The bracket is the Henderson–Hasselbalch ratio of bisulfite to molecular SO₂
as a multiplier: about 16 at pH 3.0, 40 at pH 3.4, and 99 at pH 3.8. It
changes sixfold over four tenths of a pH unit, so a dose given without a pH
is meaningless.
Current free SO₂ comes from the brewer
currentFreeSo2MgL is the brewer's own measurement, from an
aeration-oxidation rig, a Ripper titration or a test strip. We don't
estimate it from a previous addition, because free SO₂ binds to
acetaldehyde and anthocyanins at a rate you can't compute from the dose, so
any estimate would be a guess. If it's left out it's zero, which doses the
drink as if it had never been sulfited.
Above pH 3.8, sulfite isn't enough on its own
A cider much over CIDER_SULFITE_PH_CEILING needs more free SO₂ than
is practical or, in some places, legal. Lea's advice is to acidify first and
sulfite afterwards, and the explanation adds a note saying so instead of
just returning a large number.
A drink already holding more free SO₂ than the target needs is dosed at zero,
not at a negative weight.
Potassium metabisulfite for a molecular SO₂ target at a given pH.
The bracket is the Henderson–Hasselbalch ratio of bisulfite to molecular SO₂ as a multiplier: about 16 at pH 3.0, 40 at pH 3.4, and 99 at pH 3.8. It changes sixfold over four tenths of a pH unit, so a dose given without a pH is meaningless.
Current free SO₂ comes from the brewer
currentFreeSo2MgLis the brewer's own measurement, from an aeration-oxidation rig, a Ripper titration or a test strip. We don't estimate it from a previous addition, because free SO₂ binds to acetaldehyde and anthocyanins at a rate you can't compute from the dose, so any estimate would be a guess. If it's left out it's zero, which doses the drink as if it had never been sulfited.Above pH 3.8, sulfite isn't enough on its own
A cider much over CIDER_SULFITE_PH_CEILING needs more free SO₂ than is practical or, in some places, legal. Lea's advice is to acidify first and sulfite afterwards, and the explanation adds a note saying so instead of just returning a large number.
A drink already holding more free SO₂ than the target needs is dosed at zero, not at a negative weight.