Cooking for engineers - Soda bread recipe

Alex Mags
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soda bread!

Here’s the technical specification for a tasty loaf of bread. A restaurant near me serves and sells this bread. It’s very quick to make and so tasty!

The Chemistry Stack Overview

Soda bread is fundamentally a chemical leavening system. Unlike yeast-based breads that rely on biological fermentation (slow deployment), soda bread uses an acid-base reaction for immediate lift. The kefir/buttermilk (pH ~4.5) reacts with sodium bicarbonate (NaHCO₃) to produce carbon dioxide gas, which expands in the dough matrix to create the crumb structure—think of it like deploying a containerized workload that instantly scales your dough volume.

Prerequisites:

  • An oven at 220C
  • Baking tray, roasting tin or loaf tin lined with baking parchment/grease proof paper
  • Mixing bowl
  • Wooden spoon
  • Cooling rack (optional but helps underside of loaf crisp up while cooling)

Dry ingredients:

  • 200g plain flour (~3.75dl)
  • 60g Porridge oats (chopped if they’re jumbo oats)
  • 8g bicarbonate of soda
  • 8g salt
  • 15g soft brown sugar

Wet ingredients:

  • 190g Buttermilk or Kefir (~2dl)
  • 25g Black treacle (~1 heaped tablespoon)

Implementation steps:

Step 1: Oven Preheating (220°C)

Why: Preheating is critical for the Maillard reaction window. When dough hits a hot surface, the exterior proteins and sugars begin cross-linking (browning) at 140-165°C. At 220°C, this happens rapidly before the center has time to fully rise, creating the characteristic crust while the interior expands. Failure to preheat = slow rise = dense crumb.

Scientific detail: The dough must reach ~100°C internal temp within the first 10 minutes to set the crumb structure before CO₂ escapes.

Step 2: Line baking tray with parchment

Why: The parchment creates a moisture barrier, allowing the underside to crisp via Maillard reaction rather than steam-softening. Non-stick compounds on parchment (typically silicone) degrade around 250°C, so 220°C is safely within spec.

Tip mechanics: Wetting one side of parchment increases capillary adhesion to the tray—water molecules bridge the parchment and tray surface, preventing slippage during pouring.

Step 3: Mix dry ingredients

Why: Distributing salt and baking soda evenly prevents pockets of un-reacted sodium bicarbonate. Salt also denatures gluten proteins (breaks apart the long protein chains), tenderizing the crumb. The brown sugar’s hygroscopicity (moisture-absorbing property) helps regulate water distribution in the dough.

Lump crushing: Brown sugar’s hygroscopic nature causes clumping. Crushing breaks apart these compacted sucrose crystals, allowing even dispersal and consistent sweetness + Maillard reaction across the loaf.

Step 4: Combine wet + dry ingredients

The critical reaction begins here:

When buttermilk (lactic acid, pH ~4.5) contacts sodium bicarbonate, the reaction is:

HCO₃⁻ + H⁺ → H₂O + CO₂↑

This is a synchronous reaction—CO₂ is released immediately as a gas. At room temperature, you have perhaps 10-15 minutes before most of the acid is consumed and the reaction rate drops to near-zero. This is why you must bake quickly.

Dough texture note: The resulting sticky dough is intentional. High water content (190g liquid : 200g flour = 95% hydration) creates steam alongside CO₂, producing an open, soft crumb. Lower water would yield dense bread.

Temperature sensitivity: If your kitchen is warm (>22°C), the reaction accelerates. If cold (<15°C), it slows—keep ingredients cool if you’re in a hot climate.

Step 5: Pour dough into prepared tin

Thickness uniformity ensures consistent baking. Thin areas may be over-baked (dry) while thick centers remain gummy. Aim for ~3-4cm depth.

Why “pour” not “knead”? Kneading develops gluten networks (desirable in yeast breads for structure and chewiness). Soda bread relies on the minimal gluten already present plus CO₂ bubbles for structure—over-working develops too much gluten, producing a tough, dense crumb instead of the tender, open structure we want.

Step 6: Dust top with flour

Purpose: This creates a flour seal that prevents excessive CO₂ escape during early baking, improving oven-spring (initial rapid rise). The flour also participates in Maillard browning, creating visual appeal.

Secondary benefit: Signals to visual inspection when the loaf is “done”—golden-brown flour coating indicates ~25 min bake time.

Step 7: Make deep cross-cut

Engineering precision here is critical.

