We have done two lots of apple pressing recently. One about 6 weeks ago and another 4 weeks ago. On each occasion we got 5 gallons of juice. So far it has not fermented at all. I used sodium metasulphite to rinse everything out and was fairly liberal with it, but not stupidly so. Otherwise we have added pectinase and yeast nutrient to both barrels. The SG has not budged in this time and the juice (on Sunday last) tasted of apple juice. I have used 6 packs of good champagne/cider yeast with one batch and four with the other (three different sorts of champagne/cider yeast) and I have stirred and agitated (I racked off into another barrel and back again to get as much O2 in as possible). The sulphite strips suggest there is about 10 mg/l remaining so, theoretically, this should not inhibit fermentation. The back kitchen is warm enough. The yeast has been sprinkled on the top several times and on some occasions has been encouraged to begin its fermentation by leaving it to stand in warm water with a bit of sugar added (I make bread, so understand yeast). I have given the yeast about a week to work on each occasion but to no avail. Anyone any other ideas as to what I can do to encourage 10 gallons of apple juice to ferment? We did not have this difficulty last year (our first year when we had a 'vintage' brew) so we are stumped.
I would say it's the Sodium Metasulphite, inhibiting yeast growth.
You need a lot of pure oxygen to defeat that oxygen absorber.
In one experience it took 4 liters of pure oxygen through a .5 micron stone on a stir plate. For 1 gallon of white grape juice that used a metabisulfide as a preservative.
Or you can do a full pitch of yeast and skip the growth phase the yeast won't need oxygen so the preservative has no effect.
For a good fermentation you need several things: sugar, yeast nutrients, oxygen, healthy yeast, and the right temperature. Sugar should be fine, given the fact that it's almost impossible not to have any in your case! Yeast nutrient you have added. That leaves oxygen, yeast health and temperature. Oxygenate (or at least aerate) your must and see if that helps. Proof your yeast by dissolving a teaspoon of sugar in about 1/4 cup of luke-warm water, adding a packet of yeast and letting it stand for about 15 minutes. You should see some activity in the form of foam floating on top. If there's none, your yeast is dead. I'm assuming your must is in the temperature range required by the yeast as specified on the package.
If you had been working from commercially produced apple juice, my concern would be a preservative (pimaricin, potassium sorbate, etc.) specifically aimed at killing fungi (molds but also yeast). But apple juice from your own pressings would be free of all that. (Right?)
Also note that not all fermentations are readily apparent to the naked eye (or tongue). A hydrometer is the weapon of choice when it comes to finding out what is really going on. Take a gravity reading, write down the number, and take another one 48 hours after. If the second reading is exactly like the first one, no fermentation takes place. If it is slightly lower (on the order of 1 to 4 gravity points or so) you have a very slow fermentation on your hands (also not good). If it is significantly lower, you've got a proper fermentation.
So in summary, ensure you've got enough sugar, live (and healthy!) yeast, nutrients and oxygen in the mix at the right temperature, and you should get a fermentation. If you don't get any, these are pretty much the only possible causes.