MiddleWare for Roles?

Hi, Why isn't this working:

<?php namespace App\Http\Middleware;

use Closure;
use Illuminate\Contracts\Auth\Guard;

class AdminAuthenticate {

    protected $auth;
    
    public function __construct(Guard $auth)
    {
        $this->auth = $auth;
    }

    public function handle($request, Closure $next)
    {
        if ($this->auth->guest() || $this->auth->role != 'admin')
        {
            if ($request->ajax())
            {
                return response('Unauthorized.', 401);
            }
            else
            {
                return redirect()->guest('auth/login');
            }
        }

        return $next($request);
    }

}

And for the controllers:

public function __construct()
    {
        $this->middleware('authAdmin');
    }

Kernel

protected $routeMiddleware = [
        'auth' => 'App\Http\Middleware\Authenticate',
                'authAdmin' => 'App\Http\Middleware\AdminAuthenticate',
        'auth.basic' => 'Illuminate\Auth\Middleware\AuthenticateWithBasicAuth',
        'guest' => 'App\Http\Middleware\RedirectIfAuthenticated',
    ];

I want a Middleware, so only Users that are logged in and have as role in the Usertable "admin".