Several wort components can chelate metal ions. Should the metal chelates be insoluble there is an opportunity for the ions to be lost during wort production and thereby produce deficiencies in fermenter. For example, zinc ions may bind to amino acids and calcium ions to polyphenols (Jacobsen & Lie, 1977). Since a proportion of wort amino acids (as polypeptides or protein) and polyphenols are removed as hot and cold break during wort boiling and cooling, a fraction of the bound metal ions may also be lost. This possibility has been confirmed in the case of zinc (Daveloose, 1987) and many brewers add this metal to wort in fermenter before pitching.

Several authors have reported that worts may be deficient in magnesium ions, for example, Dombek and Ingram (1986b); Walker et al. (1996); Rees and Stewart (1997). The latter reports concluded that the relative concentrations of calcium and magnesium could be important and that very high ratios of calcium and magnesium could exert detrimental effects during fermentation by reducing the availability of magnesium to yeast. These observations appear not be of universal applicability, presumably indicating considerable variation in metal contents of worts, or use of yeast strains with differing metal ion requirements. Thus, Bromberg et al. (1997) found no effect on any fermentation parameters when a 16°Plato wort was supplemented with manganese (five-fold), magnesium or calcium (two-fold) or by varying the magnesium-calcium ratio from one to four. Only addition of zinc (0.1-0.15 mgl *) was found to stimulate fermentation rate, but not yeast growth.

2.4.7 Miscellaneous

A few of the other myriad components of wort are worthy of brief mention. Beer contains considerable quantities of simple organic acids. Most of these arise during fermentation as the result of yeast metabolism; however, small concentrations are present in unpitched wort. Mandl (1974) reported that in a 12°Plato wort, citrate was the most abundant organic acid at 170 mg 1 l, followed by gluconate and malate at 50 and 60 mgl l, respectively. Pyruvate, D-lactate and L-lactate were present at concentrations of less than 10 mgl 1. In addition, MacWilliam (1968) reported the presence of small quantities (approximately 10 mgl *) succinate, fumarate, oxalate and a-ketoglutarate.

Vitamin contents of worts are (|igl *); thiamine, 150-750; pyridoxin, 150-200; p-aminobenzoic acids, 20-50; nicotinic acid, 1500-2500; inositol, 40000^15 000; pantothenate, 150-250; biotin, 5-10; riboflavin, 300-500 and folic acid, 50-100 (MacWilliam, 1968; Graham et ai, 1970; Silhankova, 1985).

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