Magic Freezer/Fridge

A gifted mercere in my campaign wants to give an NPC Redcap (Aristides of the Theban Tribunal) a gift, namely that of a magic container that can freeze his food while he is out sailing.
The parameters she wants to have on this item are:

[list=]1. Container shall freeze food that is put in and be able to be removed when "door" is open.
2. Container should be able to be used 3 times per day.
3. Aristides must not get his hands frozen while putting in & removing frozen food.
4. Preferably Perdo Ignem.
5. She is newly Gauntleted and is a generalist so she wants it as simple as possible. [/list]

Form bonus: Container (+5 affect items within)

From what I see the Base is 5 (Strongly freeze an object, for example freeze water).

How should she do it?

In this case:

PeIg Base 5
Range: Touch (+1)
Duration: Ring (+2)
Target: Circle (+0)
Frequency 3 uses/day (+2 levels)

Total: PeIg Effect Level 22

A wooden empty sphere arranged to open in a way that breaks a ring drawn about it. The food is put within, and then the device is activated, up to three times per day, by tracing over the ring. It instantly freezes the contents. Opening the sphere breaks the ring, and hence the spell, instantly returning them to their usual temperature.

Unfortunately, that's only true if the creator of the item has the flaw Harmless Magic. Otherwise a perdo spell is naturally permanent once its duration ends (unlike creo spells). Destroyed things don't return at the end of the duration.

Is instantly freezing food really very useful? You presumably want to stock it in port, and then remove things as you need them.

Personally I'd probably recommend targeting a reasonable chunk of water, and turn it into ice, then you have an icebox. You can put items in the icebox to keep them chilled, or if placed within the ice (which can be hollowed out, as it will never melt) even keep them frozen.

A magical fridge, however, is easy. It can be achieved with either perdo ignem (R: Touch, D: sun, T:Ind= level 23 item for continuous effect) to remove heat or rego aquam (Base 3, Touch+1, sun+2, +3 environment trigger= level 13 item) to turn water into ice.

The rego aquam enchantment is particularly easy, and therefore probably worth considering.

Why is REgo AQuam turning water to ice, I thought that should be muto.

Ice is a natural form/condition for water, so changing to it is Rego. Being sparkling orange, for example, is not a state water may change into naturally, so changing water to be sparkling-orange is Muto.