I’ve been experimenting with cider for many years. I’ve had a few really great ones, and a lot of ones that went bad (rubbery or turpentine flavors), or turned to vinegar… which isn’t all bad… I save the vinegar for all sorts of household uses and salad dressings. Still have a couple gallons of good stuff ready to bottle though from last October.
I believe I have experienced malolactic fermentation before, just by leaving the cider sitting for 6-9 months before bottling. It steadily loses acidity over time, which I can only assume is from malolactic bacteria. Unfortunately for me, I prefer my ciders more on the tart side so I probably should be bottling a little earlier to avoid this.
I have never played with salt additions to control pH, so I can’t help you there.
If you boil some juice, or better, apple concentrate, and add with sorbate and sulfite, you should be safe with backsweetening and might even get carbonation. However, in my own experience, results have varied a lot. Over time, I get one of two things: 1) sweet but flat cider, or 2) an extremely dry cider that gushes like champagne. It seems sulfite and sorbate are only partially effective, not complete, unless added in high amounts to where you can taste the salts, and I do not like the taste of these salts. So, most of the time these days, I’m drinking my ciders flat, and do not backsweeten or prime to carbonate.
I love the Cote des Blancs yeast, it is the best I’ve tasted. My fermentations have been anywhere from 40 to 70 F, with similar results. They say that low and slow is the way to go, so I’ll usually keep mine between 40 and 60 F for several months.
Poo on yeast nutrients. Not necessary. Add some for a little insurance, or don’t. They haven’t made a difference in my experience.
One thing I’d like to try next year is Scottish ale yeast. Last year Zymurgy magazine ran a bunch of experiments with beer yeasts in cider, and found that this yeast left the cider tasting more sweet with the most pleasant flavor. So that might be worth a try, in lieu of wine yeast (Cote des Blancs), which will usually take your cider all the way down to 0.992 unless you rack 3 or 4 times during active fermentation, which I think is key to a great cider – rack early and often. Gelatin additions also help greatly when you want to remove yeast during the first few weeks of fermentation to slow things down. Boil a cup of water in the microwave, add a tablespoon of Knox unflavored gelatin, stir to dissolve, cool, and add to your cider. 48 hours later, your cider is clear as crystal, and 95% of the yeast removed. This helps to slow fermentation better than any sorbate or sulfite additions.