Set model not consoled by JSON stringify - what is wrong?

I am setting some value to model like :

afterModel:function(model,transation){
        Ember.set(model, 'processedTrans', 'TechMahindra');
    },

when i require the value I used to get : model.get('processedTrans') - works fine. But in case if I do:

JSON.stringify(model) - I am not finding the value what i set in the afterModel method. what is the issue here? or do i require to add any additional stuff to get in json string? Really what i set is my models property?

any one help me to understand this?