Gluten-free beer: How is it made, how is its gluten content tested, and is it really safe for coeliacs?
Sue Cane investigates.
Beer made from barley has always been out of bounds for coeliacs but now there are products on the shelves which are certified gluten-free. How can beer made from barley malt be safe and, if this is the case, does it follow that ordinary beer might be gluten-free?
Testing for gluten – the sandwich and the competitive
The preferred method of testing for gluten in food is the ‘enzyme-linked-immunosorbent assay’ (ELISA), which uses antibodies to detect the components of gluten protein. In this type of test tiny fragments of gluten bind with gluten antibody, rather like the way a lock and key fit together. The more fragmented and damaged the gluten molecules become during processing (1) (2), the less well they fit with the antibody, and during fermentation they become particularly degraded.
The two main assays used are the ‘direct’ and’ indirect’ methods, known as the ‘sandwich’ and ‘competitive’ ELISA. As Phil Goodwin at Imutset explains, the former uses a sandwich of two gluten antibodies to bind to the sample of captured antigen (gluten) which has to be large enough and sufficiently undamaged to provide two epitopes, or binding sites. The latter ‘competitive’ method, much used by the brewing industry, uses the second of the 2 antibodies used in the ‘sandwich’ method, but this time smaller gluten fragments with as little as one epitope have an effect and can be counted. This method has been shown to be better at identifying small fragments of gluten (3) (4).
The difficulties of testing beer for gluten
Marc Burke of Neogen, clearly explains the difficulties involved in testing beer and why the competitive ELISA is currently the recommended assay.
‘Heating and fermenting hydrolyses proteins. If you think of a globular structure in the shape of a football, at the end of the process it won’t look like a football. It may look like a rugby ball or it may fragment into many different tennis ball shapes, but there’s no knowing what it will look like. The competitive assay looks for smaller molecules, smaller areas and people in the industry recommend it because they believe it’s got a better chance of picking up any hydrolysed proteins that are there.’
Of the ELISAs, most people use one of two antibodies, known as Skerritt and R5 (5), to react with the gluten. These are both available in many different test kits and although the European Commission has made an attempt to standardise the testing procedure (6), it is unfortunate that there is no requirement on food producers to use exactly the same ones. Indeed the dominant antibody, the R5, is licensed for use by only a few companies.
The Skerritt and R5 antibodies were developed against prolamins (seed proteins of wheat, barley and rye) but each have different affinities with wheat and barley which affect their ability to detect them. These differences in binding affinity (i.e. how well they can identify and attach themselves to different fragments of gluten) persist in the commercially available kits and may actually affect their detection of gluten in foods (5) (3) (4).
Lack of accepted reference standard
Clearly the lack of an accepted reference standard for testing allows the discrepancies that exist between different methods to influence their results (5) (1), something that both analysts and the regulatory community acknowledge (7). In addition, more work is needed to assess the suitability of these tests for ‘processed food and complex food matrixes’ such as beer, where the gluten has been radically altered by processing (2) (13). The fact that most methods of analysis are based on the particular characteristics of the most soluble part of wheat protein, gliadin (4) also means that they cannot be used with accuracy on barley. Unfortunately little research has been done into the specific toxicity of hordein (8).
'The presence of gluten it is not an absolute indicator of toxicity in food for coeliacs.'
Although testing does give us a measure of the presence of gluten it is not an absolute indicator of toxicity in food for coeliacs (4). This is difficult to quantify, and as Phil Goodwin says, ‘the assay results are markers of the presence of gluten rather than measures of the likelihood of a food to cause harm. You can’t prove the negative i.e. no fragments left’.
‘The molecular modifications used on gluten in food processing are often similar to those that occur during digestion in the intestine, she says. ‘Hydrolysis is caused by proteinases in the intestine. Breaking gluten into fragments certainly should not be viewed as a way of making it safe for CD patients because it is small fragments of gluten that cause the damage.’
Sensitivity variability and the need for a safe threshold
We do know that gluten sensitivity varies greatly between individuals and that there is a need to establish a safe threshold which takes this into account (9) (10). The new 20ppm (6) limit is helpful in keeping coeliacs’ intake of special foods to below the recommended safe limit of 50mg/d, but as Phil Goodwin’s figures show, the consumption of 2 litres of beer at 6ppm is already quarter of this daily amount (6mg/kg x 2kg = 12mg gluten). It is clearly easy to achieve possibly detrimental levels of gluten from the high-volume consumption associated with certain foods, even though they are described as gluten–free.
But if brewing does break down barley protein into small fragments which are below safe limits, does that mean that even ordinary beer is safe to drink? The answer is that we don’t know unless it’s been tested. Certainly none of the gluten-free beers on the market contain wheat, which is present in most ordinary beer. Results of tests published in Sweden (14) show varying levels of gluten from low single-figures in some brands to the high thousands in others. Given the complexity of the lab-based ELISAs needed for the most accurate tests, it will be some time before we can easily perform these at home. And seeing that the potential toxicity to coeliacs of trace amount of gluten is still unclear (9) (4) it makes no sense at all to take these risks.
The Independent published a guide to gluten free beers around the world in October 2010 which readers might like to check out.
First published in January 2011