$.fn.beer = function(settings) {
  settings = $.extend({ url: "/", container: "#id-of-container" });
  return this.change(function() {
    var val = $(this).val();
    $.post(settings.url, val, function(response) {
      $(settings.container).html(response);
    });
  });
}

$(document).ready(function() {
  $('#id-of-input').beer({ url: '/url/to/post/to' });
})