Vinegar, titration, its ceiling, and the 5% line
Vinegar-making is fermentation with a delivery deadline: the ethanol must convert, the acidity must reach a strength worth bottling, and both facts have to be measured. The vinegar guide works the whole pipeline in numbers; the pieces worth carrying to the bench are below.
Planning the base, and the ceiling
The planner's rule is volume arithmetic: total volume = wine volume × wine ABV ÷ target ABV, water filling the rest. The calculator's worked default: 750 mL of 12% wine toward a 6% target gives 1,500 mL total, 750 mL of water, and the mother (300 mL, carrying no meaningful ethanol) replaces 300 of those. Then chemistry sets a boundary: the maximum final acidity = starting acidity + 1.029 × the ABV you're converting, ethanol at 0.7893 g/mL converts by moles one-to-one into acetic acid, and the 1.029 factor carries the weight relation. The ceiling is a ceiling: real batches land lower, and the only way to know where yours landed is to titrate it. NC State's range for the starting alcohol is 5.5–7%. The 5% acetic acid NC State lists for preserving and pickling is a separate figure about the finished vinegar, which only a titration tells you. For canning, Penn State Extension says to use commercial 5% vinegar, not homemade.
The titration, the only real read
The site's rule from the wiki applies at full strength here, because pH tells you the direction and titration tells you the amount. The guide's formula: g/100 mL = N × NaOH mL × 6.005 ÷ sample mL. Worked: a 5.0 mL sample, 0.100 N base, 40.0 mL used = 4.80 g/100 mL. A diluted sample works the same through the dilution ratio; a wine-kit reading converted from tartaric multiplies by 0.8002 to land in acetic terms.
The NaOH itself gets its own honesty step: standardize with KHP before you trust a number, 0.5000 g of KHP neutralized by 24.50 mL gives 0.0999 N. Lye solutions age; the app re-reminds you when yours has aged past your own limit.
Strength, and the two lines
Dilution to finishing strength runs on C₁V₁ = C₂V₂: 1,000 mL at 7.4% toward 5.0% wants 1,480 mL total, so add 480 mL of water. Then the two reading-lines from the guide's table: below 5.0% acidity sits under what NC State lists for preserving and pickling, and below 4.0%, the FDA's vinegar standard, the jar cannot even carry the name for sale. The ferment itself runs at NC State's ideal home range of 80–85 °F, with the optional pasteurize step at 140–160 °F held 30 minutes or more for shelf stability.
Titrate the batch, name its base, write the row. Label the batch. — the cellar crew