As I know the verb "taste" isn't normally used in Present Continuous. But I have one example when it's used. Is it correct? Why? If I use the Present Simple here, is it not correct?
The reason I get fat is that I'm always tasting things while I’m cooking.
The reason I get fat is that I always taste things while I’m cooking.
"Taste" as a verb is used in two ways:
This milk tastes sour.
Here the subject is the food and "taste" is a linking verb. You don't use present continuous in this sense
I taste the milk before I drink it.
Here the subject is the person, and the object is the food. In this sense the present continuous is correct.
John is tasting the chicken, and he is smiling! It must be good.
In your situation, you are describing a "general fact" so you would normally use the simple present tense.
I always taste the food while I'm cooking.
The present continuous might be used for nuance or just to add variety and immediacy. It suggests, perhaps, repeated samples of the food.
Both are correct uses, but there is a slightly ambiguous meaning because of taste:
I'm always tasting food while I'm cooking.
can mean
"Whenever I cook food, I make sure it's up to my standards by sampling it first."
but it could also mean,
"Whenever I cook food, I experience the strange sensation of it being in my mouth, despite not eating anything."
In this example, most speakers will assume you mean something like the first sentence instead of the second.
As I know the verb "taste" isn't normally used in Present Continuous.
It's generally fine to use taste this way. If you wanted to eliminate any ambiguity I would try a different verb:
The reason I get fat is that I always sample things while I’m cooking.
