I like yogurt, but I never asked myself how it was made. I saw the label “with live cultures” on the yogurt container all the time. Until last Saturday when I sat down to consume a 6-oz 8% fat yogurt did I notice “with active acidophilus and bifidus cultures” on the outside. The biologist side got of me and I read the ingredients carefully and learned that it contained S. thermophilus, L. acidophilus, Lactobacillus bulgaricus, and bifidus.
In the Food Section of today’s New York Times there is an article about the sequencing of the Lactobacillus bulgaricus genome and how the bacterium had evolved to adapt to living in milk to make yogurt. This organism now only digests lactose, the main sugar in milk, and has lost its ability to metabolize other sugars. That is amazing, giving that people only discovered how to make yogurt about 5000 years ago in the Balkans and the Middle East. Yogurt is made when the above-mentioned stains of bacteria break down lactose to lactic acid that acidifies the milk and makes it to clot. This acidified environment also prevents other strains of bacteria from growing. The yogurt culture further breaks down lactic acid to glucose and galactose, giving yogurt its sweet taste.
So if you want to try to make yogurt at home, here is a recipe (borrowed from here):
1. Heat 1 liter of milk to 85 ºC and maintain at that temperature for 2 minutes. This step kills undesirable contaminant microorganisms. It also denaturizes inhibitory enzymes that retard the subsequent yogurt fermentation.
2. Cool milk in a cold water bath to 42-44 ºC. The cooling process should take about 15 minutes.
3. Add a few teaspoonfuls of the store-bought yogurt as the starter culture. Mix.
4. Cover the container to minimize the possibility of contamination. Incubate at 42ºC (in an oven) for 3 to 6 hours undisturbed until the desired custard consistency is reached. Yogurt is set when the mixture stops flowing as the container is tipped slowly.
5. Chill it and enjoy your fresh yogurt!
Guess how the 8% fat yogurt bought from Whole Foods tastes?
1 comment:
自沙一下啊。
8% fat yogurt tastes really yummy. Usually I only eat fat-free yogurt and it tastes good. But 8% fat is like heaven compared to fat-free. The only thing that will stop me from going to Whole Foods for it all the time is that it is kind of expensive. That helps for my health and well-being, too.
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