Curd can be tough to set for various reasons: the milk was too hot or too cold when the curd starter was added; the starter was weak or too little; the room temperature was not hot enough; or the milk was low in solids. Fix the temperature first; make sure the milk is lukewarm, around 37- 45 degrees Celsius, and you’ll see most of the problems disappear.
When you lift the lid and see a loose milky puddle instead of the thick creamy glossy curd, that instantly disappoints one’s mood. Setting curd looks effortless but requires discipline; our grandmothers could do it without a thermometer, but sometimes it sends us for a toss so bad that we look for answers on how to set it properly.
Well, the reassuring thing is that setting curd is not about luck but a small piece of science knowledge. Curd formation happens when lactic acid bacteria starter feeds on natural sugar in milk and then produces lactic acid. When milk starts turning acidic gently, it draws the protein together and traps the liquid, and now what was fluid once turns into a sliceable gel. When you get the conditions right, you will get thick curd every time.
This guide will help you understand the common mistakes because of which curd does not set and simple ways to fix it. Almost every failure leads to a cause; once you identify them, a good set curd stops being a gamble.
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Dahi is prepared by adding harmless lactic acid bacteria to the milk that has been pasteurized, which is popularly known as jaaman by many families. Those bacteria reproduce rapidly and turn the lactose present in milk into lactic acid. As acidity increases, the pH of milk drops to around 4.4-4.5; the casein protein loses its opposition toward each other and binds together, forming a net that holds the water and fats. This mesh is your curd.
There are two pitfalls we should watch for. Bacteria have to be alive and active, and they should have the right environment to work in. Almost every setting failure is really a failure of one of those two things, which is why the fixes below are so simple.
Lactic acid bacteria are living creatures which rely on their surroundings. If you add the starter to boiling milk, this heat will destroy the bacteria, and nothing will be fermented. If the temperature is too low, the bacteria will be inactive and the curds will either take a long time to form or not set at all.
To fix this problem, let the milk cool down a little before adding the starter; the ideal temperature for that is between 37 and 45 degrees Celsius, which is about the temperature of warm water. A simple trick here is to put your finger into the boiled milk to check the temperature; it should be warm and not too hot before adding the starter.
The curds that have been turned sour over time or have spent a lot of time in the fridge may not have enough active culture to work properly. If the amount of the starter is not enough, there is not a sufficient number of bacteria to turn the mixture sour on time.
The best way out is to use fresh and whole curds as starters, and when doing so, please remember that even a tablespoon may be enough for one bowl of milk. If your set has been getting weaker batch after batch, refresh the starter with a fresh, live curd, and the chain usually recovers.
Even the best culture will fail to do its job if the air temperature is low because the milk cools down before the fermentation process is over. This explains why curd works so well on a warm summer evening but never works in winter.
The solution: make sure that the pot remains warm. Put it in the oven (make sure that it is off), wrap it in something warm, or place it where there is heat in the kitchen. In winter, you can help warm the bowl before pouring the milk by rinsing it with hot water, which will help maintain temperature longer.
The protein network is delicate when formed. Any shaking, stirring, or moving of the pot at this stage can cause the gel to break down and never firm up. Therefore, the curd must be allowed to set undisturbed.
Fix: After mixing in the starter and covering the pot, simply put it in a warm place and leave it for several hours before unearthing your creation.
The firmness of curd depends a lot on solids-not-fat (SNF) in milk. Low solid content, diluted, or very low-fat milk results in weak reaching, although the process is done correctly. The higher the SNF content in milk, the firmer the body is.
How to overcome this issue: use milk that is high in quality and meets standards. Toned and double toned milk have solid SNF content; they reach the flocculent stage well. Boiling milk for a while before cooling is the practice some cooks employ.
Sometimes it is the milk itself that causes the problem. Antibiotic residue, for example, could be present in poorly produced raw milk and prevent fermentation. Thus, using milk from a trustworthy source is advisable.
How to fix this situation: turn to milk from a licensed producer such as Aashirvaad Dairy, which guarantees high-quality milk. If a batch of milk fails to curd repeatedly despite unchanged preparation methods, then the milk should be blamed.
Fermentation is not an instantaneous process. Depending on the temperature and the effectiveness of the starter, a proper set may take several hours; a cool night can make this process even longer in time. If you check too early and declare it a failure and stir it, you can make a curd that just needed more time into a curd that will never set.
The remedy here is patience. Give it sufficient undisturbed time in a warm place, and judge the set only once. If it is close but still soft, leaving it for a while longer will often do the trick.
Most times, the milk was either excessively heated or chilled when introducing the starter culture. While the lactic bacteria in the hot milk die, they also stop functioning in cold milk. Repeat the procedure making use of lukewarm milk (37-45°C), and the milk will probably coagulate.
Lukewarm milk should be about 37-45°C, just warm up to the touch, not hot. It is the perfect temperature that guarantees the multiplication of starter bacteria for a proper acidification process.
It is common for curd to be too liquid when the pan with it is disturbed while the milk coagulates, low-fat milk is used, or the fermentation process is shortened. Make sure to leave the curd undisturbed, use good quality milk, and give it enough time to set properly.
A teaspoon of starter culture per litre of milk is a common ratio. Quality matters more than quantity; too much starter may spoil the curd.
Cold temperatures prevent the milk from getting warm enough. Try to keep the pot in a warm place to avoid disturbance and provide ambient temperature.
Milk with a high solids-not-fat content gives a firmer set. Toned and double-toned milk are also successful, while whole milk yields a richer curd. Always use a reputable brand with high-quality milk.
Indeed. Poor-quality milk with low solids creates less solid curds, and bad-quality milk can reduce the ability of the culture to work. If everything remains the same and curds keep failing to form, consider the milk as the source of the problem.
It usually takes several hours for the curds to form, and the actual time depends on the temperature and characteristics of the starter. If everything is fine, don't disturb the curds too often to prevent them from forming properly.
Curd might have been left to ferment for too long. To make curd less sour, keep it in the fridge once it gets thick.
It is prudent to boil the milk beforehand to ensure safety and helps produce firmer curd. Just remember to cool it down till it's lukewarm before adding the starter.
To set a firm, thick curd, you don't need luck or a secret touch; it is a matter of providing the conditions the bacteria need to grow: a live starter, lukewarm milk, an undisturbed place which is fairly warm, and milk with enough solids. Missing either of the conditions makes the curd suffer; if you get it right, it will set beautifully every time.
Next time your curd fails, run down the list, check the temperature first, then look into the starter, stillness, and milk quality, and you'll most probably find your culprit, and so much comes back to milk: use a trusted source like Aashirvaad Dairy quietly stacks the odds in your favour before the starter even goes in.