12 Tbsp Sugar
,300 ml Milk
4 eggs
250 ml. Whipped Cream
1 Tbsp cornstarch
I make a caramel with half the sugar, I add the milk to it. Then I mix the cornstarch with the egg yolks and I add it to the milk/caramel. Once it cools down I fold in the egg whites and whipped cream.
Short version of my thoughts, followed by a detailed explanation in case you want the reasoning.
- Cook egg yolk, cornstarch, and cream to 210°F. Do not cook above 212°F.
- Use a heat resistant spatula
- Stir very gently and slowly.
- Use regular whipping cream, not heavy whipping.
- Increase the cornstarch
- Reduce the egg whites
- Try stabilizing whipped cream with a bit of gelatin
Long explanation for the above troubleshooting suggestions...
The first thing I noticed is there’s no stated temperature for heating the custard mixture. Mousse starts with a custard base, so cooking temperature is a key component is a successful mousse.
The type of thickener determines cooking temperature.
Cornstarch is problematic since mousse contains egg and whipping cream.
Egg yolks contains an enzyme called amylase.
Cornstarch contains an enzyme called amylose.
When cornstarch thickens, it’s amylose molecules bind into a long chain. If the amylose chain is broken, the mixture thins out.
Now let’s go back to egg yolk enzyme amylase. Amylase is designed to break down amylose. And it’s very good at it.
If I understand your process correctly, you’re simply mixing the cornstarch into the egg yolks, then blending it into the warm caramelized sugar and cream. You’re not cooking the egg yolk at all. That won’t work if you use cornstarch. You need to cook the yolks to kill the amylose.
Amylase molecules like it hot. It is most effective at breaking up the cornstarch chain of amylose at temperatures between 155°F – 185°F. Most custard bases are heated to 180°F—the perfect temperature for amylase to seek and destroy.
In order to protect the cornstarch’s amylose chains, you have to destroy the enzyme in the egg yolk.
If it’s not destroyed, the enzyme breaks down the cornstarch as your mixture cools. So you start with a thick mousse, then several hours later it’s runny.
As I mentioned above, custards are normally heated to 180°F. But the use of cornstarch means you have to heat the mixture hot enough to kill the egg enzyme. Heat the the mixture to 210°F and hold it there for a minute to destroy the egg’s amylase.
It’s extremely important you do not heat to 212°F ! That is boiling temperature at sea level. Too high a temperature will cause the starch cells to burst. So again, once cooled, it will lose its thickening power.
NOTE: If you live at high altitude, the boiling temperature will lower than 212°F. So heat two degrees below whatever is boiling temperature at your altitude.
Another issue with cornstarch as a thickener is it breaks down with a lot of stirring. Cooking the egg mixture requires constant stirring to prevent the egg yolk from turning into scrambled eggs. So stir slowly and gently. Use a spatula or spoon. Do not use a whisk.
Still another problem with cornstarch is it thins after cooling when there’s too much fat in the mixture. Heavy whipping cream contains 35% fat—which is too high for cornstarch. Use regular whipping cream, which has around 30% fat.
Another thing to keep in mind is the human mouth contains the same amylose enzyme as eggs. Amylose is how the human body breaks down starch and convert it to sugar. If you taste while mixing, always use a clean spoon and never reuse a spoon. I know that’s basic food hygiene, anyway. But some people don’t adhere to those standards. I have a friend who sticks his used spoon in the pot. Needless to say I won’t eat anything he cooks.
One last thought on cornstarch. One tablespoon of cornstarch weighs about 8g. You have 550ml liquid, plus the natural water in the eggs. I think you should try increasing the cornstarch.
Also, egg whites are 90% water. You might try reducing the amount of egg whites.
Finally, since you want to pipe the mousse, you could try using whipped cream stabilized with a bit of gelatin.
I do not know if your ratios will produce a nice thick mousse. Your mixing method is not how mousse is traditionally made. But I think that’s where the problem is; to create a stable mousse, you have to use standard methods for a stabilized custard base since that’s the foundation of a mousse.
