You double a recipe that has worked for years. Every quantity times two, cleanly calculated, nothing forgotten. And then the sauce is too thin, the meat raw in the middle and the whole thing too salty.
What happens if you simply double a recipe?
The ingredient list is right, and the dish is not.
It is not the arithmetic. The multiplication is trivial and it was correct: for simply converting portion quantities our free recipe scaler is enough. When a doubled recipe turns out badly, it is almost never a miscalculation.
The reason lies elsewhere, and it fits into one sentence. Mass scales; time, surface area and perception do not.
A recipe is a list of masses, and masses can be multiplied. What else determines the result is not on that list: how long something takes, how much water evaporates, how strong it tastes and what fits in the pan in the first place. None of these four behaves in proportion to the amount.
What scales linearly and what does not?
Almost all ingredient quantities do. Four things do not, and a fifth is a limit.
| Scales linearly? | Why | |
|---|---|---|
| Ingredient quantities by weight | Yes | Pure multiplication, nothing more happens |
| Cooking time | No | Depends on the thickness of the piece, not on the total mass |
| Reduction and evaporation | No | Happen at the surface, and the surface does not grow with the volume |
| Salt and strong spices | No | Were adjusted to taste, not calculated |
| Leavening and fermentation | No | Time and temperature act on the whole mass, not per portion |
| Equipment capacity | No | Not an ingredient but a limit |
| Allergens | Unchanged | More quantity, not different ingredients |
Once you know the reasons, you no longer need the table: you see for yourself where the next recipe will run into trouble.
Why is the cooking time no longer right?
Because cooking time depends on thickness, not on weight.
Heat travels from the outside in. How long a piece takes is decided by the distance the heat has to cover to reach the centre. That distance does not get longer when a second piece sits next to the first.
Something follows from this that contradicts intuition: two roasting joints of the same size take roughly the same time as one. Not twice as long. This assumes the oven holds its temperature and the air can circulate between the pieces; otherwise the oven cools as you load it and the result shifts after all.
The reverse is just as true, and this is where it gets expensive: a piece twice as thick takes considerably longer than two separate ones. If you take one large joint instead of two, you do not have a doubled recipe; you have a different dish with a different cooking time.
In the pot it is the same idea. Twice the stew in the same pot sits higher, and the heat from the base has further to travel before it reaches the top. Two shallower pots come closer to the original recipe than one filled to the brim.
In practice this means: do not scale the time up, look at the geometry. If the piece size stays the same and only the number of pieces grows, the time stays roughly the same too. If the thickness of the piece or the fill level in the vessel changes, the time changes, and not in the same ratio as the quantity.
A note on scope: this is about the result on the plate, not about food safety. Core temperatures, chilling and hot-holding times are a separate topic and are not covered in this article.
Why does the sauce not thicken, and why does it taste different?
Two different reasons.
The sauce first, because it can be worked out in advance. A pot has a fixed diameter. The liquid evaporates at its surface, and that is the circle at the top of the pot. Double the quantity in the same pot and the height of the liquid doubles. The surface area stays exactly the same.
So the same amount evaporates per minute as before, but there is twice as much of it. Reaching the same consistency takes roughly twice as long. What helps is a different vessel: wider rather than taller, or two pots side by side instead of one filled to the brim.
And then the seasoning. Salt and strong spices were adjusted to taste in the original recipe, at one particular quantity. That was a decision made at the stove, not a calculation step, and so it does not transfer cleanly to a different quantity.
At this point almost every guide prints a number: scale salt only to such-and-such a percentage, spices by this or that factor. There is no number here, and that is deliberate. There is no reliable source for those numbers; they depend on the dish, the spice and the cooking time, and an invented rule is worse than none. The approach that holds: scale up linearly, like everything else, and then season to taste before it goes on the plate. Anyone who knows their own figure, because they often cook the same dish at both sizes, writes it down and has more to go on than any rule of thumb from the internet.
What else changes that is not in the recipe?
Three things, and none of them appears on an ingredient list.
Equipment capacity, and this is the hardest limit. Past a certain point the problem is no longer the recipe; it is that the pan is full. Whatever is packed in too tightly no longer fries, it steams, because the moisture cannot escape. The same goes for the blender, the oven and the tilting pan. This limit does not announce itself, it is simply there, and beyond it every extra kilo comes out worse rather than just as good.
The divisibility of the batch. Some recipes cannot be halved, because half an egg is not a usable quantity. That is not an arithmetic problem but a property of the recipe, and it belongs on the recipe card.
The yield. It can shift with batch size, because larger quantities get trimmed and cooked differently. If you cost with yield-adjusted prices, check it on the first large batch (how to measure the value).
And one thing does not change at all: the allergens. More portions mean more quantity, not different ingredients (more on this).
How do you scale a recipe properly?
Scale up linearly, check four things, season to taste and write the result down.
- Scale the quantities up linearly. All of them, without exception, including salt and leavening. That is the starting point, not the end result.
- Check four points the arithmetic does not cover: do the cooking and proving times still hold, or does the thickness of the piece or the fill level change? Is there enough surface area for reducing? Does the equipment hold the quantity? And can the batch even be divided this way?
- Season to taste before it goes on the plate. Not right before plating, but early enough that a correction is still possible. If a sauce keeps reducing after that, check the seasoning again once it has reached its final consistency: water evaporates, the salt stays.
- Write down the adjusted version. What you changed, at which batch size and in which vessel.
The fourth step is the one almost everyone skips, and it decides whether the work is done once or has to be done again on the next occasion. Without a note, the same person faces the same problem next time and guesses again. The place for it is the recipe card, which carries the batch size anyway: a second line for the large version, and the question is answered once and for all.
How far can software help you scale a recipe?
For the conversion itself there is our free recipe scaler. Quantities to any portion count, instantly and without a login.
When one recipe turns into a range, that is what we are building Trolevo for: recipes with nested sub-recipes, plus the costing and the allergen label on the same basis. A base recipe that sits in several dishes is maintained once rather than redone in every dish.
What neither of them does, plainly, is exactly the limit this article describes: neither adjusts cooking times, salt or leavening. Neither factors in your pots, your oven or how high your sauce sits in the pot. That helps with the arithmetic; seasoning to taste stays with you.
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