Hello MangNestor. It is wonderful that you are keeping the tradition of whole grain porridge alive, though I completely understand how frustrating it is when a batch turns out bitter.
In most cases, bitterness in millet comes down to the natural oils present on the surface of the grain. Millet contains delicate unsaturated fats that oxidize quite easily when exposed to air. When these surface oils oxidize, they leave behind a thin, bitter residue on the outer hull.
To prevent this, traditional culinary methods always emphasize thorough washing and scalding before cooking. First, place your dry millet in a fine-mesh strainer and rinse it thoroughly under warm or hot running water, gently rubbing the grains between your hands. The heat helps dissolve and wash away those oxidized surface oils. A time-tested traditional trick is to pour boiling water over the raw millet in a bowl, let it sit for two to three minutes, and then drain it completely before adding fresh water or milk for cooking.
Another helpful traditional step is to lightly dry-toast the rinsed and dried grains in a pot over medium-low heat for a couple of minutes until you smell a pleasant, nutty aroma. This rounds out the flavor and brings out its natural sweetness.
Lastly, because millet fats oxidize relatively quickly compared to other grains, always store your dry millet in an airtight container in a cool, dark pantry or even the refrigerator, and check that the raw grain smells fresh and sweet before you start cooking.
