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Dealing with Dextrins

28th Nov 2017 by Richard

Beer is often said to have body but what makes a beer watery? An obvious answer is simple H2O. A feature which beer has in abundance. Generally over 90% of your pint is water with the remainder a mixture of protein, carbohydrate, salts and flavourings including, of course, ethanol.

Perhaps a better question is what features give beer body? And - which features can you control to achieve a specific body to your beer?

The answer to this is less obvious as all manner of things may contribute to the impression of body: protein, unfermented sugars, hops, alcohol, polysaccharides and, perhaps, tannins. Even colour seems to influence the perception of body with dark beers often judged stronger and thicker.

Body is the characteristic feature resulting from the components listed above and is an additional target on your recipe listing. A beer’s body will be somewhere in the range from watery, through light, solid, grainy and creamy to thick and cloying. Crafting this characteristic can be a challenge and may vary for a number of reasons, not all of which are easy to control such as inconsistency of ingredients.

Beers with few of the components listed above will have a watery body - limited thickness on the tongue, limited retention in the mouth and low viscosity. Such beers have a refreshing character. They are often of low original gravity generally hoppy and bright, typically lager-like and highly carbonated.

Thicker beers differ considerably. These linger longer in the mouth producing a creamy smoothness and solid mouthfeel. They have a high viscosity, are often stronger and with a high finishing gravity. They are also the more challenging beers to brew and control.

The body of a beer results particularly from the presence of proteins and large, unfermentable sugars called dextrins released during mashing. Alcohol may also contribute. These components produce a viscous solution which contributes to the elevated gravity of a fermented beer. Without them beer would be as dry and as low in gravity as wine.

A simple viscosity effect may be enough to account for much of the body of a beer. Dextrin levels contribute significantly to this and their level may be adjusted by controlling the temperature of your mash.

Low temperatures (below 65oC) and low pH levels (pH 5.2) are more conducive to a full starch digestion. Higher temperatures, over 65oC, are more likely to leave significant levels of incompletely digested starch. These dextrin molecules pass through the boil with little further change. They are too large to be fermented and so become a major component of the final beer.

Body does not necessarily correlate with bitterness or with astringency. Such features contribute independently to mouthfeel and may balance the smoothness of a thick beer. They also persist in the aftertaste after the beer drains down the throat so creating aftertaste.

Mouthfeel is certainly not just the body of a beer but a much more variable feature. Thickness contributes strongly to mouthfeel but so can dryness, astringency, metallic character and the tingle of carbonation. Body and thickness are, however, major features of mouthfeel which has been defined as “those textural attributes responsible for producing tactile sensations”.

Additional factors may occur in some conditions. High gravity fermentations, for example, produce glycerol which has a significant impact on mouthfeel. Adding sulphite salts, or having high sulphite levels during fermentation will also enhance the level of glycerol. Wine is typically smoothened by glycerol which may give high alcohol beers a vinous character.

Proteins and tannins from malt are a further contributor to mouthfeel. Your choice of malt, particularly the extent of its modification, may even be a factor and cause variability if you change sources regularly. Low tannin malt is sometimes used to limit the level of tannins and so create a less aggressive beer.

Finally the degree of sweetness is particularly relevant. Although dextrins aren’t particularly sweet some residual fermentable sugars will be and will provide a changing impression as they ferment in cask. Moreover, other components such as hop bitterness and tannins will act to balance sweetness and neutralise its effect.

With all these factors in the running is there a way to anticipate the effect of mouthfeel in your beer? Mashing at a range of temperatures is an unlikely experiment on a commercial level. Adding purified dextrins has been attempted but requires very high levels to really thicken a beer, almost as much as you would need to convert it to gravy.

A viscometer may be a useful tool to provide an objective measure of your beer’s thickness but requires an amount of laboratory support to operate. Keeping a careful note of your degree of fermentation, your final gravities and perceived mouthfeel and body is perhaps the best empirical approach.

Either way building a log of beer thickness will help you anticipate and plan for matching your target recipe. Yet another feature to include on your growing list of beer analyses.

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