A simple way to render Twig template from a string... ? Seems to work for me.

gistfile1.php

# This is pretty much pilfered from: http://twig.sensiolabs.org/doc/recipes.html#using-a-database-to-store-templates
# and then modified to use a given strings for templates instead of fetching from the database... even simpler!

# The loader as a component:

class TwigString implements \Twig_LoaderInterface {

    public function getSource($name)
    {
        // get from database
        return $name;
    }

    public function isFresh($name, $time)
    {
        // determine from database
        return true;
    }

    public function getCacheKey($name)
    {
        // check if exists
        return 'twigStringService:' . $name;
    }

    public function render($string, $variables) {
        $twig = new \Twig_Environment($this);
        return $twig->render($string, $variables);
    }

}

        
# And, using it in a controller:

    public function indexAction(Request $request) {
        ...
        // Spelled out...
        $twigString = new TwigString();
        $template = 'Hello {{ name }}';
        $variables = array('name' => 'Jason');
        $rendered = $twigString->render($template, $variables);
        // Or in one line...
        $rendered = (new TwigString())->render('Hello {{ name }}', array('name' => 'Jason'));
        ...
    }