Introduction
In our quest to achieve perfection from our kitchen here in Auckland, we can’t settle for a standard product from the supermarket. Instead, we make our own fresh yoghurt in-house. This gives us much better pH control and control over our yoghurt’s gel-forming properties.
The main advantage of making our yoghurt in-house is that we create a much better product, which in turn enhances the taste and experience of our icecream.
The science and history of yoghurt
Fermented dairy foods are a vital part of human diet in many regions of the world. They’ve been produced since the era of Sumerians and Babylonians of Mesopotamia, the Pharoes of Northeast Africa, and Indo-Aryans of the Indian subcontinent. In many cases, we believe that the original discovery was by accident, due to the high ambient temperatures in these regions which causes milk to ferment, generating a distinctive viscous consistency, smooth texture, and unmistakable flavor. In modern cultures, yoghurt is also often fortified with probiotic cultures.
There are a lot of fermented dairy products available, but yoghurt represents a large portion of the market. It’s mainly sold as a semi-solid fermented product made from heat-treated milk, using the activity of lactic acid fermenting bacteria; usually Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus.
The lactobacilli are among the most important components of microbial flora in both intestines. The ability of non-pathogenic intestinal microflora to associate with and bind to intestinal brush border tissue is thought to be an important process in preventing harmful pathogens from accessing the gastro-intestinal mucosa, giving your body extra protection against harmful bacteria that you may ingest. Recent studies also show that consumption of yoghurt significantly improves the transit time of gastric content, which can be helpful for constipation and related disorders.
Making yoghurt
At Giapo, our process is slightly different to the big commercial factories. Before we add the starter culture, we sterilize everything that will touch the milk, including the bowl where the milk is incubated and the hook mixer that is used to help stir the mix. This is a very important part of our yoghurt production, as it reduces the risk of potential contamination.
Once sterilized, we add milk and the starter cultures, and bring the mix up to 40°-45°C, the ideal temperature to incubate the lactic acid fermenting bacteria. Fermentation usually begins at 40°-45°C. Fermentation converts the lactose to lactic acid, which changes the pH of the milk, reducing it from 6.7 to 4.6.
Some of The chemistry and physics behind yoghurt making.
The changes in pH causes changes in the casein micelle structure, due to the solubilization of colloidal calcium phosphate (CCP). As casein approaches the isoelectric point (pH 4.6, the point at which casein precipitates), the negative charge is reduced, decreasing the electrostatic repulsion between charged groups.
In yoghurt formation, when the milk and culture beging incubating, the pH is in the range 6.7 – 6.0, and the net negative charge of the casein is slowly decreasing, causing decreasing electrostatic repulsion. Since only a small amount of CCP is solubilized at this point, there is no gel formation yet, but when the pH drops into the 6.0 – 5.0 range, the net negative charge of casein micelles greatly decreases, dramatically reducing the electrostatic repulsion and steric stability. The increasing rate of CCP solubilization also weakens the internal structure of the casein micelles and increases electrostatic repulsion between the exposed phosphoserine residues, encouraging the formation of a structural network at the solution’s margin.
As the pH of the yoghurt approaches the isoelectric point at pH 4.6, the casein’s net negative charge decreases to zero, which removes the electrostatic repulsion between the casein molecules. The acidification process causes the formation of a three dimensional network of casein chains, creating the natural gel-like structure that gives yoghurt the traditional, rich velvety texture. So influencing the change of the Chemistry of the milk will change the physical state of it and the milk will become yoghurt.
The finished product
We use a good thermometer and a professional pH meter to detect when the yoghurt has reached the desired pH. The yoghurt is then immediately blast-chilled, to prevent further acidification and spoilage. This provides us with the freshest, healthiest organic yoghurt to use as an ingredient in some of our icecream flavours.
No comments yet.