🍞 Ovens, Baking and Heat Transfer

A loaf going into an oven is not simply getting hot. It is passing through a series of separate physical events, each one triggered at its own temperature, and each one either helping you or ruining you depending on when it happens. Learn the ladder and most baking faults stop being mysterious.

Here is the ladder, in the order the loaf climbs it.

1. Gluten denaturation begins at about 50 degrees Celsius.
2. Yeast dies between 50 and 60 degrees. One source puts the terminal death point at 59 degrees, another describes yeast death during baking across 50 to 60 degrees. Treat the band, not a single figure, as the truth.
3. Maximum enzymatic activity is at 60 degrees. That is the last burst of alpha-amylase releasing sugar before it is destroyed.
4. Starch gelatinisation begins at 55 to 65 degrees, with granules swelling in that same band, and the starch gel forms across 60 to 80 degrees.
5. Gluten coagulates at 70 to 80 degrees.
6. Enzymes are inactivated at 70 to 85 degrees.
7. Dough becomes crumb above 85 degrees.
8. Crumb structure finally sets when the core reaches 91 to 93 degrees.

Now look at what that ladder tells you about oven spring, which is the rapid expansion in the first minutes of the bake. Three things drive it: the gas already in the dough expanding as it warms, carbon dioxide coming out of the dough faster as the yeast makes a final push, and alcohol and water turning to vapour. All of that is pushing outwards.

What stops it? The yeast dies at 50 to 60 degrees, so the gas production stops. Then the structure sets as starch gelatinises and gluten coagulates at 70 to 85 degrees. The window between those two points is the whole of oven spring. That is the entire budget of expansion you get, and nothing you do after the loaf enters the oven can extend it.

This explains two faults that otherwise look unrelated. An under-proofed loaf bursts at the sides, because it still had expansion left in it when the crust set, and the expansion had to go somewhere, so it tore through the weakest point. An over-proofed loaf collapses, because its gas cells had already stretched past what they could hold before it ever reached the oven, and they fail rather than expand. Both loaves are wrong for the same reason: the amount of proof did not match the expansion window the oven was about to give them.

Now the most useful physical fact in this whole module. The core of a loaf cannot exceed 100 degrees Celsius at normal atmospheric pressure, because that is the boiling point of water and the crumb is wet. All the energy going in beyond that point goes into turning water into steam, not into raising the temperature. That is why a general baked-good core at the end of the bake sits at 90 to 97 degrees and never higher.

Use that ceiling as a diagnostic. If you probe a loaf and read 88 degrees at the core, it is genuinely below the target for a lean bread, and more time will help. If you probe and read 96 degrees and it still looks and tastes underbaked in the middle, then more oven time will not fix it, because the core is already almost at the ceiling. Your problem is elsewhere: the loaf is too large for the bake time, the dough was too wet, or the crumb never set because the structure failed.

The outside of the loaf plays by different rules entirely, because it dries out and can therefore go far past 100 degrees. Maillard browning starts above 105 degrees and needs the crust surface above roughly 130 degrees. Caramelisation begins at 160 degrees. So inside your loaf you have a wet core stuck below 100 degrees and a dry crust running at 130 to 160 degrees and above, at the same moment, in the same product. Understanding that split is understanding baking. Lesson 3 is about managing it.

One honest limitation. A quantified table saying how long a given loaf takes to climb this ladder was not available for this course, because the sources describe temperatures, not times. Times depend on your loaf size, your dough temperature, your oven and your loading. So you climb the ladder with a probe, not with a clock.

There is no best oven. There is only the oven that fits your product, your volume, your fuel supply and the money you can raise. Work through the tiers honestly before you spend anything.

Tier one is the drum oven or improvised oven, typically a converted oil drum fired with wood. It has the lowest capital cost, the highest fuel use and the poorest temperature control of anything in this list. A specific capital cost for a drum oven was not available for this course, and it varies so widely with local fabrication that a single number would mislead you anyway. Its honest place is as a starting point that earns the money for tier two, not as a permanent installation.

Tier one-b is the improved wood-fired stove or oven. The Mirt stove in Ethiopia is published at an indicative USD 11 for a single unit and USD 126 for a clustered four-unit installation, and it delivers a 50 percent fuel reduction against an open fire. Those are the published figures for one design in one country and must be verified locally before you plan around them.

