It has been almost ten years since I tried "miracle fruit" and I'll never forget it. The little red berry, the only fruit on the bush, was split three ways. It tasted like, well, nothing. I didn't think it was much of a miracle.
After consuming a large bowl of lemons, followed up with another bowl of oranges, we were convinced of the miraculous nature of that fruit. Those were the sweetest lemons I have ever had.
I've since tried to explain the situation to others, and even to find information on the fruit on the internet to no avail.
It seems that Japanese scientists have engineered lettuce to contain the protein that binds to your taste buds and make sour things sweet.
The protein is called miraculin, and the fruit it occurs in naturally is called Richadella dulcifica, or "miracle fruit".
Super Lettuce Turns Sour Sweet