Research Reveals What Makes Bell Peppers Turn Red Researchers have deciphered in detail at the protein level what makes these fruits turn red as they ripen December 14, 2020 Green bell peppers are unripe and do not fully ripen. Bochum biologists want to know why. Bright red, tasty and healthy, that’s how we know and love bell peppers. In a first, the team headed by professor Sacha Baginsky from the Chair for Plant Biochemistry at Ruhr University (RUB) has deciphered in detail at the protein level what makes them turn red as they ripen. At the heart of the project are the so-called plastids, typical plant cell organelles in which chlorophyll is broken down and carotenoids are produced as the fruit ripens.