Sweet Potatoes or yams?
ONE SIMPLE RULE – THE YAMS YOU BUY ARE PROPERLY SWEET POTATOES ALL ALONG
Most people do not know or even realise there is a difference between a sweet potato and a yam. If you are in the UK the word yam does not even enter your lexicon. What the Americans often call a yam is a sweet potato there. On the off chance you find a real yam it will most likely be in an ethnic market of a big city with a large population from other countries.
The reality is that most Americans and Europeans in fact anyone from the northern hemisphere has actually never had a true yam before in their life.
Sweet potato and yam are both tuberous root vegetables that grow as a flowering plant but they are NOT related.
THE TRUE YAM (DIOSCOREA GENUS)
Coming from Africa and Asia, Yams can be quite small or extremely large in size. One major difference between a yam and a sweet potato is the former is much drier and starchy. They belong to the Lily family. It has a rough skin (almost scaly) and notably low amounts of beta-carotene compared to the sweet potato. If you find a true yam in a US market its most likely been imported from the Caribbean.
THE SWEET POTATO
Sweet potatoes are part of the Morning Glory family. Skin colour can range from lighter varieties (white and yellow) to darker (red, purple and brown) with the same spectrum of flesh colour variety. They are distinctive because of their elongated shape and tapered ends.
It is said the confusion of calling sweet potatoes as yams arose because of the need to differentiate the soft varieties from the firm varieties. It might have been a better idea to name the latter ‘softer’ sweet potato in hindsight. A basic distinction can be made if you are going to shop for them in the US.
Yam — Soft sweet potato with a copper skin and deep orange flesh.
Sweet potato — Firm sweet potato with golden skin and lighter flesh.
Different sweet potatoes cook differently. After cooking firm sweet potatoes still remain firm and a little waxy, while the soft variety becomes creamy, fluffy, and moist. So to avoid problems when buying your yams/sweet potatoes take into account how you will be using it and then decide with your eyes and touch which is for you.