function custom_single_product_summary(){
  $maxWords = 50; // Change this to your preferences
  $description = strip_tags(get_the_content()); // Remove HTML to get the plain text
  $words = explode(' ', $description);
  $trimmedWords = array_slice($words, 0, $maxWords);
  $trimmedText = join(' ', $trimmedWords);

  if(strlen($trimmedText) < strlen($description)){
    $trimmedText .= ' &mdash; <a href="' . get_permalink() . '">Read More</a>';
  }

  echo $trimmedText;
}