Low- or non-alcoholic beers were first produced in the United States more than eighty years ago (during Prohibition), and have been available ever since. However, the relatively low demand for these products did not drive the industry to devote very much research effort into new technologies. Due to a marked increase in the consumer demand for low- or non-alcohol products, the technology for making these beers has improved dramatically in the last decade.The quality of these beers, not surprisingly, has also improved (although there are still many detractors who would argue otherwise), as has the availability of many different domestic and imported products.
Non-alcoholic beers must contain less than 0.5% ethanol. Historically, several different processes have been used to produce nonalcoholic beer. The earliest methods generally involved removing the ethanol from normal beer by evaporation or distillation. Although these methods are still used, various filtration configurations, in particular, dialysis and reverse osmosis, are now more widely used. Beer quality is arguably much better by the latter processes because they operate at low temperatures (<10°C) and the heat-generated reactions that affect flavor do not occur.
In reverse osmosis systems, the beer is pumped or circulated at high pressure (more than 5,000 Pascals) through small pore membranes with average molecular weight cutoffs of less than 0.01 ^m.The ethanol molecules pass through the membrane as part of the permeate, along with a portion of the water. The retentate contains nearly all of the beer solids and most of the water, but little or none of the ethanol. Water can either be added back to its normal level, or the beer can be diluted beforehand to account for the water lost from the retentate. Dialysis operates in a similar manner, except that the driving force is simply the concentration difference across the membrane. Despite the less intrusive nature of these processes, however, flavor compounds may still be lost.
Another entirely different way to make these beers relies not on ethanol removal, but rather on modifying the fermentation so that ethanol is not made as an end product.The fermentation can simply be abbreviated, such that yeast growth is stopped or curtailed before much ethanol has been produced. Alternatively, the fermentation can be conducted at a low temperature (<5°C) that restricts yeast growth and ethanol formation. However, these methods may result in a beer that is too sweet and microbiologically unstable, due to high levels of residual sugars. Modifying the wort composition by removing fermentable sugars prior to fermentation is another way to limit ethanol production. Finally, metabolic engineering of the yeast, such that the ethanol pathway is blocked, may be an ideal way to reduce the ethanol content in beer, but without leaving behind fermentable sugars (Box 9-9).
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