I used onion canned tomatoes with herbs tomato paste and oregano ,garlic and onions .I sauteed the onions and garlic added the tomatoes let that cook for a while and then the tomato paste and some water .volia Brown .
my pasta sauce turned Brown .WHY ?
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May be your sauce was overcooked. May be you caramelized the onions. May be the tomato paste is too much concentrated.
quite possibly, onions over browned and deglazed with wine. generally, you will find that if the onions caramelise to much, the wine will lift the onion caramel and leave it in the sauce. With a tomato based sauce, it shouldnt be so pronounced, but it will be there.