As the loaf bakes:

  • Interior reaches 100°C → CO₂ expands, pressure increases
  • Dough moisture → steam at 100°C, further pressurizing the crumb
  • Without a controlled outlet, the dough splits randomly

The pre-made cut provides a stress relief valve. The dough expands along your cut preferentially (lowest resistance path), creating an attractive cross-hatch. The cut also accelerates interior heat penetration—thinner sections bake faster, preventing a gummy center.

Cut depth: ~0.5cm deep; too shallow won’t guide expansion, too deep may inhibit rise.

Step 8: Bake for 25 minutes at 220°C

Temperature/time relationship:

  • 0-5 min: CO₂ expands + steam generation; dough is still expanding (oven spring)
  • 5-15 min: Maillard reaction dominates; exterior proteins cross-link, crust sets; interior reaches ~90°C
  • 15-25 min: Carryover cooking; interior reaches target ~98°C (just before the crumb sets too firm)

How to verify doneness:

  • Tap bottom of loaf—should sound hollow (indicates moisture has evaporated from exterior)
  • Internal temp ~98°C (use instant-read thermometer)
  • If it’s still dense/gummy when cut, it under-baked; if hard throughout, it over-baked

25 minutes is optimal for a ~400g loaf at 220°C. Scale time proportionally: A smaller loaf might need 20 min; a larger one 28-30 min. Use temp as ground truth, not time.

Step 9: Cool on rack

Why a rack (not a plate): The underside continues baking via radiant heat from below. On a plate, trapped steam softens the bottom crust; a rack allows air circulation underneath, crisp-ing it via dry heat.

Cooling duration: 15-20 minutes minimum. The interior is still set-ting via starch gelatinization. Cutting too early releases steam, collapsing the crumb structure. The Maillard-browned crust is brittle when hot; cooling allows the crumb to firm up and moisture to redistribute, making slicing easier.

Residual carryover: Interior temp continues climbing ~2-3°C for the first 5 minutes off the oven due to thermal lag—another reason to wait before cutting.

Serve with butter or a sharp cheese such as cheddar.

Ingredient Specifications (Chemistry Rationale)

Plain flour (200g): Provides starch (for structure + Maillard browning) and minimal protein (~10-12%). Lower protein than bread flour—you want gluten development to stay low.

Porridge oats (60g): Beta-glucans (soluble fiber) absorb water, tenderizing the crumb. They also add nuttiness via Maillard. The oats are your secondary leavening agent—they trap bubbles better than flour alone.

Sodium bicarbonate (8g): Your acid catalyst. The stoichiometric ratio to lactic acid in buttermilk is roughly 1:1.5 by weight, but 8g is slightly less than needed for complete conversion. This is intentional—excess bicarbonate tastes metallic. Any unreacted buttermilk just adds tang (desirable).

Salt (8g): ~2% by weight of flour. Suppresses gluten development, tenderizes. Also enhances flavor perception—a bit of salt makes the bread taste sweeter.

Brown sugar (15g): Provides sucrose for Maillard (browning), plus molasses (hygroscopic, keeps crumb moist longer). Light vs. dark brown makes minimal difference; use what you have.

Buttermilk/Kefir (190g): The acid source (pH 4.5). Kefir adds probiotics and slight tang. Buttermilk is traditional. Never use milk—no acid means no rise. The 190g creates 95% hydration; essential for a tender crumb.

Black treacle (25g): Adds moisture + deep Maillard flavors. Iron oxide in treacle also makes browning darker. Optional but recommended.

Troubleshooting Matrix

Problem Likely Cause Fix
Dense, gummy center Under-baked (interior didn’t reach 98°C) Increase bake time 2-3 min; lower oven rack closer to heat source
Collapsed loaf post-bake Over-fermented (all acid consumed before crust set) Mix and bake faster; chill ingredients before use
Pale, soft crust Insufficient Maillard (temp or time too low) Increase oven temp to 230°C; bake 27-30 min
Metallic taste Excess unreacted baking soda Reduce NaHCO₃ to 7g next time; ensure buttermilk is fresh (acidity degrades)
Split randomly instead of at cut Cut too shallow or dough over-fermented Deepen cut to 0.75cm; reduce wait time before baking
Dry, crumbly crumb Over-baked or hydration too low Reduce bake time 2 min; increase buttermilk to 200g next batch

Evidence

soda bread with cheese!

References: