How to print meta property using custom meta tag module
Telling your custom meta tag to use the property theme formatter should do the trick.

$info['tags']['my_custom_metatag'] = array(
  'label' =&gt; t('My Custom Meta Tag'),
  'description' =&gt; t('This is a custom meta tag'),
  'class' =&gt; 'DrupalTextMetaTag',
  'group' =&gt; 'my_metatags',
  'element' =&gt; array(
    '#theme' =&gt; 'metatag_property',
  ),
);