White grains (of fat or egg whites?) on chocolate mousse

Every time I make chocolate mousse it gets delicious and essentially fine in every aspect. But there is one thing that annoys me: it is always full of slightly perceptible white grains/flakes of what seems to be the cream or the whipped egg whites.

My suspects:

• I’m mixing the ganache part of the mixture too early with the whipped whites (meringue), so that the whites may be getting slightly cooked in the process;
• or, maybe, the fat content (35%) of the cream I’m using is too high (may be chance, since I don’t remember details, but I once used a 20% fat cream and this problem didn’t happen, even though the resulting mousse was not as delicious and firm).

To clarify, I make it by carefully mixing a 50/50 ganache (100g 30%-35% cream and 100g 40%-50% cocoa chocolate) with meringue (3 egg whites whipped until reaching the propper meringue aspect, then mixed with 6 tablespoons of white sugar).

the white grains slightly noticeable on the top of the mousse here are all around, in and on it, and they are not air bubbles. (Sorry, cellphone camera is kinda horrible)