A few things can cause tomato sauces to become bitter:

• Overcooked spices. Both basil and oregano can become bitter with long simmers. Add them later in the process.
• Under-ripe tomatos. Store bought tomatoes are often picked green and ripened in the store. These tomatoes make less sweet sauces (which may be contributing).
• Cooking in an aluminium pan. Aluminium reacts with the acid in the tomatoes and adds an off-putting flavour.
• Seeds/skin in the sauce. Both seeds and skins can be bitter.

You can improve a bitter sauce by adding a small amount of baking soda (or salt), and something sweet (but not too much).

A few things can cause tomato sauces to become bitter:

• Overcooked spices. Both basil and oregano can become bitter with long simmers. Add them near the end of the process.
• Under-ripe tomatos. Store bought tomatoes are often picked green and ripened in the store. These tomatoes make less sweet sauces (which may be contributing).
• Cooking in an aluminium pan. Aluminium reacts with the acid in the tomatoes and adds an off-putting flavour.
• Seeds/skin in the sauce. Both seeds and skins can be bitter.

You can improve a bitter sauce by adding a small amount of baking soda (or salt), and something sweet (but not too much).