Fat-free stirred yogurts: How to get the right recipe?
Agriculture and Agri-Food Canada
From our first spoonful of trying a new yogurt, we immediately decide whether we like it, whether we will buy it again, and even whether we will suggest it to our friends or put it in our kids' lunches. But what do we base our decision on during these first few moments?
It is important for food processors to understand what consumers prefer and consistently reproduce these qualities from batch to batch. Stirred yogurts present special challenges because there are many stages to go through - from the initial fermentation to the final product. Fat-free yogurts are even trickier to produce, as fat provides some structural stability to the yogurt, and in its absence the milk protein has to do all the work.
Sébastien Villeneuve and Daniel Saint-Gelais, from the Agriculture and Agri-Food Canada Research and Development Centre in Saint-Hyacinthe, and Valérie Guénard-Lampron, Ph.D. student, looked into the subject. A good yogurt has the right viscosity (not too runny nor solid), is uniform (no lumps) and does not lose its whey, that is to say that the liquid does not separate to the surface and change the texture.
"The main advantage we had in making our results more realistic for an industrial yogurt producer's reality is that the facilities in the Saint-Hyacinthe [Research and Development Centre] allow us to work with large quantities [of product]. So, our results are more easily transferable to the industry."
- Sébastien Villeneuve, Research Scientist, Food Process Engineering, Agriculture and Agri-Food Canada
Early in their research, the team found that, as proteins do all the work of creating texture in fat-free yogurts, the temperature of the different stages is crucial. This is because proteins are very sensitive to temperature variations, similar to how egg whites are sensitive to heat in a frying pan or gelatin is sensitive to cold in a refrigerator.
Stirred yogurt must be fermented in tanks, cooled, transported between tanks, stirred, smoothed and then packaged in its final container. Each step in the production line has the potential to affect the quality of the yogurt. To find out the best order and conditions for each step, the team conducted many tests. They cooled the yogurts before or after stirring, in various types of machines with different levels of pressure, and varied the duration of each stage. They also studied how yogurt behaved its final container over 22 days to see if the whey separated from the yogurt and if the texture was stable over time.
To fully understand the effects of each variation in the process, the researchers even turned their attention to what is happening at the molecular level, such as how proteins bind together at each step.
Depending on the desired type of yogurt, the recommended process varies; however, some of the team's findings always hold true. For example, if the yogurt is too cold during the stirring and transportation phase, its structure completely breaks down and it cannot regain the right texture essentially it remains too runny. If it is too hot, it will release its whey as it cools.
In concrete terms, the results of the studies by Villeneuve, Saint-Gelais and Guénard-Lampron will help yogurt producers make decisions when constructing their industrial production lines. There are always compromises to be made, but thanks to the Saint-Hyacinthe team, producers know more about how and why their decisions impact their yogurts.
Key discoveries (benefits)
- A team from Agriculture and Agri-Food Canada's Saint-Hyacinthe Research and Development Centre deepened our knowledge on the manufacturing of stirred yogurts, particularly fat-free yogurts.
- The team found that protein does all of the work of creating texture in fat-free yogurts and that the temperature of the various production stages is critical. Depending on the type of yogurt desired, recommendations vary.
- In general, if the yogurt is too cold during the stirring and transportation phase, its structure completely breaks down. If it is too hot, its whey will separate as it cools which will change the texture
- The results of this study will help yogurt producers make decisions when constructing their industrial production lines.
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