What causes curding in this case: heating milk with large quantities of sugar
Yesterday I decided to try to make dulce de leche or caramel. I did not follow a recipe: I was as curious to see what would happen as I was hungry for sweet, caramelised, milky sugar.
I mixed semi-skimmed milk with a large quantity of white sugar in a saucepan and heated gently. The ratio was roughly 1:1 by volume.
Within minutes (and long before the mixture was at all hot) smooth, silky shapes began to form in the mixture, which at this point was still roughly half milk and half undissolved sugar.
The silky shapes soon coagulated and grew harder and chewier over time. The milk had obviously curdled.
I haven't come across any other references to sugar curdling milk in this way. I have only seen it referenced as a 'stabiliser'.
I assume that the curdling was made more likely by my milk's low fat content. I was not stirring constantly. But I'm not looking for a fix, just for understanding. I didn't really want to get it 'right'.
So, could someone please explain what most likely happened here? Is it simply that milk heated with a high enough proportion of anything that dissolves in water will separate and curdle within minutes? Or is is something specifically to do with sugar?
Specifically, what was it about the sugar that I added that caused the milk to curdle (the amount? something else?), and what is the nature of the curdling process? (The second question has been answered elsewhere, but it may be relevant in answering the first, which has not been asked elsewhere).
Thank you for any advice. I know that next time, when I follow a recipe and want to get it absolutely right, I'll have a better understanding of what's going on, thanks to your answers.
P.S. In the end I strained the mixtures, reserving the very sweet solids, and continued to reduce the sugar/milk liquid mixture until I ended up with something very similar in taste, colour and consistency to condensed milk.
Best Answer
It's not the sugar that caused the milk to curdle, it's the milk itself. Dulce de leche and caramel are both usually made with either cream, condensed, or evaporated milk. The issue with regular milk (especially skim), is that it has such a high water content and low fat content. The fat in cream buffers the protein, helping to prevent curdling, and the canned milks have already had most of the water removed, making them less likely to curdle.
The sugar could also have a buffering effect on the milk protein, unfortunately you have a catch 22. In order to buffer the milk form curdling, the sugar would have to be dissolved in the milk. In order to dissolve sugar in the milk at a 1:1 ratio, the milk would have to be heated past the point where it would curdle.
You might be able to prevent this by using a double boiler until the milk has reduced a lot. Making a caramel requires almost all of the water to be cooked out of your syrup, so this will take a really long time and isn't advisable.
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Quick Answer about "What causes curding in this case: heating milk with large quantities of sugar"
After much experimentation, we discovered it was the brown sugar. More specifically, the molasses in the brown sugar. Any acid will cause milk to curdle.Why does milk curdle when sugar is added?
Because of the acids, molasses or even brown sugar will make milk curdle if you boil it with either of them. For this reason, many recipes for butterscotch sauce, and particularly for butterscotch pudding, begin by cooking the brown sugar with butter before adding cream or milk--especially milk.Why did milk curdle when heated?
The Science of Curdled Milk Milk is a mixture (called an emulsion) of butterfat, proteins, and water. When milk is boiled, the three components of the emulsion break apart: the milk proteins coagulate and separate from the water, producing what is commonly known as curdled milk.What happens when you boil milk and sugar together?
Boiling temperature of milk is 212.2\xb0, very similar to water. The boiling temperature of sugar and water, goes up by 1/2 a degree per 180 grams of sugar, starting at 212\xb0. so with the sugar included, the milk mixture boiled slower. This time, Dr.Why does my milk keep curdling?
Warmer temperatures and frequent fluctuations can put food at risk of spoiling, especially milk and cream. Although a gallon or half gallon of milk may fit perfectly in the fridge door bins, the warmer temperatures may make the liquid curdle before you can drink it.\
More answers regarding what causes curding in this case: heating milk with large quantities of sugar
Answer 2
It might not be the sugar curdling the milk, but just the milk curdling itself. SourDoh mentioned the possibilities linked to the lower amounts of fat, but there's also the possibility of the milk's age playing a role - fresher milk may well solve the problem.
When milk curdles when heated, it is usually linked to acids, or spoilage, but it can happen even in otherwise good, plain milk if that milk is on the older side. This milk is often fine for cold applications, not spoiled or anything, it just can't be heated without separating at this stage - so no good for tea or coffee.
I think it's a bit more likely to happen with older milk, not gone bad but getting near that point and at the end of its shelf life... milk slowly gets more acidic as it ages and bacteria work on it, and there's a point where it hasn't spoiled, but will fairly soon, that can be acidic enough to curdle itself when heated.
You can check if it's the milk by heating a bit by itself, in a pan or even the microwave, to see if the milk proteins clump up.
Answer 3
Salt!!
my caramel started curdling and I couldnt figure it out, then it hit me - I had started adding salt earlier, for ease. I held off on salt til the sauce was done, and boom!, bob's your uncle. lol
From the web: Salt is another ingredient that can cause milk to curdle. But?, obviously, you need to season your sauce. The key is to add the salt at the end, rather than cooking or reducing it with the salt already in it. Apr 4, 2017
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