Tier two is the improved or rocket baking oven. Ugandan rocket ovens are published at an indicative USD 1,616 to USD 7,474, with capacities running from 12 to 24 loaves for the small units up to 760 loaves for the large ones. The reported gains are substantial: preheat time cut by at least two thirds, firewood use falling to one tenth of what the previous oven consumed, and an efficiency increase of 70 percent. Improved ovens in general are published as delivering fuel reductions of 50 to 80 percent against traditional ovens. Baking in these improved wood-fired ovens is done at around 250 degrees Celsius.

Tier three is the electric deck oven, published for a two to three deck unit at an indicative R9,000 to R30,000, and the gas deck oven at an indicative R25,000 to R55,000. Those figures are South African rand from a single commercial guide dated June 2026 and are shown only so you can see the shape of the gap between tiers. In your own market, import duty, VAT and freight will often dominate the delivered cost, and a locally fabricated or second-hand unit can differ from a new import by an order of magnitude.

Tier four is the commercial rotary or reel oven, published at an indicative R200,000 to R380,000. This is full commercial scale and is not a first purchase.

Now what each one suits. A wood-fired oven with poor control and a long cooling curve suits bread and other products that tolerate a falling temperature and a variable deck. It punishes anything needing precision, which means cakes and delicate pastry are difficult in it. A deck oven suits a mixed product range because you can hold a setting and repeat it, and separate decks let you run two temperatures. Gas gives faster response than wood and generally lower running cost than electricity, but it brings a gas installation certificate and a fire compliance requirement in most jurisdictions, which is a licensing question covered in Module 8. Electric is the easiest to control and the most dependent on a supply that many African bakeries do not reliably have. If your power fails three afternoons a week, an electric oven is not cheap at any price, because a bakery that cannot bake still pays its rent.

Here is the single most valuable thing in this lesson, and it costs almost nothing. Oven temperature at the setting dial and oven temperature at the deck are rarely the same thing in a small bakery. Buy an oven thermometer, put it where the product actually sits, and find out. Then map the oven: front, back, left and right. Almost every small oven has a hot corner and a cold corner, and the loaves in the cold corner will be pale and under-volume every single day until you find it and start rotating.

Work the decision. A baker in Gulu, Uganda, currently uses a traditional wood oven and bakes about 200 loaves a day. She is quoted an indicative USD 2,000 for a small rocket oven. The published Habesha Tikus case in Ethiopia records annual fuel cost falling from USD 1,900 to USD 970, a saving of USD 930 a year, income rising by USD 730 a year, and a payback of about 15 months.

1. She cannot use that case as her own figures, because her wood price, her volume and her oven are different.
2. What she can do is copy the method: weigh her wood for one week, price it, and apply the published 50 to 80 percent improved-oven fuel reduction as a range, not a promise.
3. If she burns wood worth USD 40 a week, a 50 percent reduction saves USD 20 a week, or about USD 1,040 a year, and USD 2,000 of capital pays back in roughly two years at the pessimistic end of the range.
4. That calculation, done with her own wood price, is worth more than any brochure.

Buy the oven that your fuel supply and your product mix justify, and buy a probe thermometer regardless of tier. It is the cheapest quality-control instrument in the bakery, and Lessons 1, 4 and 6 are all unusable without it.

Crust is the part of the loaf your customer sees first and judges the bakery by. It is also the part most often blamed on the oven when the cause is in the flour or in the proof.

Start with the physics from Lesson 1. The inside of a loaf is wet and cannot pass 100 degrees Celsius. The outside dries out, and once it is dry it can climb far past that. Crust is simply the part of the loaf that has dried enough to exceed 100 degrees and then go on rising. Everything about crust management is about controlling when that drying happens and how far the surface goes afterwards.

Now the browning drivers, with their temperatures.

1. Maillard browning begins above 105 degrees Celsius, and needs a crust surface exceeding roughly 130 degrees to run properly. It is the reaction between sugars and proteins and it produces most of bread's colour and much of its aroma.
2. Caramelisation begins at 160 degrees Celsius. This is sugar breaking down under heat on its own.
3. Lactose from milk powder caramelises and gives a darker crust, which is why an enriched dough colours faster than a lean one at the same setting.

