Instant pot yoghurt

Based on the previous post that compared yoghurt recipes, this recipe was more a trial run of IP and a science test rather than any attempt to make a refined product. At the end of the recipe, I'll input some learnings to improve the recipe for next time. I'm using deg F for this recipe instead of C purely because I don't have a digital thermometer and my analogue one reads in 5 deg F increments.

Ingredients

2l of milk (slighly over the half gallon that 1 recipe suggested)

¼ cup of yoghurt as a starter

Method

1) Press the Yoghurt and Adjust to boil the milk. It should come up to 180 deg F (optimum 82 to 87 deg C).

2) When it beeps, stir/whisk with a plastic whisk and check the temp. You may need to reboil. I tried two further cycles but finally needed to use the Saute function to get it over 180 deg F. This took about 30 to 40 mins.

3) Take out the inner pot and put it on a wire rack (or water bath) to cool. Bring the temp down to 110 deg F (optimum: 42 to 45 deg C; about 40 mins on a 29 deg C day). Remove the skin that has formed on the surface.

4) Temper the starter by putting it in the container that will be used to hold the yoghurt. Add ½ cup of the milk mixture and whisk. Pour it back into the main pot and whisk to incorporate

5) Put it back in the IP and press Yoghurt and set the time for 8 hours. I was worried that my 8 hrs would end over night which might spoil the yoghurt but it went to the yoghurt keep warm and it was all right.

6) Whisk smooth so the fat globules disperse. Pour into the prepared containers. Ideally, these should be sterilised so that the yoghurt will last longer but I didn't bother.

Recipe feedback

1) Some recipes recommend sterilising the pot and equipment and I was a bit paranoid whether my equipment (my thermometer, scoops, whisk, yoghurt containers, etc) would introduce bacteria that would affect the final product but they didn't. However I did sterilise the pot beforehand and let it air. The IP has to cool down thoroughly or else the milk might scorch at the bottom. The thermometer, scoop and whisk were 'sterilised' when they was immersed in the liquid, and I didn't wash it until I left it to incubate, so that seemed ok.

2) The recipes recommend removing the skin and whisking the final product before pouring the yoghurt into the empty containers but I didn't. The product turned out lumpy and I could taste the skin. Not really noticeable but something to note for next time.

3) The yoghurt was slightly thinner than the store bought pot set yoghurt but I didn't really mind. I could strain it a bit as some recipes suggest but again, it didn't really bother me. 

4) Trying to 'hold the boil' at 180 deg F for 5 mins proved difficult using the saute function (high) as the temp kept climbing. I ended up bringing it to 190 deg F (and was afraid that I had killed off some bacteria or something) and then letting the temp drop naturally, so it stayed at 180 deg F for about 5 to 7 minutes. Not a bad 'accidental' find with no adverse effect on the final product.

5) I didn't add sugar or vanilla but these can be added at the same time as the starter.

6) Some recipes suggest that adding less starter (i.e. 1 tbsp for ½ gallon instead of 4 tbsp or ¼ cup) and incubating for longer (ie 10 hr) would lead to a less sour product. I found it less sour than store bought and relatively thick despite using 4 tbsp of yoghurt and technically incubating for 20 hours, so I'm not convinced about this point.