Issue to change text_format

Hi, i'm italian so excuse me for my english, anyway i'm trying to change $form['recipe_description'] #type. I've changed some line of code to make some personalizations. Now i'm using this code

$form['recipe_description'] = array(
[...]
    '#type' => 'text_format',
    '#wysiwyg' => false,
    '#format' => isset($node->format) ? $node->format : 'plain_text',
    '#default_value' => !empty($node->recipe_description) ? $node->recipe_description : '',
[...]
  );

but i want change it into this:

$form['recipe_description'] = array(
[...]
    '#type' => 'textarea',
    '#default_value' => !empty($node->recipe_description) ? $node->recipe_description : '',
[...]
  );

When i submit my recipe, it saves only the first letter in the textarea. Why? Can i do something to fix it?