Researchers reveal new method to transform yogurt production and extend shelf life

A team of researchers has developed a method to reduce bacterial cultures in dairy production by up to 80%, which significantly cuts costs and helps prolong product shelf life.

The findings could help shape new developments in yogurt manufacturing. They could potentially be implemented easily and immediately as they do not require new technology, just an adjustment to the temperature control during dairy yogurt production.

Researchers at the DTU National Food Institute, Denmark, who are highly experienced in studying lactic acid bacteria, considered what might happen if bacteria were left to acidify without being allowed to grow. 

Fermentation technique

Usually, yogurt production involves adding a large amount of yogurt starter culture to milk. This is fermented at 42°C for four to six hours to achieve the desired consistency. The yogurt is then cooled. 

However, this traditional process can be challenging because of the high costs for starter culture and limited shelf life. Post-acidification, where the yogurt continues to acidify during storage, affecting quality and longevity, can also be a hindrance for yogurt makers as it can impact quality. 

Post-acidification can cause the product to spoil by becoming overly sour, bitter, and prone to phase separation.

The new method uses only 20% of the usual amount of starter culture. The milk is first fermented at 42°C, per standard procedure, then the temperature is raised to 51°C for a few hours. The 51°C step also acts almost as a mild pasteurization phase.

The bacteria cease to divide but continue to produce lactic acid at this higher temperature. 

From lab to market 

The method has been tested on a smaller scale in the DTU National Food Institute laboratory.

“We have been studying microorganisms that can prevent growth of spoilage and pathogenic microorganisms for years. Before that we discovered that heat can have both beneficial and detrimental effects on cheese cultures. The approach we present in the article is an outcome of things that we have been working on for more than 25 years,” associate professor Christian Solem, who has researched lactic acid bacteria for more than 25 years and is co-author of a new paper in Food Bioscience describing their findings, tells Food Ingredients First.

“In principle, dairies could adopt the method as early as tomorrow. We have not observed any drawbacks, apart from the process taking an hour or two longer — and you will have a more stable and sustainable product.”

“Knowledge transfer can be a slow process. For instance, it took more than 30 years before the starter culture industry started aerating certain lactic acid bacteria cultures, although the benefits of this was demonstrated in the 60s. The dairy industry is also quite conservative. I hope that at least a few dairies would like to explore the possibilities, as this would provide them with a competitive edge.” 

The research comes amid increasing growth in the dairy yogurt category. Estimations show that, on average, each person globally consumes nearly 12 kg of yogurt annually.

“It’s like putting the bacteria on a treadmill — they’re not going anywhere but still working. This allows us to control the acidification while avoiding undesirable post-acidification,” explains Prof. Solem. 

“We eliminate up to 99.9% of yeast cells and mold spores, which would otherwise significantly shorten the yogurt’s shelf life.”

The research comes amid increasing growth in the dairy yogurt category. Estimations show that, on average, each person globally consumes nearly 12 kg of yogurt annually.

Extended shelf life

The exact shelf life extension has not yet been determined, but it is expected to exceed the current three to four weeks. This could have significant implications for both long-distance transport and food waste reduction.

The findings could lead to substantial benefits for dairies, which currently use up to 0.18 g of starter culture per liter of milk. 

“We reduce the use of starter culture by a factor of five. That’s a substantial saving, and it matters in an industry where profit margins are tight,” adds Prof. Solem.

“Yogurt is typically produced in large batches, and each production run requires cleaning and reconfiguration. With longer shelf life, larger and perhaps even more continuous production becomes feasible.”

“We have shown that the content of yeast and fungi can be greatly reduced. Since these spoilage microorganisms grow slowly at low (storage) temperatures, it will take longer before they reach a critical level and cause spoilage. It is not difficult to imagine the effect of, for instance, reducing the content of a particular spoilage yeast by 99%. Dairies and researchers can look into the shelf life-prolonging effect in the future; perhaps we can as well, if we get funding to do so,” he concludes.