Have you ever experience the thrill tinged with the sense of nostalgia when you rediscover something long forgotten? Yes, of course, I am talking about food here.
I had given up on making yogurt at home after a few failed or less than perfect attempts. Maybe I had gotten lazy and stopped exploring what could have gone wrong. Homemade yogurt also known as curd or dahi is something of a necessity in daily meals. It was something I used to do effortlessly in India with perfect results. Of course, I had always taken the hot weather for granted and never given it much thought. It was a simple affair of mixing warm milk with a teaspoon of culture and forgetting about it for next couple of hours. And voila, you had homemade yogurt! 5 months ago I moved to this cold country which I now call home. You can imagine my plight when I tried to use the same methods I used to use, and failing miserably. Finally, one fine morning, I decided to get behind the science of it all. Then, yesterday, I made a breakthrough!
Turns out I was doing a couple of things wrong.
1) The Milk: Never use lactose free or fat free milk. The bacteria in the culture need lactose to digest for their food. Without lactose, they will not grow and simply die. Fat free milk takes much longer to set, and may still have a watery consistency. Bottom line, use 1%, 2% or whole milk.
2) The Heat: I didn't boil the milk like I used to in India. In India, despite the milk being pasteurized, it is a common practice to first boil it and then use it. Because of the excessive heat, even a low bacteria count increases the chances of milk spoilage. As it turns out, boiling is an important factor in making yogurt. The heat changes or renatures the protein casein in the milk, which forms the bulk of the protein content in milk. According to some sources, the high heat also denatures whey, the other protein type present in milk. This allows formation of a more stable gel. Another function of heat is to reduce or eliminate other bacteria that may be present in milk so that the bacteria in the starter culture can flourish.
3) The amount and quality of culture: Used too little of it. One teaspoon is too less in a cold climate. Look for yogurt cultures with Streptococcus thermococcus and Lactobacillus bulgaricus in it. The bacteria break down the lactose to lactic acid which lowers the pH of the milk. This causes the clotting or soft gel formation of the milk. Ideally, these should be the only two bacteria present since they help in formation of yogurt. In probiotic yogurts, other bacteria are added, which means that the others will compete with these two for growth during time of incubation. This will result in longer time for formation of yogurt.
4) Not homogenizing the culture and milk.
5) Sustained heat at least 108F (42 degree Celcius). This step is necessary to allow a robust growth of the bacteria in the starter culture. The temperature should be sustained till pH 4.5 is reached. Because of cold and low activity of bacteria in the store bought cultures, longer period of heat is needed to allow ample production of lactic acid to reduce the pH of the milk.
I read countless articles about yogurt and yet none of them really gave me the perfect results I was hoping to get. Yogurt maker was completely out of the question. I avoid uni-taskers like the plague. I like my yogurt thick, but not dense like the store bought variety. Most recipes without the yogurt maker recommended using the oven. Maybe I have a rather large oven, or maybe its too cold out here, the oven never really worked. It became cold before the yogurt set too soon. And I was not very keen on keeping it on for the duration of 4-5 hours. What a waste of electricity! Then it struck me, a hot water bath should do the trick. I tried, and voila, after 4-5 hours I had my perfect dahi. The results almost made me weep with joy. So, without further ado, I present to you the perfect yogurt recipe.
Perfect Homemade Yogurt
Inspired by Science!
I used 2% milk for the recipe. I also used culture from plain, unflavored, store bought yogurt from an Indian store. Look for any brand with active or live bacteria mentioned above. The consistency of the yogurt improves with each successive batches of yogurt, as it becomes purer. The store bought yogurt culture may contain stabilizers which affect the consistency of yogurt.
2 cups milk (2%)
Culture (3 tablespoons)
Bring the milk on the stove in a pan to a boil. Remove from heat as soon as milk shows signs of reaching a boiling stage. Don't over boil as sustained heat will denature the proteins and will prevent formation of a thick curd. Transfer to a container with a tight fitting lid and let it cool to 98-112 F. In India, we traditionally use a steel container called lota to make yogurt. It will take a while for it to reach that stage, so don't wait around.
If the culture is thick, mix it gently with a whisk in a bowl. Once the milk cools to 112F, add the culture and mix it gently with a whisk to distribute the culture. Close the container with a tight fitting lid.
Fill a large vessel with enough water to submerge 3/4th of the yogurt container in water. The container should be large enough so that it can easily accommodate the yogurt container. Make note that the yogurt will displace some water, so use water accordingly. We don't want the yogurt container to submerge completely. Bring the water to just boiling. Remove from heat.
Place the container with milk and culture inside the hot water gently, making sure no spillage occurs. Now place this entire assembly in a closed environment such as an oven, microwave or a small cabinet. The yogurt should set in 4-5 hours. Place it in refrigerator for at least an hour before serving.