from oxidizing, potassium metabisulfite and potassium sorbate are added. After the mead clears, it is bottled and distributed. Primary fermentation usually takes 28 to 56 days, after which the must is placed in a secondary fermentation vessel for 6 to 9 months of aging. Durations of primary and secondary fermentation producing satisfactory mead may vary considerably according to numerous factors, such as floral origin of the honey and its natural sugar and microorganism contents, must water percentage, pH, additives used, and strain of yeast, among others. Although supplementation of the must with non-nitrogen based salts, or vitamins has been tested to improve mead qualities, no evidence suggests that adding micronutrients reduced fermentation time or improved quality. Cell immobilization methods, however, proved effective for enhancing mead quality. Varieties Mead can have a wide range of flavors depending on the source of the honey, additives (also known as "adjuncts" or "gruit") including fruit and spices, the yeast employed during fermentation, and the aging procedure. Some producers have erroneously marketed white wine sweetened and flavored with honey after fermentation as mead, sometimes spelling it "meade." This is closer in style to a hypocras. Blended varieties of mead may be known by the style represented; for instance, a mead made with cinnamon and apples may be referred to as either a cinnamon metheglin or an apple cyser. A mead that also contains spices (such as cloves, cinnamon or nutmeg), or herbs (such as meadowsweet, hops, or even lavender or chamomile), is called a metheglin . A mead that contains fruit (such as raspberry, blackberry or strawberry) is called a melomel, which was also used as a means of food preservation, keeping summer produce for the winter. A mead that is fermented with grape juice is called a pyment. Mulled mead is a popular drink at Christmas time, where mead is flavored with spices (and sometimes various fruits) and warmed, traditionally by having a hot poker plunged into it. Some meads retain some measure of the sweetness of the original honey, and some may even be considered as dessert wines. Drier meads are also available, and some producers offer sparkling meads. Historically, meads were fermented with wild yeasts and bacteria (as noted in the recipe quoted above) residing on the skins of the fruit or within the honey itself. Wild yeasts can produce inconsistent results. Yeast companies have isolated strains of yeast that produce consistently