A slice of kiwi is among the most eye-catching fruits on a cake. Its green colour and symmetrical pattern of seeds appear in no other fruit.
What are the two problems with fresh kiwi?
The first problem is water.
Kiwi is 83 percent water by weight.
That water seeps from the cut surface.
A pool of liquid forms on the cream.
The colours run.
The cake loses its appearance within two hours.
The second problem is an enzyme.
Kiwi contains a protease called actinidin, and that enzyme breaks down gelatine and milk proteins; the result is a layer of dissolved cream on top of the cake.
| Method | Life of appearance | Water seepage | Enzyme effect |
|---|---|---|---|
| Fresh slices, directly | 1-2 hours | High | Present |
| Fresh slices, glazed | 6-8 hours | Moderate | Partly prevented |
| Freeze-dried | 4-6 hours | None | None |
| Freeze-dried, glazed | 24 hours | None | None |
| Candied kiwi | 24 hours | Low | None |
| Kiwi powder | Indefinite | None | None |
What does actinidin do?
That enzyme is a natural component of kiwi.
A protease that breaks down proteins.
Its effect shows in two places in a kitchen.
The first is gelatine; jelly with kiwi in it will not set.
The second is dairy; leave kiwi on cream or a custard and the surface turns liquid.
Heat deactivates the enzyme.
Boiled kiwi purée can go into a jelly.
Freeze-drying has a similar effect; because water activity falls so far the enzyme cannot work, and the slice sits on cream for a long time without trouble.
What advantage does a freeze-dried slice provide?
Three advantages stand out.
There is no water; no liquid seeps once it sits on the cream.
The enzyme is inactive; gelatine and milk proteins survive.
And the pattern shows; the seed pattern and green colour survive the drying.
The slices are also uniform and flat; thickness varies in fresh kiwi because it gets cut by hand.
The disadvantage is a fragile texture; being thin and hard the slice can break while handled, so it gets placed carefully.
When does it go on?
Timing decides half the result.
A freeze-dried slice draws moisture.
It begins softening on cream within two or three hours.
That softening does not spoil the appearance immediately; the colour and pattern hold a while longer.
But the crispness goes.
The decoration therefore happens two or three hours before service.
Where it has to be made earlier, a thin layer of glaze goes under the slices.
The glaze acts as a barrier and delays the transfer of moisture; that method extends the period to twenty-four hours.
Which pattern layouts get used?
A kiwi slice is round and symmetrical, which suits regular patterns.
The first layout: a border ring.
The slices go around the rim of the cake in a circle.
The centre stays empty or carries writing.
The second layout: full coverage.
The slices overlap across the whole surface.
The third layout: a central rosette.
The slices spiral outward from the centre like a rose.
The fourth layout: scattered; the slices go on in different sizes at random positions, which gives a more modern look.
How is the colour balanced?
The green of kiwi is a strong colour.
Colours placed beside it get chosen carefully.
Red is the strongest contrast; it gets used with strawberry and sour cherry.
Yellow and orange give a softer transition; mango and apricot suit.
White is a neutral ground; white cream brings the green forward.
Kiwi stands out clearly on chocolate-covered cakes, though the match in flavour is weak.
Blue and purple tones clash with kiwi; placed beside blackberry and blueberry both colours look muddy and the pattern does not read.
How do the slices get fixed?
A dried slice is light and does not settle into cream.
Three methods get used.
The first presses lightly; the slice sinks half a millimetre into the surface of the cream.
The second uses a drop of glaze; a small point goes under each slice.
The third uses syrup; a thin sugar syrup goes onto the underside.
Pressing is the simplest and the least durable.
Glaze is the most durable but takes time to apply; where a cake has to travel the glaze method gets chosen and the slices do not slide on the way.
Does it get used as a powder?
It does, and that gives a different effect from slices.
The slices get ground.
A pale green powder results.
That powder gets stirred into cream, giving colour and a slight acidity.
Or it gets dusted over the cake through a stencil.
A pattern forms.
Because the powder draws moisture it goes on close to service.
Powder left standing darkens at the surface and leaves a blotchy look; the stencilling therefore happens as the final step.
How is a decorated cake stored?
A cake decorated with kiwi goes into a fridge.
But it needs a closed box.
The slices draw the humidity of the fridge on a cake left uncovered.
The box slows that transfer.
It comes out twenty minutes before service.
That time lets the cream soften.
Leftover cake gets eaten the same day; on a cake left to the next day the slices have softened completely and their colour faded, so the decoration gets redone.
How does it work with other fruits?
Kiwi works alone but proves more effective in a mixed decoration.
It forms a classic pair with slices of strawberry; red and green make a strong contrast.
Slices of orange add a third colour.
Slices of banana provide a neutral transition.
Every fruit should share the same thickness in such a decoration.
Different thicknesses make the surface look irregular.
That problem disappears with freeze-dried products; all of them get cut to one size at the factory and the surface stays even.
