Fruit sinks in a cake, and tossing it in flour is not the fix

There is a short answer about fruit in cakes and a useful one, and they are not the same. What follows is the useful one.

What is actually happening

A cake batter is a liquid until the heat sets the proteins and gelatinises the starch, which takes some minutes in the oven. During that window anything denser than the batter will move downwards, and fruit is usually denser than batter. The question is therefore whether the batter is thick enough to resist that movement for long enough.

A thin batter offers almost no resistance, and no treatment of the fruit will change that fundamental fact. A thick batter can suspend quite heavy pieces without any special measures at all.

Why the flour trick underperforms

The theory is that a flour coating grips the batter and holds the fruit in place, which sounds plausible. In practice the coating is thin, it hydrates almost immediately in a wet batter, and the density difference remains. It does have one real benefit, which is absorbing surface moisture on wet fruit so the batter is not thinned locally.

On a weeknight, that is a genuine but modest effect, and it is not what most people believe they are achieving. It is a useful step rather than a solution, and relying on it alone usually leads to disappointment.

Thicken the batter instead

A stiffer batter is the single most effective change, and it comes from the ratio of liquid to flour rather than from any additive. Recipes designed for a heavy load of fruit are noticeably thicker than plain cake recipes for exactly this reason. Reducing the liquid slightly in an existing recipe is a reasonable adjustment when adding a large quantity of fruit.

At the stove, creamed batters tend to be thicker than melted or all-in-one ones, which is why they hold fruit better. Adding a small amount of extra flour changes the crumb too, so the adjustment should be modest and tested.

Size, weight and moisture of the fruit

Small pieces distribute more evenly and sink more slowly than large ones, simply because there is less mass in each. Very wet fruit both weighs more and thins the batter around it, which compounds the problem in two directions. Draining tinned or macerated fruit thoroughly, and patting fresh fruit dry, addresses the second of those.

Dried fruit is lighter than fresh and stays suspended far more readily, which is why heavy fruit cakes work at all.

Cutting large fruit into smaller pieces is often more effective than any of the standard tricks.

Layering and placement

Spooning half the batter in, adding the fruit and covering it with the rest physically holds the fruit above the base. This works, though it produces a visible layer rather than an even distribution. Scattering some fruit on top before baking gives an attractive surface and sinks less than fruit stirred through.

A hotter start sets the outer structure sooner, which reduces the window during which sinking can happen. Combining a thicker batter with smaller drier fruit and a decent oven temperature solves the problem more reliably than any single measure.

When sinking does not matter

A layer of fruit at the base is only a problem if you consider it one, and some cakes are built around exactly that. Upside-down cakes formalise the effect rather than fighting it, and they are easier for exactly that reason. A dense fruit-heavy cake with everything at the bottom can be turned out and served as though it were intentional.

At the stove, the genuine problems are a soggy base and an unbalanced crumb rather than the distribution itself. Deciding whether you actually mind is worth doing before adjusting a recipe that otherwise works well.

The takeaway

Thicken the batter, dry and shrink the fruit, and stop relying on a spoonful of flour to do the work.

Taste it before it leaves the pan. That is most of cooking.