Certain recipes specify that you use a Spanish onion, but what exactly is a Spanish onion? A lot of cooks are at a loss as to what this means and reach for a red onion. But no, Spanish onions and red onions are quite distinct in both appearance and taste.
Spanish onions are characterized by their large size, pale brown skin, and sweet flavor (although they are not as sweet and mild as "sweet" onions such as Vidalia). They are not a separate species, but a variety of the common onion. It is not known where the name Spanish came from, although this onion did originate in the Mediterranean region. It was likely cultivated by the ancient Egyptians and Romans. They are usually grown in soils that contain a low level of sulfur, which is a major reason for their mild taste and smell.
Lacking a true Spanish onion, what should you use? In cooking, an ordinary yellow onion is a close sub. For raw uses it would be better to use a true sweet onion such as Vidalia, Walla Walla, or Maui.
Thanks for this bit of onion info