed until it is set - I tend to leave it about 6 hours.

Jars inside two cooler bags with thermometer. 

After 6 hours, open up your esky - your yoghurt should be set solid in the jars!  If not, either it needs more time (in which case the milk will have a definite smell of yoghurt by now), or something went wrong with your starter culture.  My jars always end up with a thin layer of what appear to be solidified bubbles on top - this is just bubbles left over from the whisking step, so don't worry.

Take your jars of yoghurt, label with the date, and put in the fridge!  The yoghurt will be nice and white in colour, and will smell deliciously like store-bought Greek yoghurt.  Enjoy :)

Jars of yoghurt!  The jar on its side shows it is set.