Scaling recipes: why simply doubling does not always work

It looks like basic arithmetic: recipe for four, eight guests, so everything times two. For a large share of the ingredients that is exactly right. Yet anyone who regularly cooks for groups knows the failures: the soup that came out too salty, the stew that refused to thicken, the cake that went into the oven doubled and came out like a wet sponge. Scaling is basic arithmetic plus a handful of exceptions, and the exceptions decide whether it works.

What can simply scale linearly

The main ingredients (vegetables, meat, fish, pasta, rice, pulses) scale without trouble. Twice the guests, twice the potatoes: nothing ever goes wrong here. Liquid in soups and stews may also scale linearly at first, with one caveat below.

What to hold back

• Salt and stock cubes. Evaporation concentrates salt, and at larger volumes the evaporation ratio changes. Scale salt to three-quarters of the factor and adjust at the end by tasting. You can always add salt; you cannot take it out.
• Heat and strong spices. Chilli and assertive spices (clove, cinnamon, bay) seem to land harder at volume. Same rule: three-quarters, then taste. Three bay leaves in a double stew is plenty; six is a medicine cabinet.
• Garlic and onion in raw applications. In a dressing or tzatziki, raw garlic counts double; one and a half times is usually the maximum when doubling.
• Acid and alcohol. Scale wine, vinegar and lemon conservatively at first; restore the balance at the end, while seasoning to finish.

The common thread: anything that concentrates or dominates flavour is scaled cautiously and corrected by tasting. Anything that is volume and filling scales straight along.

The pan is half the story

Many "scaling failures" are really pan failures. Twice the mince in the same frying pan does not brown but boils in its own juices, because per centimetre of pan floor there is suddenly twice as much cold material. Rules that help:

• Brown in batches when the pan does not grow with the recipe. Better to sear perfectly twice than to stew grey once.
• Soup and stew mostly need capacity; a bigger pot solves it. But allow longer times: a double pot of soup comes to the boil more slowly, and a double stew needs longer to go tender. The meat's doneness is the clock, not the recipe.
• Bakes and gratins: better two dishes than one deep one. Surface area drives crust and cooking; a layer twice as thick cooks fundamentally differently.
• Evaporation scales with the pan's surface, not its volume. A sauce that should "reduce by half" takes far longer in a big pot of the same diameter. Judge by thickness, not by the clock.

Baking is the exception that truly counts

For bread, cake and pastry, scaling is chemistry. The ratios of flour, moisture, fat and raising agent are tight, and baking time depends on shape. A double quantity of cake batter in a double-size tin does not bake twice as long, but differently: the outside is done while the middle is still liquid.

The safe route with baking: double the recipe, but bake in two of the original tin. If you insist on one large tin, lower the temperature slightly, extend the time, and test with a skewer instead of trusting the clock.

Scaling down has rules of its own

Halving looks easier, but small quantities are more sensitive: half an egg is impractical (beat the egg and weigh half), a quarter teaspoon of yeast demands precision, and in an oversized pan a small amount of fond burns fast. Here too: shrink the pan along with the recipe, re-judge timings, and season slightly more generously than half, because short cookings of small volumes lose relatively more aroma.

Do not let the arithmetic be the failure

The silliest scaling errors are not cooking errors but maths errors: working out 1.5 times two-thirds of a cup in your head mid-chopping goes wrong eventually. Convert everything before you start and write the new quantities down, on paper or in your app; in a digital cookbook like Recettino the ingredient list rescales automatically to the number of guests, which keeps your head free for the part that genuinely needs it: tasting, watching and adjusting in time.