Gluten-free beer is beer made from ingredients that do not contain gluten. People who have gluten intolerance (including celiac disease and dermatitis herpetiformis sufferers) have a reaction to certain proteins in the grains commonly used to make beer, barley and wheat. The hordein found in barley and the gliadin found in wheat are types of gluten that can trigger symptoms in sufferers of these diseases. Gluten-free beer is part of a gluten-free diet.
Gluten and gluten intolerance
Gluten can be found in many common cereal grains including barley and wheat. Even in small quantities, the glutens specifically from barley and wheat (hordein and gliadin respectively) can trigger serious symptoms in those who suffer from Celiac disease. Almost all beer contains levels of gluten that cannot be tolerated by the celiac, but a growing number of breweries now cater to celiacs or those who otherwise cannot tolerate the consumption of one or other of the relevant glycoproteins.
Around the world standards of "gluten free" vary. For example, in the European Union a beer with less than 20 parts per million gluten (20ppm) is "gluten free", while in Australia only beers with no detectable gluten can be described as gluten free. Similarly, some "gluten-free" breads can contain low levels of gluten in one country, in another they would contravene labelling or food standards legislation.
While the definitions of world standards for the term "gluten free" vary, the safest course of action for people with celiac disease would be to adhere to strictest possible definition (no detectable gluten).
No published long term studies exist that track the effects of the consistent use of low levels of celiac-triggering glutens on patients with celiac disease, while many published papers exist that document the damage these glutens cause.
Gluten-free beer, low-gluten beer, and standard beer
Beers brewed mainly from cereals such as millet, rice, sorghum, buckwheat and corn (maize), which do not contain gluten, do not trigger an autoimmune response in celiacs. Some brewers brew with barley or rye, and reduce the level of gluten to below 20 ppm. In most countries this technically classifies them as gluten-free beers. These brewers believe they are safe to drink. The brewers argue that the proteins from barley are converted into non-harmful amino acids. Statements from brewers show that their scientists feel confident that their product is non-harmful to those who are gluten intolerant. Some celiacs report problems drinking these beers. However, there is some concern and evidence that the claim is not true.(for example: Sheehan, Evans & Skerritt, 2001).
Brewers who produce low gluten beers are required to test every batch for gluten, and record gluten levels in "parts per million" ('ppm'). Although the barley hordeins in such tests may not be detected, smaller pieces of these proteins, known as peptides, may remain and be toxic for celiacs. Those involved in gluten-free brewing, and others representing celiacs or those with other conditions that require a gluten-free diet, tend to be concerned that beer brewed using wheat or barley are not appropriate for those with celiacs or dermatitis herpetiformis, although the carefully controlled gluten levels of particular malt brews of England and Finland may be low enough to be consumed in relative safety (Against the Grain, 5 ppm; Sinebrychoff Koff III, 20 ppm; Laitilan Kukko Pils, 4 ppm).
In August 2013 the FDA approved labeling standards for what constitutes gluten free for food sold within the United States, and the standards require that the food or beverage test below 20 PPM of gluten to be labeled as gluten free. Some beers that are not traditionally sold as gluten free have been shown to meet this criteria, and those who are gluten intolerant may be able to drink them without ill effect. This depends on individual sensitivity, as each person displays a different level at which an autoimmune response will be activated. As such, there is ongoing debate about acceptable gluten "levels" to celiacs.
Consumers of "low gluten" beverages are advised to inform the consultants of their diet, and to ensure that even if the obvious symptoms are absent, there are no hidden negative effects from peptides in the beer. Some brewers suggest that their low barley malt beers are not dangerous to celiacs, but not all evidence supports this. There are brewery statements that "normal beverages" such as Budweiser are safe, tempered with advice that they should be drunk with caution. Donald D. Kasarda, a research chemist with the United States Department of Agriculture, says that: "It is not proved beyond any doubt that the peptides in beer are actually toxic to celiac patients, but it is quite possible that the peptides remaining in any barley-based or wheat-based beer ... are harmful to celiac patients." 
According to tests done by the Argentine Coeliac Association (ACELA) and the Swedish National Food Agency, Corona beer, contains less than 20 ppm, making it legally gluten-free. This is probably due to the fact that Corona, like most pale lagers, contains rice and/or corn in addition to malted barley. Corona has made no statement regarding these tests.
The recent development of gluten-free ales and lagers has been seen as a positive move forward for those who suffer a variety of related gluten intolerant conditions; and there are a number of people working to produce gluten-free beer.  Of gluten-free products, beer is seen as the most difficult to produce in a commercially acceptable version. As of early 2012, a fast-growing range of ales and lagers is becoming widely available.
Formulas for home brewing gluten-free beer can now be found. Many of these include a sweet sorghum syrup as the principal carbohydrate. This is commercially manufactured from sorghum grain to be a malt substitute and contains amino acids and unfermentable sugars needed for yeast nutrition and "mouth feel". Other sugars can be added for character and "feel", such as honey and maltodextrin, and roasted or malted buckwheat.
Gluten Free home brewing is now easy with commercially available gluten free home brewing kits containing the sorghum syrup, hops, yeast and other items. The cost of the kits, while more expensive than standard home brew kits, still produce very drinkable GF beer for less than the cost of a standard commercial beer. Many find the taste of GF beers to be missing something. Adding additional hops has been found to improve flavour greatly.
Gluten-free beer festivals
The first international gluten-free beer festival was held in February 2006 in Chesterfield, United Kingdom, as a joint enterprise between the Campaign for Real Ale (CAMRA). However, with new brews being created around the world, particularly in the UK and the USA, there is a worldwide movement towards this return to a 'normal' life.
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- Media related to Gluten-free beer at Wikimedia Commons