French Toast, The Custard Test

This is not a recipe. It’s a four-arm experiment, and it’s the best idea in my whole French toast project. Whole milk, evaporated (PET) milk, cream, and — the arm that actually answers the question — evaporated milk diluted 1:1 with water. Nobody has published a controlled test of this. Every prediction below is a prediction, and I’d like to be wrong about at least one.

Ingredients

• The constants — one variable, everything else held
• 8 slices of the same bread, cut ¾–1 inch thick — same loaf, same thickness
• Weigh your eggs. Hold the egg constant in GRAMS, not in count — eggs vary 15%+ by size
• 8 large eggs, weighed (about 400 g total; 2 eggs / ~100 g per arm)
• Butter for the pan — same fat, same amount, every arm
• Arm 1 — whole milk (the baseline)
• 160 ml whole milk
• Arm 2 — evaporated (PET) milk
• 160 ml evaporated milk
• Arm 3 — heavy cream
• 160 ml heavy cream
• ⭐ Arm 4 — evaporated milk diluted 1:1 with water. THIS IS THE ARM THAT ANSWERS THE QUESTION.
• 80 ml evaporated milk + 80 ml water
• The ratio is 1 egg : 80 ml dairy throughout. Two eggs, 160 ml, two slices, per arm.
• The instruments — not optional
• A scale
• An instant-read probe

Directions

Key ingredients

Evaporated Milk

1. Dry the bread. 275°F / 135°C for 10–15 minutes, flipping once, single layer on a wire rack over a sheet pan. The morning you cook — NOT overnight. The rack matters: it lets moisture escape from the underside instead of steaming against the pan.
2. Target: dry and firm to the touch, but NO colour. Colour means you’ve started Maillard on the surface, which both hardens the crust against absorption and gives you a head start toward burning in the pan. Cool before soaking — a warm slice will cook the custard on contact.
3. (If you want to be rigorous: weigh the slices before and after drying and treat the water-loss percentage as your variable. Nobody publishes an optimal number — NOT FOUND. That’s a genuinely open question you could answer.)
4. Weigh each dried slice and write the number down.
5. Mix each arm’s custard: 2 weighed eggs to 160 ml of that arm’s dairy. Nothing else varies — same spice, same sugar, same salt, or none at all in all four.
6. Same soak time for every arm. Then weigh each slice again. Absorption is now a measured number, not an impression. This is the cheapest instrumentation in the whole experiment.
7. ⚠ COOK TO 180°F INTERNAL. NOT TO COLOUR, NOT TO A TIMER. Probe the centre of the slice and pull each one when it hits temp. Read the notes — this is the single biggest way this experiment could produce a garbage result.
8. Expect the evaporated arm to want a lower pan temperature for longer. That’s fine — you’re controlling for doneness, not for time.
9. Then compare colour and flavour, with each arm at the same interior doneness.
10. Taste blind if you can get someone to hand them to you unlabelled. Evaporated milk’s colour will give it away visually, which will bias you.

Notes

⚠ EVERY PREDICTION BELOW IS A PREDICTION

No controlled side-by-side of whole milk vs evaporated vs cream in French toast custard exists from any source I’d trust. NOT FOUND. What follows is well-established composition and chemistry, and predictions that fall out of it — labelled, so that when the results come in you can tell which reasoning was wrong.

⚠ THE DESIGN WARNING THAT SAVES THE EXPERIMENT

Cook to interior temperature (~180°F), not to colour.

If you cook to colour, the fastest-browning sample looks “done” first and you’ve measured nothing but browning rate — which you already predicted. You’d have run the whole experiment and learned nothing you didn’t start with. Faster browning is not automatically better: against a fixed interior-set requirement of ~180°F, you may hit the colour you want before the custard sets.

The composition table — everything falls out of this

Approximate, per 100 g:

	Water	Fat	Protein	Lactose
Whole milk	~88%	~3.3%	~3.3%	~4.8%
Evaporated milk	~74%	~7.6%	~6.8%	~10%
Heavy cream	~58%	~36%	~2.1%	~2.9%

Note especially: evaporated is roughly 2× concentrated across the board; cream has LESS protein and LESS sugar than plain milk — butterfat has displaced the aqueous phase.

Evaporated milk is Maillard-browned before you open the can — and that’s ESTABLISHED, not a hunch

Evaporated milk is sterilized in the can at 110–120°C for 15–20 minutes. The literature is unambiguous about what that does: it is “light brown in color because of chemical reactions between the protein and the lactose (Maillard reaction) occurring during intensive heat treatment” and “possesses a slight cooked flavor.” That cooked, faintly caramel note you taste straight from the can is literally Maillard product.

