To add cream to your soup without curdling you need to first warm up or temper the cream by gradually whisking a small amount of hot broth into the cold cream to temper it and then slowly add the tempered cream back into the hot broth or soup while stirring continuously.
What this does is brings the cream closer to the temperature of the broth or hot soup before you add it all at once to prevent curdling of the cream.
You can add cream to boiling liquid as long as you temper the cream before adding it to the boiling liquid.
You should also use high fat cream instead of low fat cream as low fat cream will often curdle when added to hot liquid.
Heavy creams and whipping creams can be added to boiling liquid without curdling due to their high fat content.
You cannot add cold cream to hot soup as the cold cream will curdle.
If you want to add cream to hot soup you should temper or warm the cream by slowly whisking the cream into some of the hot liquid.
After the cream is warm then you can add it to the hot soup.
Use a high fat cream when adding it to hot soup as heavy cream or whipping cream is less likely to curdle than low fat cream or low fat milk or half and half.
You can also add a little flour to stabilize the dairy and prevent curdling.
Adding some yogurt or coconut milk can also work in hot soups.
Coconut milk can be added directly to hot soups without tempering as it's non dairy and plain yogurt can add a lighter and tangy flavor to the soup.
If your recipe calls for adding cream to an already hot soup or sauce, you should always temper it instead of just pouring the chilled cream straight into the hot broth.
You should also turn down the broth to a low simmer.
And then take a tablespoon or so of the hot broth, add it to the cream, and stir it in.
If you started your soup with broth, stock or water, you should ideally wait until the end to add the cream.
You can also warm the cream, or “temper” the cream.
Take about half a cup of the hot broth and slowly add your cream to that, stirring constantly.