This is caused by the way the pine nuts was processed. I was born and brought up in China. Pine nuts were always bitter. They were sold as sugar covered candies. The thousand years of process method couldn’t prevent the contamination from the taste of pine corn. Since in most cases, bitter taste from the natural food is from Vitamin C, Chinese people live with the taste. They choose bitter melon and tea for the same reason. It prevents the sour taste in the mouth after eating food, and lower your expectation for sweets.
After I came to US, I was surprised to find out that pine nuts are actually a little sweet. We need to help them to improve the process in China by our technology. The bitter taste we feel may not be an issue over there.