That is why a surface that stays wet does not brown. Water sitting on the crust holds the surface near 100 degrees, well below the 130 degrees Maillard needs. A moist surface early in the bake therefore delays crust formation, and delaying crust formation keeps the loaf flexible for longer during the oven spring window described in Lesson 1. That, in mechanism, is what steam in a bread oven is for: it keeps the surface pliable while the loaf is still expanding, and it only browns once the surface finally dries.

Be careful here, because this course must be honest with you about what it does not know. Published figures for how much steam to inject, for how long, and at what point in the bake, were not available for this course. Nothing in this lesson gives you a steam quantity or a steam duration, and you should treat any number you are given elsewhere with the same scepticism you would apply to any unsourced figure. What you can do is test it in your own oven: bake two identical loaves, one with a surface misted or with a pan of water in the oven at loading and one without, and record what each crust looks like. That comparison, written down, is your own data and it is better than a borrowed number.

Now the diagnosis, which is where the money is. Pale crust is the fault most often misdiagnosed as a broken oven. Work the list in this order before you touch the thermostat.

1. Is the bake long enough? Underbaking is the first listed cause of a pale crust.
2. Is there enough residual sugar left after fermentation? Sugar drives both caramelisation and Maillard browning. A bread dough needs 3 to 3.5 percent fermentable solids just for yeast activity, and if the formula is short of sugar there is nothing left to brown.
3. Is the dough over-proofed? Over-proofing is a listed cause of pale crust colour, because the yeast has consumed the sugar that would have coloured the loaf. Over-proofing also brings coarse grain, poor texture and an acid overtone in the flavour, so look for those alongside.
4. Is the flour's Falling Number too high? Above 300 seconds means minimal enzyme activity, which gives long proof times, pale crust, low volume and dense crumb.
5. Are the pans positioned too closely, or greased too heavily? Both are listed causes.
6. Only after all of that should you suspect the oven.

Over-dark crust runs the same way. Listed causes are old dough, a cool oven and underbaking, which sounds contradictory until you realise a cool oven means a longer bake and more time for the surface to darken. Add to that a Falling Number below 220 seconds, where sprouted grain has released so much sugar that the crust caramelises excessively, and too much sugar in the formula, which is also a listed cause of a loaf bursting on the side.

Crust too thick has its own list: dough too stiff, young dough, underproofing and improper panning.

Work an example. A baker in Kumasi, Ghana, has pale loaves that started three weeks ago. Nothing in his oven changed. His formula carries 4 percent sugar, well above the 3 to 3.5 percent minimum. His proof time is unchanged at his usual schedule but the loaves are noticeably larger before baking than they used to be.

1. Sugar is adequate, so cause two is eliminated.
2. Larger loaves before baking at an unchanged clock time means the dough is fermenting faster, so it is over-proofed by the time it reaches the oven. That fits both the pale crust and the coarse crumb he also reports.
3. Why is it fermenting faster? The bakery is hotter this month, so his dough temperature has risen. That sends him straight to the dough temperature control lesson, not to the oven.
4. The fix is to lower the dough temperature or shorten the proof, and it costs nothing.

The oven was never the problem. That is the pattern, and once you learn it you stop replacing equipment to solve process faults.

This lesson contains the single most reliable test in baking and the single biggest gap in the reference behind this course. Take both seriously.

Start with the gap, because you deserve to know it. A product-by-product oven temperature and time table for bread, rolls, buns, cakes and scones was not available for this course. The general published band across baking processes is an oven set between 150 and 300 degrees Celsius with bakes of 5 to 25 minutes, but the source that gives that band explicitly does not break it down by product, so it is close to useless as an instruction. Only a few product-specific figures were retrieved, and they are these: chocolate chip cookies at 350 degrees Fahrenheit, which is 177 degrees Celsius, for 13 to 15 minutes to a golden bottom; short crust pastry at 177 degrees Celsius for 10 to 15 minutes; choux paste at 370 degrees Fahrenheit, which is 190 degrees Celsius, for about 35 minutes until well puffed and golden; and improved wood-fired African ovens operating at around 250 degrees Celsius.

