Well, there is one but ugly way - via iterating over its nodes:
$html = '';
foreach ($crawler as $domElement) {
$html.= $domElement->ownerDocument->saveHTML();
}
Or, in your case, you should iterate over filtered element:
$html = '';
$product = $crawler->filter('#produkt');
foreach ($product as $domElement) {
foreach($domElement->childNodes as $node) {
$html .= $domElement->ownerDocument->saveHTML($node);
}
}
From documentation