Wort composition

The nature of the materials and procedures used to make wort make it inevitable that its composition is complex and, in fact, not well characterised. Thus, Hudson (1973) described the single condition that wort composition must meet as that which pro duces a beer of desired character by intention rather than by chance. It is perhaps implicit in this definition that it is not necessary to know the precise composition as long as the materials and methods used in its preparation are themselves constant. Many of the components are of little relevance to the processes which occur during fermentation in that they take no active role. However, they may contribute to beer flavour, aroma and colour.

Wort composition is influenced by the nature of the raw materials and management of the processes used in its preparation. With regard to the raw materials, the nature of the brewing water, the blend and addition rate of hops, the blend and types of malt and the nature of any adjunct are all influential. The latter is of special relevance in that whereas all-malt wort will tend to produce wort with an appropriate balance between fermentable sugar and amino nitrogen, use of high concentrations of sugar adjuncts will have an obvious impact on carbon to nitrogen ratios.

During wort preparation, the conditions of mashing and boiling are of particular significance. Low mashing temperatures favour continued activity of heat-labile malt proteases and therefore elevated concentrations of amino nitrogen are formed. Conversely, higher mashing temperatures favour amylolytic activity at the expense of proteolysis and in consequence the ratio of fermentable sugar to amino nitrogen increases. In addition, the relative activities at different mashing temperatures of a-and p-amylases and limit dextrinase will modulate the sugar spectrum of wort. Furthermore, the method of separation of sweet wort from spent grains and conditions of the boil all influence the precise composition of wort in fermenter.

Wort is a clear liquid, which usually contains a small proportion of suspended trub. The requirement for wort clarity is somewhat controversial. This parameter is often used as a measure of wort quality and the performance of the brewhouse may be judged on the basis of its ability to generate bright wort with a very low trub content. However, others (Olsen, 1981; Schisler et al., 1982; Lentini et al., 1994) argue that some trub is needed during fermentation as a source of lipids (especially unsaturated fatty acids) which are essential to yeast nutrition. Second it has been suggested that trub can provide nucleation sites to assist carbon dioxide bubble formation and breakout (Siebert et al., 1986). The common sense answer is that the individual brewer operates the brewhouse in such a way as to produce wort that gives satisfactory fermentation performance. It is a matter of fact that solids must be removed at some stage in the process between wort production and beer packaging. It is perhaps less important where this is actually achieved and there are obviously advantages and disadvantages whichever choice is made. It may be of practical relevance, however, where new plant is installed which significantly changes wort clarity. In this case changes in fermentation performance may be observed which require corrective action such as a change in yeast pitching rate and/or wort oxygenation regimes.

Worts of specific gravity within the range 1.03-1.06 (7.5-15°Plato) contain approximately 7.5-15% dissolved solids. Wort pH is typically in the range pH 5.05.3. The colour is highly dependent on the materials used for production and varies between a very pale brown through to almost black. Wort viscosity is dependent on the total solids content and the concentration of components such as (3-glucans derived from malt. Typical values for worts of 7.5-25°Plato are 1.6-5.0 cP (Hudson, 1970). Wort dissolved solids comprise approximately 90-92% carbohydrate and 4-

5% nitrogenous components (MacWilliam, 1968). The remainder consists of a wide variety of organic compounds which encompass all the major groups of biochemicals which would predictably be extracted from a living cell and withstand the conditions which pertain during wort preparation.

2.4.1 Carbohydrates

Maltose is the most abundant sugar, usually accounting for 60-65% of the total fermentable sugar. The remainder consists mainly of glucose, fructose, sucrose, maltotriose, maltotetrose and higher dextrins (MacWilliam, 1968; Enevoldsen, 1974; Hoekstra, 1974; Kieninger & Rottger, 1974; Taylor, 1974). Carbohydrate spectra of some typical worts are shown in Table 2.3. Some of the variations in sugar spectra due to different wort production procedures are summarised in Table 2.4.

Table 2.3 Carbohydrate composition of worts (g 100 ml ') (from MacWilliam, 1968).







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