And it leaves measurable fingerprints: HMF (hydroxymethylfurfural), lactulose, and furosine — the standard analytical markers used to distinguish in-container-sterilized milk from UHT and pasteurized. In-container sterilization produces far greater Maillard browning than UHT. Evaporated milk is the most heat-abused dairy in the store, by design. The chemistry is documented, not folkloric.

PREDICTION — it browns fastest, for four stacked reasons: 2× the lactose (Maillard fuel); 2× the protein (the other reactant — so it compounds rather than adds); the reaction is already partway down the cascade (your pan isn’t starting it, it’s resuming one in progress); and less water, so the surface dries sooner and browning starts sooner.

Cream: the fat genuinely inhibits the set

Three things happen and two of them fight the set:

1. Less protein per volume (~2.1% vs ~3.3%). Counterintuitive, but it’s the table — butterfat displaced it.
2. Fat physically interrupts the protein network. Coagulation is protein cross-linking into a continuous 3D mesh; dispersed fat globules are inclusions — they occupy volume without contributing bonds. This is why crème brûlée is softer than a milk custard at the same egg loading.
3. But much less water (~58%) pushes the other way, partially offsetting 1 and 2.

PREDICTION: cream sets softest — luxurious, tender, borderline underset, and it will read as undercooked even when it isn’t. If you go cream, add a yolk — more protein and emulsifier, aimed at exactly the deficit cream creates.

⭐ The fourth arm, and why it’s the whole point

The straight three-way comparison confounds two explanations: is evaporated milk different because it’s concentrated, or because it’s pre-cooked?

Evaporated diluted 1:1 with water is back to roughly milk’s concentration but still carrying every Maillard product from the can.

That arm separates concentration from pre-cooked chemistry. It’s the arm that answers the question.

The prediction table — ⚠ ALL PREDICTIONS, NOT TESTED

	Browns fastest	Sets firmest	Soaks deepest	Predicted character
Evaporated	1st (2× lactose, 2× protein, reaction pre-started, less water)	1st (most total protein)	3rd (viscous, least free water per unit solids)	Caramelly, “cooked,” dulce-de-leche notes, firm
Whole milk	2nd	2nd	1st (most water, least viscous)	The baseline. Clean, balanced, custardy
Cream	3rd (least lactose AND least protein)	3rd (fat interrupts the network)	3rd–tied (viscous, water-poor)	Rich, tender, borderline soft; may read underset

⚠ Why oven-dried, not stale — the popular explanation is wrong

Staling is not drying out. Staling is starch retrogradation. Amylose and amylopectin recrystallize; water isn’t lost, it migrates out of the starch granules into the crumb’s air pockets.

The proof: bread stales FASTER in the refrigerator than at room temperature — retrogradation peaks just above freezing, right in the fridge’s ~4°C range. If staling were drying, a humid sealed fridge would preserve bread. It does the opposite. The drying theory is disproved by your own refrigerator. (Also: you can partially un-stale bread by reheating it to ~140°F+. You cannot un-dry it.)

So the two goals come apart:

• Drying = net water leaves the slice → real absorption capacity. This is what you want.
• Staling = water rearranges internally, total moisture roughly constant → firmness, but no absorption capacity, and a real flavour penalty (retrograded starch tastes flat and cardboardy).

Leaving slices out overnight gives you some drying and a lot of staling — you pay the full flavour cost for a fraction of the benefit. Oven-drying removes water fast, at a temperature above the retrogradation range, and heat actually reverses retrogradation while it dries. It’s not a shortcut for the impatient. It’s the strictly superior method.

⚠ Sourcing flags

The 1 egg : 80 ml ratio is reported for Serious Eats/Gritzer (3 eggs : 1 cup) secondhand — the site blocks automated access entirely, so I could not read the primary. Cook’s Illustrated’s exact ratio is paywalled → NOT FOUND, and I’m not guessing at it. The oven-dry temp/time is likewise secondhand (250°F/10 min and 275°F/10 min both get reported).

Read the gap in the ratio, it’s informative: French toast custard at 1 egg : 80 ml is about three times as egg-rich as a pourable dessert custard (1 egg : 240 ml). That’s deliberate — it has to set fast, in a pan, inside a slice, and hold it together. Wet in the middle? More egg, less dairy. Rubbery and omelette-y? Too much egg. 1:80 is the centre; move in 10 ml steps.

The loaf this is built for: Bread, Cinnamon Sourdough Pullman. The syrup: Syrup, Brown Sugar Cinnamon (Jeff’s).