Smooth firm, well shaped parsnips of medium size generally have the best quality.  Soft, shriveled, fibrous, or pithy roots are considered sub standard. Softness sometimes is an indication of decay, which may appear as gray mold or watery soft rot.  Woody cores are often found in large, coarse roots.  Misshapen roots have low yields and should be avoided.  The parsnip is a winter vegetable and its flavor does not fully develop until it has been exposed to temperatures near freezing.  Exposure to cold develops the sweet flavor needed in a quality Parsnip.  Scientist say that the low temperatures change the starch in the root to sugar and at least 2 weeks of freezing temperature is needed to develop the flavor quality needed.