Huaniu apples sometimes go bad and turn yellow inside. This is because there is still iron in the apples, which may be oxidized. Fe3O4 is yellow. Huaniu apple is a specialty of Tianshui City, Gansu Province. It refers to the superior variety of Marshal apples produced in most areas of the city and is a national geographical indication product of China. The meat of the product is fine, dense, crispy, juicy, unique in flavor, rich in aroma, good in taste and of high quality. It is recognized by many Chinese and foreign experts and marketers as one of the world's three most famous apple brands, along with American Snake Fruit and Japanese Fuji. It is China's first Apple brand to obtain an official trademark in the international market. On October 20, 2016, the State Administration for Industry and Commerce recognized "Huaniu Apple" as a "China Famous Trademark". In 2018, the trademark "Tianshui Huaniu Apple" was applied as a national geographical indication certification trademark.