What your result means
Peak volume is the most foam these whites can hold, and expansion is that as a multiple of the liquid you started with — a clean set of whites reaches about eight times, sugar pulls it down, fat pulls it down hard.
To stiff peaks is the whipping time to the stage where a lifted whisk leaves a point that does not flop. Holds for is how long the foam stays up before water starts draining out of the bubble walls and pooling underneath — the number that decides whether you can leave a bowl standing while the oven heats.
Why this one is different
Peak volume is given as an expansion factor as well as a volume, since that is the figure a recipe implicitly assumes. Time to stiff peaks and how long the foam holds afterwards are reported separately, which is the difference between a meringue that survives folding and one that weeps in the tin.
How it works
Whisking does two jobs at once. It drags air in as large bubbles, then keeps shearing those bubbles into smaller and smaller ones — which is why foam turns from translucent and slack to white and firm without gaining much air. Meanwhile the proteins in the white, which normally sit folded up in solution, unfold at every new air-water boundary and link to their neighbours, leaving a thin solid film wrapped around each bubble. That film is the foam; everything else is a variable that helps or hinders it.
Fat hinders it more than anything else in the kitchen. Fat molecules crowd onto the same air-water boundary the proteins need but form no film, so bubble walls fail to knit. A drop or two of yolk costs a third of the volume; a teaspoon and the whites will not foam at all. Sugar hinders it differently and more usefully: it thickens the liquid so proteins take longer to arrive, which costs time and some volume, but it also grips water in the bubble walls so the finished foam drains far more slowly.
Keep going past stiff peaks and the same protein links that built the film start over-tightening, squeezing water out and breaking the foam into grainy clumps. Copper bowls are famously forgiving here: traces of copper bind to one of the white's proteins and make that over-tightening much slower, an effect measured and published in Nature in 1984.
How to use this simulator
- Set the number of whites and how much sugar the recipe uses.
- Pick your tool. The gap between a stand mixer and an arm is the biggest single factor in the timings.
- Press play and watch the bubbles subdivide as the foam turns from froth to soft peaks to stiff.
- Now add one drop of yolk and run it again — that one change is worth more volume than any other control here.
- Let it run past stiff peaks to see the foam break, then switch to a copper bowl and see how much longer you get away with it.
Formula
Read these constants as calibration, not chemistry. The directions — sugar trading volume for stability, fat killing foam outright, more whites taking longer — come from the published foam research listed at the bottom of this page. The specific multipliers below are fitted so the output lands where kitchen experience puts it. They are honest about what they are: a curve fit, not a derivation from first principles.
sugar ratio: r = sugar ÷ m
fat fraction: φ = ( drops × 0.17 ) ÷ m
sugar factor: fₛ = 1 ÷ ( 1 + 0.55 · r )
fat factor: fᶠ = max( 0 , 1 − φ ÷ 0.004 )
expansion: E = 8 · fₛ · fᶠ · fₑ
peak volume: V = V₀ · E
stiff peaks at: t = tₜₒₒₗ · √( n ÷ 4 ) · ( 1 + 0.8 · r )
holds for: h = 20 min · ( 1 + 1.6 · r ) · fᶠ · fₕ
- n — number of large whites, 33 g and about 30 ml each
- drops — drops of yolk in the bowl, taken as 0.17 g of fat each
- tₜₒₒₗ — 210 s for a stand mixer, 300 s for a hand mixer, 660 s by arm, for four whites
- fₑ, fₕ — bowl factors for volume and for holding: copper holds 1.35×, plastic 0.9× on volume
- 0.004 — the fat fraction, 0.4%, at which whites stop foaming altogether
Example calculation
4 large whites with 60 g of sugar, no stray yolk, a hand mixer and a glass bowl:
fₛ = 1 ÷ ( 1 + 0.55 × 0.455 ) = 0.80
E = 8 × 0.80 = 6.4 × → V = 120 × 6.4 = 768 ml
t = 300 × √1 × ( 1 + 0.8 × 0.455 ) = 6:49
holds for 20 × ( 1 + 1.6 × 0.455 ) = 35 min
Those are the simulator's starting values and the panel shows the same figures. Add a single drop of yolk and the fat fraction reaches 0.13%, taking a third off the volume — down to 521 ml. Swap the hand mixer for a balloon whisk and the same bowl needs 15:00 of arm work instead. Doubling to eight whites does not double the time: it multiplies it by √2.
What each variable costs you
Expansion for four whites under this model. Weighing whites rather than counting them is worth doing — egg sizes vary by 30% — and the recipe scaler will rebalance the sugar when you do.
Frequently asked questions
Why does a speck of yolk ruin egg whites?
Because fat competes for the same place the proteins need. Foam depends on protein unfolding at the air-water boundary and linking into a film, and fat molecules park on that boundary without forming any film, so the bubble walls never knit together. It takes very little: fat at about 0.1 percent of the whites costs roughly a third of the volume, and around 0.4 percent stops them foaming at all.
When should sugar go in?
After the whites are already frothy, and slowly. Sugar makes the liquid thicker and slows the proteins reaching the bubble surface, so adding it at the start roughly doubles the whipping time and costs volume. Added later it does the useful half of its job: it holds water in the bubble walls, which is why a sugared meringue stays up for hours while plain foam weeps within the half hour.
Does a copper bowl really help?
Yes, and it was measured. Trace copper from the bowl binds to conalbumin in the white and makes the resulting film harder to overbeat, so the foam is more forgiving and drains more slowly. It is a real effect published in Nature in 1984, though a clean bowl and a pinch of cream of tartar get you most of the way there for rather less money.
Related calculators
Assumptions & limitations
- This is a calibrated model, not first-principles physics. The directions and rough magnitudes come from published foam research; the multipliers are fitted so the numbers land where kitchen experience puts them.
- Whites are taken as 33 g and 30 ml each. Real large eggs vary by about 30%, so weigh them if the recipe is tight.
- Sugar is assumed added once the whites are frothy. Tipping it in at the start costs more time and more volume than modelled.
- No cream of tartar, salt or lemon juice. A little acid speeds foaming and improves stability; salt does the opposite.
- Temperature is not modelled. Room-temperature whites whip faster than fridge-cold ones, and warm sugar syrup — the Italian meringue route — changes the picture completely.
- Baking is out of scope. This stops at the bowl: what the oven does to the foam afterwards is another matter.
Further reading
Our guide to kitchen chemistry covers protein denaturation as one idea running through foam, curdling and cooked egg alike. The rest of The Kitchen & Gut Lab covers the other places protein structure decides whether a dish works.
Sources & references
The composition figures and the behaviour this model is calibrated against come from the following, all specific to egg white foams.
- USDA FoodData Central — raw egg white composition, the protein and mass figures used per white
- Foegeding, Luck & Davis (2006), Food Hydrocolloids — what determines the physical properties of protein foams, including lipid inhibition
- Yang & Foegeding (2010), Food Hydrocolloids — effects of sucrose on egg white foams, the basis of the sugar trade-off between volume and stability
- McGee, Long & Briggs (1984), Nature — why egg whites are whipped in copper bowls