Scaling a Recipe Up or Down Without Ruining the Result
Most main ingredients (the primary protein, vegetables, flour in a straightforward recipe) scale reliably in direct proportion to the serving size change, but leavening agents, spices, salt, and cooking liquids often don't scale perfectly linearly and benefit from adjustment to taste after scaling, rather than a strict proportional multiplication.
Knowing which categories of ingredients scale reliably and which need a closer eye is the key difference between a scaled recipe that works and one that comes out noticeably off.
What scales reliably
Primary ingredients that make up the bulk of a dish — the main protein, vegetables, grains, and flour in most straightforward recipes — generally scale in direct proportion to the serving size change without issue, since their role in the dish is largely additive rather than requiring a specific balance against other ingredients.
What needs adjustment to taste
Leavening agents (baking powder, baking soda, yeast) often don't need to scale perfectly linearly, since their effect isn't strictly additive — doubling a recipe doesn't always mean exactly doubling the leavening. Salt, strong spices, and other potent flavorings are also commonly better adjusted to taste after scaling rather than multiplied strictly, since perceived intensity doesn't always scale linearly with quantity.
A practical scaling approach
Scaling the main bulk ingredients directly by the multiplication factor, then adding leavening, salt, and strong spices at a slightly more conservative amount than a strict proportional scale-up (tasting and adjusting as needed), tends to produce a more reliable result than a uniform multiplication applied to every single ingredient without exception.