Making yoghurt by yourself may have various drivers. Sometimes it is difficult to obtain yoghurt without sugar, artificial flavors or colorants added. Sometimes it costs a multiple of the price of milk. But mostly making yoghurt is an opportunity to make a soft and full tasting product without additives. Making yoghurt is very easy and does not take much time. Many households on the Indian sub-continent do it daily.
The art of making yoghurt
Required is to have a small amount (50 g) of seed yoghurt available. This could be even sugar containing or flavored. Key is keeping the milk between 85-90 C for 25 minutes. Further, the temperature of the milk when the yoghurt starter is added is important. Higher temperature causes the product usually to be slightly more acidic. Finally, higher fermentation temperature causes the process to go faster. But the thicker gel that is formed may loose (or leak) water more easily than fermentation at lower temperature. In general we add the starter at 45C and then ferment at 40-45 C. The formed yoghurt will be thick after 3 hrs. Fermentation at 30 C may take 18 h.
- thermometer, range up to 100 C
- blanket or insulated box
Yoghurt, simple and delicious
Ingredients to make yoghurt
- 2.1 quarts (2 liter) milk full fat, reduce fat, skimmed, fresh, UHT treated or pasteurized
- 3 tbsp (45 g) seed yoghurt any commercial yoghurt or a left over from a previous batch
Instructions to make the yoghurt
- Place the milk in a pan with lid and heat at medium heat while stirring occasionally until the temperature reaches just over 85 C.
- Then stop heating, place the lid on and check every 5 minutes the temperature. Add heat when temperature drops below 85C and do not exceed 90 C. Do this for 25 minutes.
- After 25 minutes, place the pan in cold water to cool down. Occasionally stir the contents and the water bath. When the temperature of the milk has dropped to 47 C, take the pan out of the cool water bath.
- Then add the seed yoghurt and mix carefully.
- Place the pan now in an thermal insulated environment. One can use an insulated box, or wrap a blanket around the pan. The goal is to keep the temperature as much as possible elevated above 40 C. At the very least keep the temperature above 30 C (but the process takes longer).
- After 5 h above 40 C or 18 h at 30 C the yoghurt has set and is ready. Now place it in the refrigerator to further stiffen up and to store. Yoghurt can be stored for 2 weeks in the refrigerator.
- The reason why the milk must reach 85-90 C (but not lower and not higher), is that the protein lactoglobuline denatures at those temperatures. These proteins will then adsorb on caseine particles. The casein particles are conglomerates of each thousands of milk protein molecules, which then form gradually a fine network that is able to bind the liquids. This gives the viscous, rather gel like appearance of yoghurt.
- You can also make yoghurt from reduced fat milk. Possibly an even tighter network may be formed. As many milk producers add milk proteins to compensate for the reduced body of the fat reduced milk.
- The production is a biosynthetic process. Two strains of bacteria, one Lactobacillus and one Streptococcus strain are growing symbiotically. At the acid level of 0.5% and beyond, more of the Lactobacilli remain active and increase the acidity. The acidity comes from lactic acid, formed by anaerobic fermentation of lactose. There is also some acetaldehyde formed, which gives green apples their specific refreshing taste.
- In a cold kitchen, it may be more challenging to keep the temperature. In case the fermentation gets stuck because of low temperature, briefly microwave the seeded milk/yoghurt mixture. And then let nature proceed its course.
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