Yoghurt making : effects of temperature and duration [duplicate]

As I am fairly new to making yoghurt at home I would like to understand the effects that temperatures and time have on the end product in both the initial heating/cooling step and the fermentation step.

So far I have made half a dozen 1.5 litre batches with three different cultures (currently using ABY-1 from CHR Hansen that I was able to buy from the Westcombe dairy in Somerset). I have a Luvelle machine that can ferment at 36C, 38C and 40C from 1 hour to 24 hours.

I want to understand what changes if I experiment with the following:-

When I heat the milk to 85C and hold the temperature I have made some batches with a 10 minute hold and others with a 20 minute hold period and see/feel/taste no difference - will holding at 30 minutes produce a difference?
I am currently fermenting for 24 hours at 38C and getting a strong tang/sourness to the yoghurt but what would I expect to get if I reduced the fermentation to 12 hours at 38C...or less?
I choose 38C for the fermentation process because it was recommended by the manual that came with the Luvelle machine but what happens if I use 36C or 40C and what length of time would I use?

So generally speaking I want to know more about the initial heating process and what options there are and what the different fermentation temperatures and durations can have on the end results.

Thanks in advance!

Best Answer

First, about the holding time: It is a safety feature. It is meant to ensure that the number of non-culturing organisms that survive is so low that the culturing organisms can overtake them and create a colony of their own, without pathogens. If you reduce it, sometimes nothing will happen, and sometimes you will get a dangerously high growth of pathogenic bacteria. To keep your yogurt safe, you have to do the 30 minutes.

Second, fermentation time and temperature. When you stay close to the prescribed temperature for a given culture, then you can trust that a higher temperature will give you the same sourness in shorter time, or more sourness in the same time. If you go far away from the prescribed temperature, your fermentation process again becomes unsafe (because some other bacteria are likely to take over before your culture multiplies enough to establish itself). From experience, a deviation of 2C from the optimal is close enough to still make good yogurt, so you can experiment with all three temperatures. What happens if you use 36 C is that you get less tangy yogurt, and at 40 you get more tangy. The length of time you use is pretty much a matter of trial and error, until you get the taste you prefer.

Note that, for establishing your preferred time, you should use an established culture. That is, you should either always use a new capsule of lab-bought culture, or you should first do a few generations of reinnoculation at constant conditions, and then start experimenting from there. This is because the first few re-innoculations from a new capsule are a kind of "adjusting" fermentations, and your yogurt will be changing its tanginess and consistency even when you keep the conditions (time and temperature) equal.

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How does temperature affect yogurt making?

The temperature must be 108\xb0F to 112\xb0F for yogurt bacteria to grow properly. Too high a temperature inactivates bacteria; too low a temperature prohibits growth. Inhibitor substances such as detergent from dishes. Wash and rinse dishes well before making yogurt.

How does time affect the yogurt?

The viscosity of yoghurt is affected by fermentation time. The longer fermentation time would produce thicker yoghurt viscosity. The addition of stabilizer would increase total solids content, water holding capacity, and thicker yoghurt.

What is the significance of temperature on fermentation during the production yogurt?

As the incubation temperature is increased the viscosity of the yoghurt increases, the brix (percentage sugar) reduces, the pH reduces and titerable acidity increases. This results in a thicker gel more firmness and adhesiveness as incubation temperature is increased.

What will happen to the yogurt if you keep it to ferment for a longer time?

Then transfer cultured milk to preheated jars, seal, and place in the incubation chamber, leaving it to ferment undisturbed. Incubated at 115\xb0F/46\xb0C, yogurt will coagulate within about three hours, but if left too long it can easily curdle.

Making Yoghurt | Health | Biology | FuseSchool

More answers regarding yoghurt making : effects of temperature and duration [duplicate]

Answer 2

Not sure if I should edit the question or add a new answer (comment space was to short for this). I was able to find an interesting website (https://dairyprocessinghandbook.com/chapter/fermented-milk-products) that covers all aspects of yoghurt production and I found this section....

HEAT TREATMENT The milk is heat treated before being inoculated with the starter in order to:

Improve the properties of the milk as a substrate for the bacteria culture
Ensure that the coagulum of the finished yoghurt will be firm
Reduce the risk of whey separation in the end product

Optimum results are achieved by heat treatment at 90 – 95 °C and a holding time of about five minutes. That temperature/time combination denatures about 70 – 80 % of the whey proteins (99 % of the ?-lactoglobulin). In particular, the ?-lactoglobulin, which is the principal whey protein, interacts with the ?-casein, thereby helping to give the yoghurt a stable body. UHT treatment and sterilization of milk intended for culturing do not, however, have the same favourable influence on viscosity, for reasons not yet fully understood.

So rather than heat to 85C and hold for 30 mins maybe I should try heating to 95C and hold for just 5 minutes? Anyone tried this?

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