Sulphured molasses is made from young sugar cane. Sulphur dioxide, which acts as a preservative, is added during the sugar extraction process. Unsulphured molasses is made from mature sugar cane, which does not require treatment with sulphur. There are three grades of molasses: mild, or first molasses; dark, or second molasses; and blackstrap. These grades may be sulphured or unsulphured. To make molasses, the sugar cane plant is harvested and stripped of its leaves. Its juice is extracted from the canes, usually by crushing or mashing; it can also be removed by cutting. The juice is boiled to concentrate it, which promotes the crystallization of the sugar. The result of this first boiling and removal of the sugar crystals is first molasses, which has the highest sugar content because comparatively little sugar has been extracted from the source. Second molasses is created from a second boiling and sugar extraction, and has a slight bitter tinge to its taste. The third boiling of the sugar syrup makes blackstrap molasses. The majority of sucrose from the original juice has been crystallized, but blackstrap molasses is still mostly sugar by calories. However, unlike refined sugars, it contains significant amounts of vitamins and minerals. Blackstrap molasses is a source of calcium, magnesium, potassium, and iron; one tablespoon provides up to 20% of the daily value of each of those nutrients. Blackstrap, often sold as a health supplement, is also used in the manufacture of cattle feed and for other industrial uses.