I second these questions. I use the Greek yogourt from a local dairy shop as starter and the results are amazing, but I have never been able to use my yogourt as starter for the next batch, no matter how fresh it is.
You might like to try kefir grains. They are very stable, I've had the same grains for 5+ years, and you can leave in the fridge for months if you like.
I used to use dedicated yogurt culture, but "kefir yogurt" tastes exactly the same to me, so I use it for everything (yogurt, goat cheese, kefir-the-drink, obviously).
Thank you for the recipe. I don't think I'll ever make it that way though. Stirring the milk non-stop until it reaches 185°F and then continuing to stir if for another hour is much more work than I'm willing to put in.
Milk kefir usually doesn't require any temperature control, it just goes faster when the ambient temp is higher. I believe the idea is that the kefir 'team' is able to easily outcompete any weed microorganisms. For me it's as simple as: Strain in plastic colander, rinse jar, put grains and fresh milk in jar, then place in cupboard. If I want to delay then it can be placed in the fridge instead for months/years and still be able to be revived later.
Apologies, should have read the link.. which is indeed about following a yoghurt-like process using milk kefir grains! But you don't have to do it that way, it can be really easy!
Just to clarify, I have been able to use one batch to start the next. I've used various yogurts from Whole Foods (2% or whole, but always plain/unflavored).
My first culture lasted through about 15 cycles (8 mo) before developing a weird blue cheese odor/flavor. When I started again, I also noticed the first batch of the new yogurt was substantially thicker than the last batch of the old yogurt.
The trick I've used is that I freeze cubes of the first batch in an ice-cube tray. Then whenever I make more, I unfreeze a cube, so I'm always making a "second generation" batch. My first generation I make from packets you can find online for ~$1.
I used to scald milk (in an Instant Pot this is the yogurt "high" setting) before making yogurt, but no longer do so.
Now I buy UHT pasteurized milk, which encompasses most organic milk, and simply run 18 hours of the Instant Pot "medium" setting. I start the instant pot, add two half gallons of milk, then pour in some Bulgarian yogurt as a starter and stir, then lid on and leave it alone until it beeps at me.
I normally get around three gallons of yogurt out of a one quart jar of the Bulgarian, which comes in a conveniently Mason-threaded quart jar, where I hoard the leftovers for storing my own yogurt.
Why did you switch from scalding regular milk to UHT? 18 hours is a long time to make yogurt. I do the scalding, let it cool in a fridge for an hour, and then make yogurt for 6.5 hours. This works for non-UHT milk (doesn't for UHT).
I just use the functions on my Instant Pot. The "Boil" function brings it to around 180°F. Then I let it cool to between 90-115°F before adding the yogurt. Then use the "More" function and it sets a timer for 12 hours ("Less" goes for 24, and I've never used it). All of these functions are available under the yogurt button on the Instant Pot.
My understanding is it may be possible to skip the boiling if you are using ultrapasteurized milk (lactose-free milk often is) from a just-opened container.
If you know any Indian family ask them. Most Indian households make yogurt every day and the culture is months even years old. They will use latest generation to make the next batch.
Get the biggest thermos flask you have. Get as much milk as it fits.
Get any yogurt. So far literally anything has worked: flavored, with added sugar or even the cheap versions with lots of gelatin.
Heat the milk around until it boils. Add sugar until it's slightly sweet but not too much (this will feed the culture. It won't be sweet after). Let it chill until 40c or slightly above body temperature.
Now mix in the yogurt, you need like 6 teaspoons for a liter milk, but just pour the container you have for good measure.
Pour the mix in the thermos flask and leave for aprox 4 hours, or until the whey separates. After that, the longer you wait the more acidic the yogurt gets.
Now time to strain. I put a sheet of coffee filter paper on the bottom of a pasta colander and another container beneath to collect the liquid. Pour the yogurt there, leave overnight in the fridge and you get thick Greek yogurt.
> Any one dollar plain yogurt from the supermarket works fine
A surprising number use additives to thicken them, and as I result I found I got better results from ones labeled Greek or acidophilus. I have no idea if there is any science behind this claim, so YMMV.
I've had a lot of success with plain Kirkland greek yogurt but most should work.
I also do 1 gallon at a time and microwave it to get it up to temperature. This takes about 20min from fridge to desired temperature.
After fermenting in my instant pot, I pour it into a fine mesh strainer on top of a large food container and put it in the fridge. The container is for the whey to collect in. This turns it into Greek yogurt.
I got a powder culture from Amazon because I am using raw milk and it would just not work with yogurt from the store. There are several different cultures available in 10 or 12 sachets and you might need a new one every 6 months or so. I tried a few different ones and I cannot feel the difference between them.
I've used Tillamook and brown cow as starters and they've been fine for a second batch at least.
I don't strain mine, instead i chuck in like half a cup/gallon of dry milk. It's sort of the bass ackwards method. Then I part it up into quart Tupperware.
I make 1/2 gallon at a time and strain with a cheesecloth for a couple hours. The output fits into a large round pyrex container.