That is all. Anyone who hands you a confident full table has either sourced it from a text they can name or invented it. So build your own, which is better anyway, because your oven is not their oven and your dial is not your deck.

Now the reliable test. Internal temperature at the core, measured with a probe, tells you doneness regardless of oven, loaf size or altitude. The published bands are these.

1. Lean-dough bread such as baguette, sourdough and rye: 190 to 210 degrees Fahrenheit, or 88 to 99 degrees Celsius.
2. Rich-dough bread such as brioche, dinner rolls, challah and sandwich bread: 180 to 190 Fahrenheit, or 82 to 88 Celsius.
3. Quick breads, muffins, cornbread, biscuits in the American sense, and scones: 200 to 205 Fahrenheit, or 93 to 96 Celsius.
4. Cakes, cupcakes and angel food: 200 to 209 Fahrenheit, or 93 to 98 Celsius.
5. Pound cake: 210 Fahrenheit, or 99 Celsius.
6. Chocolate chip cookies: 180 Fahrenheit, or 82 Celsius.
7. Custards such as creme brulee, flan and pumpkin pie: 170 to 175 Fahrenheit, or 77 to 79 Celsius.
8. Bread pudding, quiche and meringue pies: 160 Fahrenheit, or 71 Celsius.
9. Cheesecake: 150 Fahrenheit, or 66 Celsius.

Notice that rich doughs finish lower than lean doughs. That is not an error. Fat, sugar and egg change how the structure sets, and a brioche taken to 99 degrees is a dry brioche.

A serious warning on the last three lines. The custard, quiche and bread pudding temperatures are quality temperatures. They are also food-safety temperatures, because those products contain egg. Your national food code may set a higher mandatory cook temperature for egg-containing products than the quality figure above, and this course does not know what your country requires. Ask your national food safety authority before you sell any egg-set product, and treat this as a licensing question, not a taste question.

Here is how you build your own table in one afternoon. Take the product you make most. Set the oven to the deck temperature you measured in Lesson 2. Load it as you normally load it. Then probe one unit every three minutes from the point you would first consider it done, writing the time and the core temperature each time. When the core enters the published band for that product class, note the clock time. That is your bake time for that product, in that oven, at that loading, at that unit weight. Write it on a card and pin it to the oven. Change any one of those four variables and you repeat the test.

Loading matters more than most bakers think. A full oven and a half-full oven do not bake the same, because the mass of cold product pulls the deck temperature down and it takes time to recover. Pans positioned too closely is a listed cause of pale crust. Rotate through the hot and cold spots you mapped in Lesson 2.

The bake is not finished when the oven is finished. Cooling and wrapping are part of the process and they are where keeping quality is won or lost.

1. Do not slice bread above 95 degrees Fahrenheit, which is 35 degrees Celsius. It caves in. Dull slicer blades and wrong guide settings do the same thing, so check those before blaming the bread.
2. Do not wrap above 95 Fahrenheit or 35 Celsius either. Wrapping warm bread condenses moisture inside the bag and gives poor flavour and poor keeping quality. It is also a mould incubator.
3. Typical cooling to that point takes 2 to 3 hours.
4. Do not stack loaves during cooling. Stacking traps moisture and warmth, and that favours both rope and mould.

Work the arithmetic on that last point. A baker in Lusaka, Zambia, finishes baking at 14:00 and his delivery van leaves at 15:30. He wraps at 15:15 because the van will not wait. Cooling takes 2 to 3 hours, so at 15:15 his loaves are only 75 minutes out of the oven and are certainly above 35 degrees. Every bag he sends out has condensation forming inside it. His customers report mould at day three and he blames his flour. The fix is not a preservative. The fix is to finish baking by 12:30 so the loaves have their three hours, which costs him nothing but a change to the shift start.

Most small bakers know what their flour costs and have no idea what their fuel costs per loaf. That is strange, because fuel is often the second largest variable cost and it is the one an oven change can cut in half.

The method is one line.

Energy cost per unit equals fuel quantity consumed per bake, multiplied by fuel price per unit quantity, divided by units produced per bake.

Everything else is measurement. Take each fuel in turn.

