Mead is more a wine than beer, with a final alcohol level anywhere between 10 and 18 percent. Wine yeasts, which have a higher alcohol tolerance, may ferment slower at first (although some are remarkably fast) but will ferment more completely than ale or lager yeast. They are also less likely to produce “off” tastes which take a long time to age out after the mead is finished. A partial list of some of the popular yeasts are: Champagne (multiple strains), Epernay, Flor Sherry, Steinberg, Prise De Mousse, Tokay, and various proprietary strains which are derived from these
This list is by no means exhaustive. Each yeast will impart its own unique characteristic to the mead. Champagne ferments out very dry and has a high alcohol tolerance. Epernay has a fruity bouquet. Flor Sherry has a high alcohol tolerance and contributes a flavor that goes better with sack meads. Prise de Mousse is particularly neutral, fast-fermenting, and attenuative (leaves little residual sweetness). Some yeasts (such as Montrachet wine yeast) can produce noticeable levels of phenols (the throat-burning part of cough medicine), which age out eventually in bottle conditioning but are an unnecessary complication since there are yeasts that don’t produce them.
Honey by itself is low in some of the nutrients that yeast need to reproduce and quickly ferment out the mead must. Fermentation times can be measured in months as the yeast slowly trickles along. This is a disadvantage because as long as the fermenting mead remains sweet and low in alcohol, it is inviting to contaminating bacteria and lacks a good layer of carbon dioxide (CO2) to protect against oxidation. Mead makers can add a nutrient to help the yeast, and normally should do so if the only fermentable ingredient is honey. Fruit, particularly grapes, will contribute needed ingredients; thus melomels have lesser or no requirement for nutrients. Nutrients are normally added when the must is prepared.
There are several kinds of nutrients. Most winemaking shops will sell various salts designed for grape musts. While this is helpful for mead, too much can leave an astringent metallic flavor that will take months or years in the bottle to age out. Yeast extract, pulverized yeast, is also available. Dead yeast are exploded ultrasonically or in a centrifuge, and sold as a powder. Yeast extract will not leave the same metallic flavors as nutrients, but may be more difficult to find. It is not possible to make your own yeast extract at home.