The reason why you should take the skin off of roasted peppers is because taking the skin off of the roasted peppers improves the taste, texture and digestibility of the roasted peppers.
Roasting the peppers dries out the outer skin of the peppers and separates it from the flesh and turns into a tough, papery membrane which gets stuck in your teeth, and the outer peel of the roasted peppers is also highly fibrous, which does not dissolve or blend smoothly into soups, dips or purees.
And so leaving the skin on the roasted peppers, often results in rubbery and unpleasant fragments.
The goal of roasting the peppers is also to blister and blacken the exterior of the peppers and while this does char the skin, eating the actual burnt skin of the roasted peppers tastes ashy, unpleasant and bitter.
And the rich, smoky and caramelized sweetness of the pepper also remains locked entirely within the soft inner flesh and peeling the roasted peppers, removes the harsh bitterness without losing the roasted flavor.
The outer skin of peppers is also tough and difficult to digest for the human body as they can be hard to break down inside the body.
When cooking peppers in the oven the peppers takes around 25 to 40 minutes in the oven at 400 F.
You should cook the peppers in the oven at 400 F for 25 minutes to 40 minutes until the peppers become tender and charred.
Sliced peppers often need between 25 minutes to 35 minutes in the oven at 400 F and whole peppers need around 35 minutes to 40 minutes.
For sliced and diced peppers, you should roast the sliced and diced peppers for 25 minutes to 30 minutes and stir halfway through for even browning.
For whole and halved peppers, you should roast them for 35 minutes to 40 minutes until the skin is blistered and charred.
For easier peeling of the peppers, after roasting the peppers you can place the peppers in a bowl and then cover it for 10 to 15 minutes to steam, which makes the skin pull way from the peppers easier.
Peppers don't usually get hotter if you roast them, and instead when pepper are roasted they often taste less intensely hot.
However when you do roast the peppers, the flavor of the peppers becomes more intense as well as complex.
Roasting the peppers does concentrate the capsaicin in the peppers by removing the water, but the extended heat and the steam from roasting the peppers breaks down the heat compounds, which makes the roasted pepper milder and not as hot as it normally would be.
When you roast the peppers, the roasting of the peppers enhances the natural sugars in the peppers and creates a smoky, sweet as well as complex flavor, which can also feel less jarring than the normal, sharp, raw heat of a fresh hot pepper.
And while removing the water from the peppers when roasting them, concentrates the spice in the peppers, the heat itself in the pepper is steam volatile and will break down with sustained cooking or roasting, which results in a milder pepper, instead of a hotter pepper.
If you want the mildest flavored pepper when roasting them, you should roast the peppers thoroughly for around 5 minutes at 500 F.
Boiling the peppers also reduces the peppers heat significantly, because the capsaicin leaks into the water during the boiling process.
And similar to that of roasting the peppers, frying or sauteing the peppers can also make the peppers feel less intense over time, although it can also cause the capsaicin in the peppers to become airborne and act like a tear gas for example in the kitchen or where you're cooking the peppers.
If you want the peppers to maintain their maximum heat the peppers should either be consumed raw or lightly cooked instead of fully cooking them or roasting them.