Debug not creating debug.log

WP3.9.2 is not creating or updating the log file in wp-content.
I have created a small error in a plugin, which is being reported to the display, so I know debug is working and there is an error to report.
I believe config.php is correct, as follows:

* For developers: WordPress debugging mode.
 */

//INSERTED TO ADD DEBUG TO A FILE
// Enable WP_DEBUG mode
define('WP_DEBUG', true);
//define('WP_DEBUG', false);

// Enable Debug logging to the /wp-content/debug.log file
define('WP_DEBUG_LOG', true);
//define('WP_DEBUG_LOG', false);

// Disable display of errors and warnings
define('WP_DEBUG_DISPLAY', true);
//define('WP_DEBUG_DISPLAY', false);
@ini_set('display_errors',0);

// Use dev versions of core JS and CSS files (only needed if you are modifying these core files)
//define('SCRIPT_DEBUG', true);
define('SCRIPT_DEBUG', false);

Can anyone point me in the right direction?
Thanks