Claude's paper on 'Acidity and pH of apple juice' is very helpful. The gist is that pH and TA are both helpful but not interchangable. To measure pH use pH test strips. To measure TA use the wine acid test kit. This will measure in % Tartaric (a number like .5875%), which is 5.875 g/l (grams per litre). To convert that to g/l of malic acid, multiply by 0.89. A range of 4.5 (g/l malic) to 7.5 is good, with the low typical of English cider made with bittersweet apples and the high a North American sparkling. Claude mentioned during the '11 Cider Days that he blends shooting for 7 g/l malic. His apple blending pdf says to shoot for a TA of around .6-.8% tartaric, though .5-.9% is ok. A refreshing sparkling Champagne type would be around .8% where a flat European style would be around .55%. See his chart on p.17 of the blending pdf.
Andrew Lea's SO2 by pH chart is on p.67.
Paul says on p.16 "Under normal conditions, the juice of North American apples will have a specific gravity between 1.040 and 1.050. ... This level may not entirely safeguard your cider against unwanted yeast activity even after bottling. Some organisms survive quite well in lower-alcohol ciders, especially if the storage tempatures rise above 60 degrees F ... during the course of the season. ... A delicate, low-alcohol cider may be made, stored, and consumed without hesitation only if kept well chilled or if a preservative, such as Campden tablets, is added prior to bottling (one crushed [50ppm] tablet per gallon). Otherwise, bring the specific gravity up to at least 1.060 ..."
Andrew says on p.59 "As a rule of thumb, if the juice S.G. is less than 1.045 and you have no sweeter juice for blending, it is wise to bring it up to this level by the addition of sugar." Similarly, Proulx & Nichols, p.46, say, "Juice with a specific gravity below 1.045 will yield less than 5.7 percent alcohol and will have risky keeping qualities. It is best to add sugar and bring up the specific gravity to at least 1.045 or 1.047.
CvilleKevin says "Most of the flavor of the cider disappears between 1.005 and 1.000. Once you are at 1.000, you can add sweetness back, but not flavor (unless you are adding juice back, but even then, its not the same flavor). That is why a lot of the commercial sweet ciders have a fairly high sugar level, but not a lot of flavor IMHO. Just about all of the sugars in cider are fermentable, and given enough time, most yeasts will get around to eating all of them. But the yeast does seem to prefer the simpler sugars first. Getting the sugar up to 1.060 or 1.065 also makes the fermentation easier to stop, as the ABV is higher and nutrient levels are lower."
To raise the specific gravity of one gallon of juice 5 degrees, add 2.25 ounces of granulated sugar. Stir cane sugar directly into the cider. For other sugar options and notes see Paul's book, p.36.
Note to self: the Campden tablets you have are Potassium Metabisulfite, aka k-meta.
From CvilleKevin, "I started using k-meta again on about half of my keg batches, to get better longevity. With no k-meta, the ciders taste a lot better in the first three months, but would often get a little too acidic in the 9-18 month range."
From NorthernWiner: "K-meta," as several posters have said, is Potassium Metabisulfite. In brew shops, you usually see it in powdered form. Campden tablets are not the same as K-meta. Campden can contain either Potassium Metabisulfite or Sodium Metabisulfite, but also contains binders and fillers to hold it together. You really need to read the label to know for certain which type of meta you're getting. A lot of people find Campden tablets easier to use than powder, and for small batches of, say, a gallon, it's easier to measure. Sodium metabisulfite is not "bad." It performs the same function as its potassium counterpart, but is slightly stronger. Sodium and potassium metabisulfite powder can be used more or less interchangeably. The commercial wine industry is not allowed to use sodium metabisulfite as an ingredient, and I think that's where its sketchy reputation may have arisen from. If you have a choice between the two, Potassium is preferable, but if all your brew shop carries is Sodium, then go ahead and use it. It won't kill you.
Claude says (paraphrasing his book, loc 5185 or so):
The amount you sulfite depends on the pH and because pH strips are
terrible, uncertainty in 0.2 to 0.3 typically, go with this:
pH between 3.0 and 3.3: addition of 50ppm of SO2
pH between 3.3 and 3.6: addition of 100ppm of SO2
pH between 3.6 adn 3.8: addition of 150ppm of SO2
If you want to do a natural/wild yeast, Claude says use half the above dosage. Soham Bhatt (Artifact Cider Project) suggested just use 25ppm.
My hydrometer gives an accurate reading when the temperature of the liquid is at 60 degrees F. The following tables show how to correct for temperature differences.
| Temp in F | Spec. Gravity Correction |
|---|---|
| 50 | subtract .5 |
| 60 | 0 |
| 70 | add 1 |
| 77 | add 2 |
| Hydrometer table | ||
|---|---|---|
| Specific gravity (S.G.) | Potential %vol alcohol | Grammes sugar / litre |
| 1010 | 0.9 | 12.5 |
| 1015 | 1.6 | 25 |
| 1020 | 2.3 | 44 |
| 1025 | 3.0 | 57 |
| 1030 | 3.7 | 76 |
| 1035 | 4.4 | 95 |
| 1040 | 5.1 | 107 |
| 1045 | 5.8 | 120 |
| 1050 | 6.5 | 132 |
| 1055 | 7.2 | 145 |
| 1060 | 7.8 | 157.5 |
| 1065 | 8.6 | 170 |
| 1070 | 9.2 | 182.5 |
| 1075 | 9.9 | 195 |
| 1080 | 10.6 | 208 |
| 1085 | 11.3 | 225 |
| 1090 | 12.0 | 240 |
| 1095 | 12.7 | 252 |
| 1100 | 13.4 | 265 |
| 1105 | 14.1 | 277 |
| 1110 | 14.9 | 290 |
| 1115 | 15.6 | 302.5 |
| 1120 | 16.3 | 315 |
| 1125 | 17.0 | 327.5 |
| 1130 | 17.7 | 340 |
| 1135 | 18.4 | 352 |