Extraction and brewing
Updated
Where a tea, coffee or botanical base is actually made, and where three variables decide everything.
Time, temperature, ratio
How long, how hot, and how much solid to how much water.
Change any one and the result changes. Fix all three and the base is reproducible, which is the entire point.
Write them on the batch sheet as numbers, not as "steep until it looks right".
Hot extraction
Fast, efficient, and it pulls tannins and bitterness along with everything else.
Hotter and longer is not better: past a point you are extracting the compounds that make a drink astringent rather than flavorsome.
It also pasteurizes the base as a side effect, which is a real microbial advantage in an unpasteurized product and is worth knowing you are getting.
Cool it promptly afterwards. A warm base held for hours is the point at which a clean process becomes a contaminated one.
Cold extraction
Slow, smoother, lower in bitterness, and increasingly what the market wants for coffee and tea.
It has a microbial cost that people underrate: nothing is being heated, the material is wet and warm-ish for many hours, and the finished base has had no kill step at all.
So a cold-brewed base needs clean inputs, cold conditions during extraction, and a downstream hurdle, acid, refrigeration or a treatment, rather than relying on the extraction itself.
Getting it repeatable
Weigh the solids, measure the water, time the steep and control the temperature.
Then measure the result: Brix for a sugared base, a refractometer figure for coffee, and taste against a reference.
And record the lot of the tea or coffee, because agricultural material varies between lots more than any process step you control.