When buying leather eggs, what's the difference between yellow and black? Which one is better?

From the production process, the difference between yellow hearted and black hearted leather eggs is the content of edible soda ash and external lime, the former has a lower content, while the latter's content is a little higher, so the production of two results. A yellow or red heart, a black heart, but both have no problem, both can be safely eaten. At the same time, yellow eggs are mostly made of eggs, egg white and yolk ingredients less, placed for a short period of time, known as "change eggs". While the black eggs are mostly made of duck eggs, egg white and yolk ingredients are heavier, placed for a long time, the ingredients added pine and cypress branches, known as "pine eggs".