Are berries acidic enough they must be on top, not within, panna cotta?

Item 1 Panna cotta (cream, gelatin, perhaps sugar)

Item 2 berries (blueberries, blackberries, raspberries, strawberries)

Stores usually sell panna cotta with the berries on top. Is this just because it is more presentable, or is there a technical reason?

In particular, would the cream go sour if the panna cotta is poured over the berries so that the berries are fully buried inside? Are berries acidic enough for this to happen?

Reasons for putting the berries inside? There are at least two:

Nudge kids to eat the fruits. "You want the nice cream; you've got to have the berries along with it."
The two flavors mix better, and (imagining) the berries will last a day or two in the fridge without the skin "wilting".

Best Answer

Reporting experimental results.

I hypothesized that frozen berries will fare better than fresh. The reasoning? It will take them a while to thaw if the cream is poured at room temperature and put in the fridge right after. By the time they thaw, the cream would have set.

In practice, it's more complicated. Alchimista's hunch is accurate. The skin of the berries is not as impermeable as one would think (I skipped strawberries, since they're inherently porous).

Perhaps the berries will keep just as well inside as outside; that is not entirely clear. But the cream will not set as well near the surface of the berries as it sets farther away, and soggy panna cotta seems like a candidate for going bad sooner.

All in all, I'd say keeping the berries on top is a better option. Besides, an enhanced presentation is a good attribute for homemade desserts as well.