Here is an explaination of what gruit is from www.gruitday.com
What is Gruit Ale?
Centuries ago it would have seemed odd to consider using only one herb to spice beer. Dozens of plants, such as bog myrtle, yarrow, mugwort, heather, and juniper were commonly used in ancient brewing, providing beer makers with a wide array of aromatic and flavourful options. These beers were known as Gruit or Grut (German for herb), and a brewers’ spice blend was a proprietary and carefully guarded secret. However, after the Reinheitsgebot (Bavarian Purity Act of 1516) ordered that only hops were to be used to spice beer, and the Bavarian style of brewing took hold in most of Europe, the Gruit Ale gradually faded into obscurity.
Luckily, several craft breweries have rediscovered this ancient form of brewing. Craft brewing is based on the notion that beer should not be limited by the conventional norm – that beer should be about discovery and experimentation, and Gruit Ales are one of the best examples of this pioneering spirit.
The craft brewers who produce Gruit Ales have banded together to mark February 1st as International Gruit Day. On this day, brewers and beer enthusiasts around the world pay homage to our brewing past and our exciting future as we rediscover the taste and excitement of this ancient libation.