are commercially sold by companies such as Soda-Club; dry ingredients are often sold in pouches, in a style of the popular U.S. drink mix Kool-Aid. Carbonated water is made using a soda siphon or a home carbonation system or by dropping dry ice into water. Food-grade carbon dioxide, used for carbonating drinks, often comes from ammonia plants. Drinks like ginger ale and root beer are often brewed using yeast to cause carbonation. Of most importance is that the ingredient meets the agreed specification on all major parameters. This is not only the functional parameter (in other words, the level of the major constituent), but the level of impurities, the microbiological status, and physical parameters such as color, particle size, etc. Some soft drinks contain measurable amounts of alcohol. In some older preparations, this resulted from natural fermentation used to build the carbonation. In the United States, soft drinks (as well as other products such as non-alcoholic beer) are allowed by law to contain up to 0.5% alcohol by volume. Modern drinks introduce carbon dioxide for carbonation, but there is some speculation that alcohol might result from fermentation of sugars in a non-sterile environment. A small amount of alcohol is introduced in some soft drinks where alcohol is used in the preparation of the flavoring extracts such as vanilla extract. Producers Market control of the soft drink industry varies on a country-by-country basis. However, PepsiCo and the Coca-Cola Company remain the two largest producers of soft drinks in most regions of the world. In North America, Keurig Dr Pepper and Jones Soda also hold a significant amount of market share. Health concerns The over-consumption of sugar-sweetened soft drinks is associated with obesity, hypertension, type 2 diabetes, dental caries, and low nutrient levels. A few experimental studies reported the role sugar-sweetened soft drinks potentially contribute to these ailments, though other studies show conflicting information. According to a 2013 systematic review of systematic reviews, 83.3% of the systematic reviews without reported conflict of interest concluded that sugar-sweetened soft drinks consumption could be a potential risk factor for weight gain. Obesity and weight-related diseases From 1977 to 2002, Americans doubled their consumption of sweetened beverages—a trend that was paralleled by doubling the prevalence of obesity. The consumption of sugar-sweetened beverages is associated with weight and obesity, and changes in consumption can help predict changes in weight. The consumption of sugar-sweetened soft drinks can also