(((reprinted from The Truth About Garden Remedies- credited above)))
Beer as a fertilizer- "Beer is usually recommended for the lawn, but it is also recommended for the vegetable or flower garden. Recommendations are usually for about a tablespoon of beer added to every gallon of water, but they can include concentrations of up to a full can of beer, undiluted, for a small yard area.
...Beer contains water, carbon dioxide, ethanol (the alcohol that inebriates us), a wide variety of carbohydrates (sugars) that make the beer taste good, a small quantity of protein (which contains nitrogen), and a few other things, such as trace elements, in very small quantities.
...Carbon dioxide is unlikely to have an effect on the plant, as there is substantial carbon dioxide in the air. Ethanol is not helpful to plant growth; in fact, ethanol can be quite detrimental, causing plant burn and even death. That leaves us with carbohydrates and protein. Various carbohydrates, also known as sugars, have been shown to be taken up by the roots of plants (Begna et al. 2002; Saftner and Wyse 1984). Carbohydrates are the building blocks of plants, so these additional carbohydrates could help, but protein is more likely the answer as to why beer might increase plant growth and health. Beer contains about 6 grams of protein in every liter (about 1/4 gallon), which, while not a huge amount, could certainly be helpful if no other source of nitrogen is available. Besides the protein, other nutrients your plants need are present in beer, such as iron, copper and zinc (Wyrzykowska et al. 2001), but the concentration of these are probably two low to help plant growth much unless they are completely absent in the soil. So beer does contain some nutrients that could help plant growth, but it also contains ethanol, which should inhibit plant growth."
