A guide to fermented foods and yogurt

Reading Time: 6-8 minutes

Fermented foods

Fermentation is a natural process that microorganisms such as bacteria, yeasts and moulds use to obtain energy for growth and development. Fermented foods are defined as “foods made through desired microbial growth and enzymatic conversions of food components”.[1] In fermented foods, microorganisms known as ferments preserve and transform the food components into more stable and diverse foods with unique properties, for example turning milk into yogurt, or grape juice into wine.

The microorganisms found in yogurt, kefir, cheese and kimchi can still be active in the final product. However, some fermented foods undergo further processing after fermentation that kill or remove the live microorganisms, e.g. soya sauces, most beers, wine, bread (including sourdough), and chocolate.[2] Fermented foods are an important component of a gut-friendly diet, but the live cultures within them may not meet the specific definition of a ‘probiotic’. See the Fundamentals of the Gut Microbiome, Fermented Foods, and Biotics section for more information on probiotics and the specific definition.

Yogurt

Consumption of dairy products is believed to have started as far back as 10,000 BC with the domestication of milk-producing animals.[3] Yogurt, which is a fermented dairy product, now forms an integral part of the diet in many cultures globally.

Standard yogurt is made by fermenting milk with specific symbiotic starter cultures:

• Lactobacillus delbrueckii subsp. bulgaricus (left)

• Streptococcus thermophilus (right)

To be classified as yogurt, these starter microorganisms must remain viable, active, and abundant in the product until the minimum durability date.*

Additional microorganisms may be included for functional reasons, such as to support health, or for purposes of improving taste and texture.

Understanding the Different Types of Yogurt[4]

Today there are many different yogurt varieties on the market, which can differ based on their manufacturing processes, the type of milk used (skimmed, semi-skimmed or whole) and ingredients added before or after fermentation.

The chemical process during milk fermentation

Raw milk for yogurt production is pasteurised (heated to 176ºF or 80ºC) and homogenised before being cooled to 109.4-114.8ºF (43-46ºC) during which the fermentation cultures are added. During fermentation, Lactobacillus bulgaricus and Streptococcus thermophilus chemically transform the lactose naturally present in milk into glucose and galactose which are then converted into lactic acid.[6]

Lactic acid naturally preserves the yogurt and provides some acidity, which helps coagulate caseins (milk proteins), which ultimately gives yogurt its unique texture and flavour.[7]

Once the desired consistency is obtained, the yogurt is cooled to 40ºF or 5ºC to slow the growth of the bacteria and maintain its texture, flavour and acidity. After cooling, other ingredients may be added, like fruits, grains and flavourings.[4]

The viscosity and pH of yogurt changes during the fermentation process due to the activity of bacteria: viscosity increases as pH decreases.[8]

Activia’s unique fermentation – at 37°!

Danone’s founder, Isacc Carasso, created the company’s first yogurt in 1919, after recognising that many children in Spain suffered from gastrointestinal problems. He made the yogurt by mixing fresh milk with ferments which he packaged in porcelain pots and sold as a health food in pharmacies. To learn more about our history in yogurt click here.

Danone’s Activia yogurt is a unique fermented dairy product made of a mix of five exclusive strains of bacteria that each play a specific role in the fermentation process. Visit our page on the importance of strain specificity to learn more about the specific strains in Activia and their roles. Fermentation occurs at a lower temperature in Activia, 37°C vs 43-46ºC, and in a less acidic environment than other yogurts, allowing the live bacteria – in particular Activia’s B.lactis CNCM I-2494 strain to thrive and produce a milder tasting, more alkaline yogurt.

It is important that the microorganisms added to milk have the best possible growth conditions. If the fermentation time is not properly managed, it can lead to a yogurt with a completely different flavour, consistency and outcomes.

*As described by the United Nations’ Food and Agriculture Organisation and the World Health Organisation in their Codex.[4]

Explore more

• Activia science

• Blogs

• Our expert authors