How can I prevent curdling when adding fruit to milk?

Question

I've recently started making simple desserts consisting of milk, sugar, flavoring and gelatin. Last time I tried using frozen raspberries as flavoring (around 1:10 raspberries to milk by weight) and the milk curdled. It still tasted good, but the presentation was less than appealing. Is there some ingredient I can add to the mix or some special technique I can use to prevent curdling?

As long as the last step is "bring to boil, mix in gelatin and set aside", I think, that any process will work.

One obvious solution I want to avoid is neutralizing the acid with a base. I don't like this, because I would need to adjust the amount of the base to the acidity of the flavoring: if I overdo it, then milk will curdle from the alkalinity, if I underdo it, then it will still curdle from acid. It's too precise for my liking if there is another solution available.

_{This was my experience using soy milk, but I've found people on the Internet saying it happened to them with cow's milk, so "milk" in this question refers to both cow's and plant milk. I use both soy and cow's, so I'm interested in answers for both.}

Answer 1

All you have to do is to make sure you don't acidify your milk. It curdles with acid; the procedure you describe (adding fruit that exudes acidic juice, then bringing to a boil) is basically a recipe for paneer.

This means that you have to pick your ingredients carefully. Frozen raspberries are not suitable for what you have in mind. Their juice will flow out while they warm up.

Instead, you should use fresh raspberries. Prepare the milk with the gelatine and sugar (no need for boiling, 40-50 C is sufficient and even preferred for gelatine), add your never-frozen fruit to the cups, and then pour the still warm milk-gelatine mixture over it. This will create the dessert without curdling of the milk and without your fruit changing its taste from boiling.

Other kinds of fruit besides raspberries will work similarly with this procedure, there are very few which aren't feasible at all.

There are a few flavors which will work better if boiled, e.g. pumpkin, spices, or herbal extractions. For those, you can keep the boiling procedure - they shouldn't curdle the milk anyway.

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If you really don't want to use fresh fruit and want to add something, you can add more sugar. Especially if you cook the fruit into a jam first (just standard sugar-and-fruit preserve, no pectin added), it won't curdle the milk when mixed with it. A base isn't optimal. I don't think it would curdle the milk, but it will change the taste in unpleasant ways.

Answer 2

When you are adding the acidic ingredient is not clear from your description, but curdling usually happens when the acidic ingredient is added to a dessert base that is 145F (63C) or hotter. Either add the acidic ingredient when everything is cold or cool the heated ingredients below the indicated temperature. That should keep things from curdling.

Answer 3

If you object to neutralizing the acid, the only other solutions I can imagine are:

1. "Use less fruit" so that there is less acid relative to the overall mixture.
2. "Change from milk to yogurt" (or make the milk into yogurt) so acidity and a (generally considered) more appealing form of "curdling" have already been taken care of.

Answer 4

I prepare orange milk pudding and the milk does not curdle. The thickened milk has to be cooled completely and then we add orange juice and pulp into the milk. The milk does not curdle.

If the orange is too sour or any fruit in your case, add sugar to the fruit and keep till it melts. Then you add.

Answer 5

Another solution is that You may add citrate to milk to increase it's salt balance which will give it resistance from spoilage