Wood. The published figure for a traditional wood oven is more than 0.5 to 1 kg of wood per kilogram of baked wheat flour. That is a sourced ratio you can start from and then replace with your own measurement. Work it. A baker in Kasese, Uganda, bakes with 10 kg of flour per bake, which by the scaling arithmetic from the baker's percentage module gives about 18 kg of dough and 20 loaves at 900 g each.

1. Wood consumed: 10 kg of flour at 0.5 to 1 kg wood per kg flour gives 5 to 10 kg of wood per bake.
2. Suppose his delivered wood price is an indicative USD 0.10 per kg. He must use his own figure, because this one is illustrative only.
3. Fuel cost per bake equals 5 to 10 kg times USD 0.10, so USD 0.50 to USD 1.00.
4. Energy cost per loaf equals USD 0.50 to 1.00 divided by 20 loaves, so USD 0.025 to USD 0.05 per loaf.
5. Over 200 loaves a day and 26 days a month, that is 5,200 loaves, and at the pessimistic end USD 260 a month in wood.

That last number is the one that justifies an oven upgrade or does not. Now test the upgrade against the published gains. Improved ovens in general are published as reducing fuel by 50 to 80 percent. An improved oven case in Peru is published as using about 3 kg of firewood per 90 minutes, roughly 10 kilowatts thermal equivalent, and a 50 percent fuel reduction. Ugandan rocket ovens are published as cutting preheat time by at least two thirds, dropping firewood to one tenth of previous use, and raising efficiency by 70 percent, with a fuel cost figure of USD 234 per cubic metre. The Mirt stove in Ethiopia is published at a 50 percent reduction against an open fire.

1. Apply the conservative half of the published band to the Kasese baker: a 50 percent reduction on USD 260 a month saves USD 130 a month, or USD 1,560 a year.
2. Against an indicative rocket oven capital cost of USD 1,616 to USD 7,474, the small end pays back in about 12 to 13 months on fuel alone.
3. The published Habesha Tikus case in Ethiopia gives the same shape: annual fuel cost falling from USD 1,900 to USD 970, a saving of USD 930, income rising USD 730, and payback in about 15 months.
4. Do not adopt those figures. Redo every line with your own wood price and your own loaf count, because that is what a lender will ask for anyway.

Gas. Published consumption figures for gas deck ovens were not available for this course, and this course will not invent one. Measure instead, and it is easy: weigh the cylinder before the day's baking and after, and the difference is your consumption in kilograms. Divide the cylinder refill price by the cylinder's kilogram capacity to get your price per kilogram, multiply, and divide by units produced. One day's measurement gives you a figure that no brochure can.

Electricity. Published consumption figures for electric deck and rotary ovens were also not available for this course, but you do not need them, because the number is written on the machine. Read the nameplate rating in kilowatts, multiply by the hours of use, and multiply by your local tariff per kilowatt hour. If your nameplate reads a certain kilowatt figure, use that figure and not one from this course, because oven ratings differ enormously. To show only the shape of the arithmetic, suppose a nameplate reads 6 kW and you run it three hours: that is 18 kilowatt hours, and at your own tariff per kilowatt hour you have your cost per bake. Divide by units produced. Note that an oven does not draw its full rating continuously once it is up to temperature, so the nameplate calculation is an upper bound, and a meter reading across one baking day is the more accurate figure if you can take one.

Three things that quietly waste fuel in every small bakery, and cost nothing to fix.

1. Preheating for far longer than needed. Time how long your oven actually takes to reach your deck temperature and preheat for that long, not for a habit.
2. Baking a half-empty oven. The fuel is nearly the same whether the deck is full or half full, so a half-full bake roughly doubles your energy cost per loaf. Consolidating two half bakes into one full bake is free money.
3. Opening the door. Every opening dumps heat you paid for and the oven must recover it.

Put the energy figure into your cost sheet as its own line, alongside ingredients, packaging, labour and overhead. A cost per loaf that omits fuel is not a cost per loaf.

Every fault list you will ever read gives possible causes, not single causes. That is not a weakness of the list, it is the nature of baking, and it means diagnosis is elimination, not lookup. Work through the possibilities in order, changing one variable at a time, and write down what you changed and what happened.

Volume and crumb faults first.

