Yeast is in my mind the most important part of the process for making your own hard cider or wine after using properly-sanitized equipment and good-quality ingredients. The reason is simple: without yeast, there is no fermentation to turn the sugar into alcohol and excrete CO2 (carbon dioxide), which is needed to carbonate your beer or sparkling cider when you bottle.
In this article, I'll tell you about three of my favorite yeasts I use in my own kitchen.
Sweet, Or Sour?
In order to choose the right yeast for the job, you first have to know how you want your hard cider or wine to turn out. Are you looking for a sweet cider that has a lot of "apple character," or are you looking for something that tends to sour or bitter? Yeast isn't the only determining factor in the process, but it plays an important part. So, you have some choices to make.
For example, a yeast that consumes more sugar will make for a "dryer" wine or cider. For a sparkling (carbonated) cider, you'll want to use a yeast that's fairly aggressive in its consumption of the sugar - the less sugar, the "dryer" the cider. Also, an aggressive yeast can produce more CO2, meaning more bubbles. I prefer naturally-produced carbonation over fermentation that is created after the fact by CO2 injection or carbonation tablets - a much more pleasant sensation on the tongue!
Let's go through some options.
My favorite yeast for dry, sparkling ciders is Lalvin's EC-1118 yeast. EC-1118 is a champagne yeast that consumes almost all of the sugar in a vigorous fermentation, so you're going to have lots of bubbles. Also, EC-1118 has a higher alcohol tolerance than other yeasts, so if you're wanting to produce a cider with a high ABV (percentage of alcohol by volume) this is a good one to use.
Because EC-1118 consumes almost all of the sugar in the apple juice, the resulting cider is going to be very dry - sour/bitter. If you're going for the higher alcohol content but aren't all that thrilled with "pucker power," what you might consider doing is not carbonating the cider (stop the fermentation before you bottle - easily done with Campden potassium metabisulfate) and then back-sweetening as you bottle. In some locales, the cider will be left unsweetened, and will be mixed with a lemon-lime soda pop when served, which will add bubbles and some sweetness.
If you're serving this cider with a meal, any food that goes well with a dry champagne will go well with this dry cider. As with everything, you know your tastes the best, so experiment until you find the best way for yourself.
Sweet, Lots of Apples
Taking things to the other side of the spectrum... a sweeter cider with lots of apple character can be had by using an ale yeast for the fermentation. The yeast I recommend as a good starting point is Danstar's Nottingham Ale Yeast. This is also a vigorous yeast, but the end result will be an ale-like taste that retains more of the apple flavor than EC-1118.
Right in the Middle
If you're looking for a nice semi-dry (sweet with a little bite), try Lalvin's K1-V1116 yeast, which is commonly used for semi-dry white wines. K1-V1116 is a very versatile yeast that will produce a wine or cider that has a fresh taste, and can be especially good for wines or ciders that are started from concentrate, which won't have the natural yeast nutrients that will come from raw fruits. It's also able to tolerate a very wide temperature range (Lalvin's website states that K1-V116 will do well from 50o to 90o Fahrenheit). If you do your fermenting in a place without much climate control, this is a great yeast that will produce good results even when conditions aren't ideal.