Excerpt of Search API index is cached
Thanks to berramou!

I ended up using this in my theme:

/**
 * Implements hook_preprocess_HOOK().
 */
function MYTHEME_preprocess_node(array &amp;$variables) {
  if ($variables['view_mode'] == 'search_result') {
    $variables['#cache']['max-age'] = 0;
  }
}