We have a new home and a new refrigerator. The refrigerator is plugged into a standard outlet and on the same circuit is one GFCI. While using a hand mixer on the GFCI outlet the circuit breaker - not the GFCI - tripped twice and that, of course left us with no power to the refrigerator - until we reset the breaker. We figured the mixer was the problem although we didn't understand why the circuit breaker tripped and not the GFCI. We just aren't comfortable with a situation where we could leave for a few days and come back to a dead refrigerator. Question one is, in new construction these days is the general practice of providing a refrigerator its own circuit no longer an issue? Question two is if the mixer was the problem why wouldn't it trip the GFCI before tripping the circuit breaker?
Refrigeration equipment may be served from another circuit aside from the kitchen circuits but it is not required.
210.52(B) Small Appliances.
(1) Receptacle Outlets Served. In the kitchen, pantry, breakfast room, dining room, or similar area of a dwelling unit, the two or more 20-ampere small-appliance branch circuits required by 210.11(C)(1) shall serve all wall and floor receptacle outlets covered by 210.52(A), all counter-top outlets covered by 210.52(C), and receptacle outlets for refrigeration equipment.
Exception No. 1: In addition to the required receptacles specified by 210.52, switched receptacles supplied from a general-purpose branch circuit as defined in 210.70(A)(1), Exception No. 1, shall be permitted.
Exception No. 2: The receptacle outlet for refrigeration equipment shall be permitted to be supplied from an individual branch circuit rated 15 amperes or greater.
As to why it is tripping the breaker, I think you apparently have too much on one circuit and the addition of the mixer put it over the top. A GFCI trips if current is diverted outside the normal circuit path and the breaker trips if the normal circuit is overloaded. You may have had the microwave or another appliance running with the fridge and mixer.
Moving the fridge to its own circuit would make good sense in this case.
A refrigerator does not have to be on a dedicated circuit, it's simply a convention some builders/Electricians follow.
A ground-fault circuit interrupter (GFCI) trips in response to a ground-fault. While a standard circuit breaker trips in response to overloads, and overcurrents.
If the combined current drawn of the refrigerator, mixer, and whatever else was connected, is greater than the breaker rating (for long enough). Then the breaker would trip, but the GFCI would not.
If there was a ground-fault. The GFCI would trip, but not the breaker.
They are two different types of devices, designed to provide different types of protection.
Your refrigerator should be on its own circuit. A refrigerator and hand mixer could easily draw 15 amps that would trip a 15 amp bkr, the GFCI is only looking for ground faults. The model of both appliances would allow us to look up the power they draw. Kitchen circuits in newer houses are supposed to have a minimum of 2 circuits to service the countertop area.
I'll add one last thing.. as it seems to be your worry. Your breaker will not trip while you're gone from the house as long as those other loads are not turned on. If you're not home, then I'm guessing that the hand mixer won't be on and so the breaker won't trip. Figured it was at least worth mentioning.
It's typical to give a refrigerator it's own dedicated circuit nowadays and I'd still recommend you doing it as well to end your problems.