Brix, pH and what to measure
Updated
A short list of measurements that between them describe a drink well enough to reproduce it.
Four numbers run this property
Brix, pH, titratable acidity and the ratio between the last two.
Add carbonation and alcohol where the product has them, and that is the whole specification.
Brix
Soluble solids, mostly sugar, read on a refractometer in seconds.
It is the fastest measurement you have and the best process indicator for a fermentation: Brix falling over days is the culture working, and Brix stopping is the ferment finished.
Correct for temperature, and note that a refractometer reading is thrown off by alcohol, so in a fermented product it is a trend rather than an absolute.
Residual Brix at bottling is also the direct predictor of how much further the product can ferment, which makes it the number behind both thresholds.
pH
A calibrated meter, not strips.
Safety at one end, 4.6 and 4.0 are the figures to know, and flavor at the other.
Measure at a standard temperature and record it, because pH reads differently warm.
And calibrate daily on a day you are using it. A drifting meter looks exactly like a drifting product.
Titratable acidity, and the ratio
pH measures acid strength; titratable acidity measures how much acid there is. They are different and both matter.
TA correlates with perceived sourness far better than pH does, which is why two drinks at the same pH can taste nothing alike.
The Brix to acid ratio is a good predictor of whether a drink tastes balanced, and it is the number the juice industry has run on for decades.
Record all four on every batch. It takes five minutes and it is the difference between a product and a series of similar drinks.