Code:
//opengraph
$descog = JHtml::_('string.truncate', strip_tags($this->product->product_desc), 300);
$descog = trim(str_replace('Description','',$descog));
$descog = trim(str_replace(' ','',$descog));
$descog = trim(preg_replace('/[\t\n\r\s]+/', ' ', $descog));
$document = JFactory::getDocument();
$document->addCustomTag('<meta property="og:type" content="product" />');
$document->addCustomTag('<meta property="og:title" content="'. $product->product_name .'" />');
$document->addCustomTag('<meta property="og:description" content="'.htmlspecialchars($descog).'" />');
$document->addCustomTag('<meta property="og:url" content="'.JURI::current().'" />');
$document->addCustomTag('<meta property="og:image" content="'.JURI::root() . $product->images[0]->file_url .'" />');
$document->addCustomTag('<meta property="product:availability" content="instock" />');
$document->addCustomTag('<meta property="product:condition" content="new" />');
$document->addCustomTag('<meta property="product:retailer_item_id" content="'. $product->virtuemart_product_id .'" />');
Je ne suis pas du tout programmer donc on m'a aidé pour ce code dans le forum de Virtuemart