The big question for mead-makers is "Sweet or Dry?". Though mead is often thought of as a sweet drink, everyone has their own preference, and you as a mead-maker get to decide what you like. Dry mead can be absolutely spectacular by displaying a very pure representation of the ingredients. Sweet mead has the wonderful honey sweetness that many drinkers are looking for in a mead. A semi-sweet mead is between the two and can have the best of both worlds. There are a few ways to adjust the sweetness of your mead. We'll start by explaining how the alcohol tolerance of the yeast can be used to make sweet mead.
Though mead is similar to wine in many ways, it differs greatly when it comes to the starting and finishing gravities. Wine is usually limited by the sugar that the grapes can provide, which keeps most wine in the 1.080-1.110 range, or about 12-15% alcohol by volume. Most wine yeast can handle this alcohol content range without trouble, and usually will ferment the wine dry, meaning no or very little sugar remaining. On a hydrometer this is somewhere in the range of 0.994-1.000 or so.
Honey is so concentrated that you can make your starting gravity whatever you'd like. This means that you can easily start out at 1.140, for example. If a mead of this sugar content were to ferment dry, it would be over 19% alcohol! Most wine yeasts, however, cannot withstand this level of alcohol and will stop fermenting before all the sugars are gone. That means that some sugars will be left over, which will make the mead sweet or semi-sweet. By paying attention to your yeast strain's alcohol tolerance level, you can select a strain and starting gravity that give you the desired level of sweetness remaining. The Lalvin 78-B Narbonnes strain is an excellent one for making sweet meads in this fashion, as it has a relatively low alcohol tolerance and makes a mead that is usually ready to drink relatively quickly.
This method is not an exact science; depending on the conditions yeast can stop before or after their usual alcohol tolerance level. In addition, mead has a finicky way of starting back up again just when you think it's done fermenting for sure. An alternative method of making sweet mead is to use potassium sorbate, a chemical that prohibits further fermentation. Potassium sorbate cannot stop a fermentation that is in progress, but if you have a completed fermentation, using potassium sorbate allows you to add additional sugars back to the wine without the yeast starting up again. You should still age the mead after sweetening to make sure that all fermentation has stopped (the gravity should remain constant). If you are planning to use potassium sorbate, it is a good idea to use potassium metabisulfite from the beginning of the brewing process. Sulfite will prevent malolactic bacteria from getting in your mead, and the combination of potassium sorbate and malolactic bacteria can produce some unwanted, "geranium" like off-flavors.
Sweet meads can be anywhere up to about 1.040 in finishing gravity. Very sweet and strong meads are sometimes called "sack" mead. The sweetness is usually balanced by the alcohol content as well as the acidity. If you wind up with a mead that is too sweet adding some acid can help balance it out, our acid blend is a good option. If you are back-sweetening, or adding sugar/honey to an already fermented mead as in the potassium sorbate method above, you can add honey to taste by adding it in small increments and taking samples.
If you are trying to make carbonated sweet mead, forced carbonation with co2 is the only way to go. Trying to add priming sugar to it won't work, as the yeast cannot consume the remaining sugars. Trying to time the bottling to have just enough sugar remaining to carbonate is a recipe for disaster and potentially very dangerous. Using a kegging system and a co2 tank works quite well, however, and is the easiest way to reliably carbonate any mead.