How to convert PHP object array to JSON

Question

I am trying to learn Angularjs and today I have a PHP5 application, but I am not using Restful. For testing purposes I want to run my query and fill a table with the result using Angularjs. My problem is that I run the search inside the class through the method I created, and it obviously returns an array with each object and its properties according to the query. I searched and tried using the following line to convert my array to JSON and use Angularjs, but my return is being empty.

$cervejas = new Cerveja();
$lista = $tt->listar();
echo json_encode($lista);

But then I couldn’t print my object array. PS: if I give one

print_r ($lista);

The array has the contents.

Array ( 
[0] => Cerveja Object ( [id:Cerveja:private] => 2 [nomeCerveja:Cerveja:private] => Cerveja 1 ) 
[1] => Cerveja Object ( [id:Cerveja:private] => 3 [nomeCerveja:Cerveja:private] => Cerveja 2 ) 
[2] => Cerveja Object ( [id:Cerveja:private] => 6 [nomeCerveja:Cerveja:private] => Cerveja 3 ) 
)