Lack of volume has a long list of possible causes: insufficient yeast, old dough, insufficient intermediate proof, underproofing, improper mixing, oven temperature too high or too low, rough handling, wrong dough temperature, wrong dough consistency, poor yeast quality, wrong pan temperature, wrong proofer conditions, overproofing, improper moulding, dough too sticky or too stiff, a dirty moulder, and improper moulder feeding. Add to that a Falling Number above 300 seconds, which gives low volume and dense crumb through lack of enzyme activity. Note that both underproofing and overproofing appear on the same list. Underproofing also brings shell tops, inadequate flow and bursting at the sides.

Dense crumb comes from insufficient proofing, because the dough never relaxed enough, or from a high Falling Number with insufficient enzyme activity, which gives a long proof, pale crust, low volume and dense crumb together.

Holes in the bread and a coarse open crumb share most of the lack-of-volume list, and add two causes bakers rarely suspect: excess dusting flour and excess divider oil. Both get folded into the dough and both create voids. Also add a Falling Number below 220 seconds, which gives large open holes with a sticky crumb.

Too much volume is a real fault and has four listed causes: a cool oven, insufficient proofer moisture, overbaking, and underscaling. That last one matters commercially, because underscaling means you put less dough in the pan than you should have and the customer is getting a lighter loaf.

Now collapse and shape faults.

Bread caves in from underbaking, from bread being too warm for slicing at above 35 degrees Celsius, from dull slicer blades, and from improper guide settings. Notice that three of those four are not baking faults at all, they are cooling and slicing faults.

Hollow bottom comes from overproofing, a cool oven, improper moulding, or overscaling.

A poorly shaped loaf comes from overmixing, very soft dough, excessive proofer humidity, or young dough. A flat top with sharp corners comes from overmixing, improper moulding, underproofing, or an oven that is too hot.

A loaf bursting on the side comes from an oven that is too hot, overbaking, or too much sugar. Excess shredding or capping comes from improper moulding, improper panning, rough handling, overscaling, or overproofing. Irregular slices and blisters on the crust come from young dough, improper mixing, excessive proofer humidity, rough handling, improper moulding, or very soft dough.

A note on the loaf that collapses in the oven. The troubleshooting source used for this course does not use that exact term. Its nearest entries are bread caves in, which is a post-bake slicing and cooling failure, and hollow bottom, which is an over-proof and moulding failure. The mechanism for a loaf falling during the bake is the over-proof case, where the gas cells over-expanded and failed before the structure set at 70 to 85 degrees. That mechanism is derived from the oven-stage temperatures rather than quoted directly, so treat it as a good explanation rather than a sourced statement.

Crust faults were covered in Lesson 3 and belong in the same log. Crust too pale: underbaking, pans positioned too closely, excessive pan greasing, old dough, overproofing, insufficient residual sugar, or a high Falling Number. Crust too dark: old dough, a cool oven, underbaking, or a low Falling Number. Crust too thick: dough too stiff, young dough, underproofing, or improper panning.

Keeping faults close the list. Poor keeping quality comes from old dough, improper mixing, a high dough temperature against the optimum of 24 to 28 degrees Celsius, underscaling, an improper shortening amount, a proofer that is too hot, a cool oven, overbaking, and an improper wrapping temperature, where wrapping must be at or below 35 degrees after 2 to 3 hours of cooling. Poor flavour shares most of those causes and adds unsanitary equipment contact, contaminated wrappers, mouldy racks and tools, dust exposure, and stale or mouldy product left in circulation.

Here is how to actually use all of this. Keep a fault log with five columns: date, product, fault observed, what you changed, and what happened next. One line per bad batch.

Work the discipline. A baker in Ndola, Zambia, has loaves with holes. He reads the list and sees seventeen possible causes. He does not change seventeen things.

1. He looks at what changed recently. He started using more dusting flour last week because the dough was sticking.
2. Excess dusting flour is on the list, so he tests that first, halving the dusting flour on one trolley and keeping the rest as it was.
3. The trolley with less dusting flour comes out with fewer holes. He has a probable cause after one bake, at no cost.
4. He then asks why the dough was sticking, which takes him back to Falling Number and dough hydration, and he telephones his miller.
5. He writes all five lines in the log.

One variable at a time, written down. That is the whole method, and it beats guessing every time.