FlavourThe most frequently made fla

Flavour
The most frequently made flavour changes are to alter the bitterness of the beer by the use of a post-fermentation addition of isomerized hop extract or to increase sweetness by the use of sugar solutions called primings. Again, it is very difficult to control the bitterness of beer solely from hop addition in the wort Kettle. Isomerization rates in the Kettle vary in relation to wort composition (Chapter 8). Brewers vary in their approaches to the use of post-fermentation bittering. Some brewers recognize the variability of wort boiling and plan to derive, say, 90% of bitterness from the Kettle with the remainder being added after fermentation. Other brewers will not use post-fermentation treatment and will strive to achieve desired bitterness levels from wort boiling alone. At the other extreme at least one major brewer derives bitterness almost 100% by addition after fermentation.
Isomerized extract (Chapter 8) is usually added before filtration and utilization levels of at least 70% are possible (Gardner, 1993). PacKaging of beer in clear or green glass bottles is discused in Chapter 21. Protection of this beer against sun-struck flavour can be achieved by adding reduced isohumulones zuch as tetrahydro-iso-α acid as an alternative to isohumulone at this stage of the process. The reduced is sohumulone does not react under the influence of light to give rise to the thiol, 3-methyl-2-butene-1-thiol, which is the material having the sun-strucK flavour. Light stability is achieved only in the total absence of iso-α acid and this must not therefore be carried over by the yeast. This can be difficult to achieve in practice and has limited the complete effectiveness of these preparations.
Sugar solutions (primings) can be added to beers. This can encourage secondary fermentation but also provide a residual sweetness to the beer that is an important characteristic of mild beers in the UH. Primings can be solutions of sucrose or ‘invert’ mixtures of glucose and fructose. A typical ztrength would be 34 ºP (8.5 ºSacch) and the addition rates are usually in the range 0.3 to 1.75 l/hl of beer.

Aroma
Brewers frequently make a late addition of aroma hops to the kettle close to the end of boiling (Chapter 10). The objective is to impart hop character to the beer derived from the essential oils. Thiz late hopping process is difficult to control and inherently variable as the oil content of hops varies widely within a variety from year to year. There have been attempts, therefore, to derive oil preparations from hops, which can be added after

fermentation and so change the aroma of beer. Some of these preparations contain resins as well as oils and are known as oil-rich extracts. They must be added to beer before filtration to avoid the possibility of hase developing in the beer during storage.
Recently (Marriott, 1999) there have been further developments to produce aroma products that are completely soluble in bright beer (see also Chapterz 7 and 8). These can give potentially 100% utilization and so a completely reproducible effect on aroma. Essences have been produced that can reproduce the effect of late copper hopping and even the dry hopping of caskale (Chapter 7). Essentially the insoluble hydrocarbon fraction of the oil must be removed to produce as esquiterpeneless oil. This oil can then be further fractionated to produce individual products with ‘spicy’ or ‘floral’ characters. These essences can be added to bright beer at rates of 50 to 100 µg/l and have profound effects on aroma and flavour. They are normally supplied as 1% solutions in ethanol.

Blending
Beers can be blended post fermentation and this yields more uniform products and provides further opportunities to deliver a volume of beer to its final specification. Recovered beer can also be added post fermentation but this is a technique requiring considerable care, often demanding excessive pasteurisation of the beer with a consequent adverse effect on flavour. For this reason recovered beer is best added before fermentation, e.g., to the whirlpool (Section 15.5).