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I am getting a really thick yogurt with fresh whole milk + cultures. What I do is:

  1. get the milk (3,8% fat) boiling (95°C)
  2. keep heating the milk, lowering the temperature to 85/90°C for ten minutes
  3. Cool the milk down to 40°C
  4. Add cultures and mix properly
  5. Store the milk for 9Hrs in a recycled Easiyo thermos with hot water wrapped in a pile

Simply perfect

One day I have tried to add jam and sugar during step 2, however the yogurt didn't get thick at at all, although it had a perfect taste. Conclusion: adding flavors may conflict with bacteria development.

So the question is, from your experience, what flavors and how much sugar can be added to yogurt allowing a proper thick yogurt? I have personally added vanilla powder at step 2

Share your experience!

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What result are you looking for? I don't understand why you would need to add sugar before culturing, and not just stir it in afterward like everyone else does. Is there some specific property you are trying to create/avoid? –  Anthm Feb 14 at 16:42
    
Not really. It's just a matter of flavouring/sweetining.. Adding sugar before culturing, will taste rounder than adding it later on. I wonder how sugared yogurt (shop) gets cultured? Maybe they add sugar after culturing and blend? –  Riccardo Feb 15 at 0:19
    
Yes, that is how they do it. –  Anthm Feb 17 at 16:09
    
@Anthm, did you ever blend? Does it get very watery or once again in the fridge it will get thick again? –  Riccardo May 15 at 6:50

2 Answers 2

up vote 3 down vote accepted

Creating the right environment for bacterial fermentation

Yogurt is made using a few different bacteria which excel at digesting the lactose in milk at warm temperatures. Each of those factors (culture, temperature, composition of milk,) is important in creating an ideal environment for bacterial fermentation.

You would not try fermenting yogurt using yeast or a bacterial culture different from yogurt starter, and you wouldn't expect the yogurt to ferment if you held it your refrigerator instead of a warm thermos. The composition of the milk is equally important. If you change a major component of the milk, such as by adding sugar, some fermentation may happen but the result will not be what you expect.

"Live active culture" vs. actively culturing

There is a difference between bacteria that is "alive" or "active" and bacteria that is currently doing something.

Imagine dry baking yeast in a canister. The yeast is alive, but inert. It's not in an environment where it can do anything. Add moisture and carbohydrates for it to act on, and it goes nuts. Put that dough in the refrigerator, and it slows way down. Until you cook the yeast it doesn't "die" or "deactivate" it just has various states of activity depending on its environment.

The yogurt culture is alive when you add it to the milk, alive when you're done incubating it, alive when you add sugar, and alive when you eat it, But it can't turn milk into yogurt unless you give it a very precise environment -- the right culture, the right temperature, the right environment in the milk, including the right amount of sugar.

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Anthm, why adding the sugar, flavors and blending after the Yogurt is fully cultured will not kill cultures? –  Riccardo Feb 18 at 8:09
    
I updated my answer to better explain your question. –  Anthm Feb 18 at 23:37
    
Thanks a lot, I appreciate very much! Any way to get in contact with you? I have a few questions more! –  Riccardo Feb 19 at 17:02

I routinely add 8% sugar and 2% vanilla (by weight of the milk) and get thick yogurt. Some flavors are reported to interfere with the process but I have had no problems with vanilla.

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