[Womble]

When I was an impoverished student, I made yoghurt by mixing some shop-bought yoghurt with evaporated milk and the same amount again of boiling water, then stuck it in the airing cupboard overnight. It never failed!

However, I've tried again sporadically over the past few years, using an easiyo maker, my Mum's old electric one, and latterly an instantpot, but nothing seems to be reliable!

I've so far made curdly mess, accidental cottage cheese, rancid milk and various other failures alongside rare successes, but I just can't seem to get it consistent any more.

HELP!!! 

[SallyintNorth]

Use regular milk, unhomogenised if you can get it.  Heat it to the temperature you need. 

Use freshly-opened ingredients (both milk and yoghurt) and sterilised containers and utensils. 

If you get spoilage again, try re-pasteurising the milk by heating it to a temperature where a skin starts to form, hold it there for at least 30 seconds, cool to around 40-45 degrees (check using a sterilised thermometer, not your finger!!), then stir in the yoghurt. Be mindful of possible contamination at every step.

If you're still having problems, try a different seed yoghurt.  I find that plain Arla Skyr works very well.  Yeo Valley works okay although the result can sometimes be slightly slimy. 

[SallyintNorth]

It's not as difficult to make and use your own culture as you think.  And it's a lot nicer, and a lot cheaper overall.

You can buy sachets of freeze-dried culture, each sachet makes a litre of starter.   (Or if you are super-thrifty, you can probably get up to 4 batches of starter from one sachet.)  I freeze the starter in ice cube freezer bags (although some products say do not freeze the resultant starter.)  I find that with good hygiene, I can get 3 or sometimes 4 generations from each dollop of starter before it starts to deteriorate, so I take another set of ice cube starters from each of the 2nd Gen batches I make.  And if the resultant 3rd Gen is coming out perfect, I might save some of that for a 4th gen.

I can't even do the maths, but it must be *hundreds* of litres from the original sachet, which cost less than a fiver. 

I used to buy mine from Ascot Smallholding Supplies and then Goat Nutrition, but Ascot is gone now and GN no longer sell cultures.  There are suppliers (eg linky) but I can't give a recommendation as I haven't bought from any of them. 

[Womble]

Thanks Sally,

I've now had one successful batch from a Yeo Valley plain yoghurt starter and whole milk, which I then used to start another, which also worked.

I haven't done anything different except to change the starter, so perhaps that was the problem?

I did buy some powdered starter at one point which was ok, but not brilliant. The packet said you must not re-use the starter upon pain of death..... but of course they would say that, wouldn't they?

So how much yoghurt starter do you use per litre of milk then, and do you think that ratio is important?

[SallyintNorth]

I don't think the *ratio* is important, no, but there needs to be enough starter to colonise the milk quickly enough to ensure they're the dominant bacteria. 

Being able to maintain temperature helps; the bacteria become more sluggish as the temperature drops.  So as well as maintaining the temperature of the vat, if the starter is refrigerated, let the dollop you're using be at room temperature at least before adding it to the milk which is already at blood temperature, so that the bacteria are raring to go and start reproducing immediately.

Having no contamination helps, so re-pasteurising the milk and being super careful with containers and utensils can make a big difference.  If I was being stingy with the starter I would almost certainly (re)pasteurise the milk and try to keep the temperature close to blood heat as long as possible, at least for a few hours.

I mostly make much bigger batches.  I used to use a jamjarful of starter to a gallonish of milk.   If I was just doing a litre I'd probably use a "good dollop", roughly tablespoon of starter maybe.

[Womble]

Thanks Sally,

The instantpot (electric pressure cooker) has a setting that automatically boils the milk to re-sterilise, then I let that cool to about 45 degC, add the starter and set it to maintain that temperature overnight.

That seems to be working (now, with the Yeo Valley starter), so I'll keep doing that and see if I can achieve consistent results.

[SallyintNorth]

Glad you're now getting yoghurt you like.

Boiling the milk will indeed sterilise it, which is not the same as pasteurising.  Boiling denatures the proteins, and the resultant curd will differ to one made with pasteurised, unboiled milk.  Which matters not one jot if you like what you are making!  But I just thought it worth mentioning for anyone else reading this thread anytime.