# Cold Brew — bench notes (R&D log)

Notebook: Bench 3, immersion rig. All readings on the Hadley-Roe refractometer (cal'd weekly).
Default house bean: Cordwell Roastworks "Slow Tide" medium roast unless noted.

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2026-02-11 — first pass, immersion.
- grind: COARSE. sea-salt-ish, ~1100-1200 micron. burr set 9.5 on the Vossberg.
- ratio: 1:8 concentrate (250 g grounds / 2000 g water).
- water: filtered, 22 C room temp. Total Dissolved Solids (TDS) in ~38 ppm.
- steep: 16 h, lid on, no stir after t=0.
- screen + paper filter on draw-off. slow, ~8 min gravity.
- concentrate TDS: 4.1%. tastes intense, choc/raisin, low acid.
- dilute 1:3 (conc:water) for cupping. final TDS ~1.05%. smooth. way less sour than hot drip.

2026-02-12 — note to self.
- coarse grind matters. fines = silty cup + over-extraction during long steep.
- 12-18 h is the working window. <12 = thin/sour, >18 = woody.

2026-02-14 — temp split test.
- A: room temp 22 C, 14 h.
- B: fridge 4 C, 14 h.
- fridge run reads LOWER conc TDS (3.6% vs 4.0% room). slower extraction cold.
- to match, fridge wants 18 h. room can stop ~14.
- flavor: fridge = cleaner, brighter. room = rounder, heavier body.

2026-02-15 — ratio sanity.
- target brewing strength = ~1:8 grounds:water for the CONCENTRATE.
- then DILUTE to taste. typical serve 1:1 up to 1:3 with water or milk + ice.
- 1:8 is the anchor number. everything dilutes down from there.

2026-02-18 — caffeine, the big one.
- KEY: cold brew often ends up HIGHER total caffeine than hot drip. counterintuitive.
- reason: huge grounds-to-water ratio (~1:8) + the 12-18 h steep. long contact pulls a LOT.
- the "cold = less caffeine" thing is a myth. it's about the concentrate, not the temp.
- caveat: people DILUTE it, so a finished glass varies. but per gram of grounds used,
  cold brew is loaded.
- bench number we're quoting internally: a 1:8 concentrate runs ~2.5x the caffeine of a
  standard hot drip mug, before dilution.

2026-02-19 — half-life note (physiology, for the menu cards).
- caffeine half-life in the body: about 3 hours.
- so a big afternoon cold brew lingers. flag on the "after 2pm" decaf upsell.

2026-02-21 — extraction yield check.
- EY = (TDS% x beverage mass) / dry grounds mass.
- room 14 h run: conc TDS 4.0%, draw-off 1820 g, grounds 250 g.
- EY ~= (0.040 x 1820) / 250 = 29.1%. high but the long steep gets there gently, no bitterness.
- hot drip on same bean lands EY ~20%. cold pulls more total solubles over time.

2026-02-22 — filter notes.
- paper after the screen kills the silt. cup goes glassy clear.
- nylon-only = more body but cloudy + sediment at the bottom of the keg.
- house spec: SS screen draw-off, then single paper polish. don't skip.

2026-02-24 — water redo.
- bumped TDS to 60 ppm (added Brewmaster's mineral sachet).
- conc TDS up a touch, 4.2%. sweeter, more defined. acid still low.
- too soft water (<30 ppm) = flat, hollow. mineral helps.

2026-02-26 — grind regrind.
- tried medium-coarse (burr 8). conc went silty + slightly astringent at 16 h.
- back to 9.5. coarse is non-negotiable for the long steep.

2026-03-01 — batch scale-up.
- 5 kg grounds / 40 kg water = 1:8 again. 18 h room temp (cold kitchen, 19 C).
- conc TDS 4.0%. consistent w/ small batch. good.
- yield off the press ~36 L concentrate.

2026-03-04 — shelf life.
- concentrate, sealed, fridge: good ~10-14 days. acidity creeps up after.
- diluted/ready-to-drink: 2-3 days max. flavor drops fast.

2026-03-06 — milk service.
- 1:1 conc:whole milk over ice = the seller. body carries.
- oat works, almond goes thin. spec oat as default alt.

2026-03-09 — A/B vs nitro tap.
- same conc, charged N2. creamier mouthfeel, perceived sweeter, caffeine unchanged obv.
- TDS identical, ~4.0%. it's texture not extraction.

2026-03-11 — recap card for new staff:
- COARSE grind.
- STEEP 12-18 h (room temp OR fridge — fridge wants the longer end).
- 1:8 concentrate, then DILUTE to taste.
- smoother + less acidic than hot.
- HIGHER total caffeine than hot drip (myth-buster — say it at the bar).
- caffeine half-life ~3 h — don't sell the triple after 3pm.

2026-03-12 — open Qs.
- does a t=8h stir lift EY without silt? test next week.
- map conc TDS vs steep hours, 10/12/14/16/18, single curve.
- decaf cold brew line — same method, confirm low residual.

2026-03-14 — stir test result.
- single gentle stir at t=8 h. conc TDS 4.3% vs 4.0% control. slight bump, no astringency.
- adopt for batch only (small batch not worth the labor).

2026-03-17 — steep curve, room 22 C, 1:8.
- 10 h: 3.1%
- 12 h: 3.5%
- 14 h: 4.0%
- 16 h: 4.1%
- 18 h: 4.2%
- plateau after ~16 h. diminishing returns + woody risk past 18.

2026-03-19 — close-out for the quarter.
- house cold brew SPEC LOCKED:
  - grind coarse (burr 9.5), 1:8, room temp 14-16 h or fridge 18 h.
  - SS screen + paper. mineral water ~60 ppm.
  - conc TDS target 4.0-4.2%. serve diluted 1:2 default.
- remember the two talking points: lower acid, higher caffeine. both true. both sell.
