Varietal Differences

The influence of variety on the performance of a hop in brewing will be determined by both quantitative and qualitative considerations. Traditionally, varieties were selected on the basis of their aroma properties and tended to be of low bittering potential, containing rarely more than 4% alpha-acids. Despite their low essential oil content, c, 0.5%, these hops were used in sufficient quantity to achieve the desired bitterness level in the beer. This in turn meant that an adequate amount of the important hop oil components was present as well. 

In the main, varieties differ in the relative proportions of the compounds present in the oil rather than in the possession of unique components. A variety or blend of varieties will have been chosen for the particular balance that it brings to the beer, while maintaining the required bitterness. 

With the introduction of the bitter varieties containing over 10% of alpha acids, coupled with a downward trend in bitterness levels in beer, the total amount of hop material added to beer has declined. Although these varieties contain higher concentrations of essential oil, 0.8- 1.5%, the proportion of hydrocarbons is higher and the positive contribution to aroma and flavour is often inadequate. The efficient use of aroma varieties to complement the bitter varieties is one of the objectives of hop processing. It follows that methods must be chosen that retain the varietal characteristics of the raw material. 

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Figure 1. Varietal Differences in Raspberries as Indicated by Transmittance of Centrifuged Juices...

Even a moderate quantity of salt reaching the leaves has a drastic effect on photosynthesis and leaf ultrastructure, much more than could be accounted for by the average tissue concentration (Flowers etal., 1985). Salt may accumulate in the apoplast (because it is not taken up fast enough by the cells of the leaf), and this would result in severe localised water deficit (Oertli, 1968). Differences in apoplast/protoplast balance are thought to be responsible for varietal differences in tissue salt load which can be accommodated (tissue tolerance Yeo Flowers, 1986). The xylem concentration of Na" is very much lower to young leaves than to older leaves (Yeo et al., 1985). This is advantageous in salt resistance because it means that at least some leaves are protected from salt, which otherwise causes premature leaf death (Yeo Flowers, 1984 Fig. 2). 

Varietal differences exist in all of these characteristics, and it is our theory that parents conferring the required traits should be combined. Depending on heritability and combining ability, we may add together genes for a number of useful characteristics, and a variety more resistant than any which has arisen by chance should be produced. Salt resistance is thus... 

Varietal differences with regard to the amount of DDT present in the peel of harvested fruits sprayed at different times during the development of the fruit suggest the... 

Ekgorg-Ott, K.H., Taylor, A., Armstrong, D.W. (1997). Varietal differences in the total and enantiomeric composition of theanine in tea. J. Agric. Food. Chem. 45, 353-363. 

Axberg K, Jansson G, Svensson G and Hult K (1997), Varietal differences in accumulation of ochratoxin Ain barley and wheat cultivars after inoculation of Penicillium verrucosum, Acta Agric. Scand., 47, 229-237. 

Yang J, Meyers KJ, van der Heide J and Liu RH. 2004. Varietal differences in phenolic content and antioxidant and antiproliferative activities of onions. J Agric Food Chem 52 6787-6793. 

Although most consumers appreciate the fieriness of chile, capsaicinoids are not perceived through odor or taste receptors but through the nociceptive pain receptors described earlier. The compounds in chile fruit that create the flavor and aroma are produced in the fruit wall. Buttery et al. [90] generated vacuum steam distilled oil from green bell pepper macerate, with well over 40 peaks on subsequent GC/MS analysis. Of these peaks, the major flavor compound associated with bell pepper aroma was 2-methoxy-3-isobutylpyrazine (Fig. 8.1). They also reported several monoterpenoids in abundance, limonene, trans- 3-ocimene, and linalool as well as other aliphatic aldehydes and ketones. The flavor composition of dried red bell pepper powder (sweet paprika) extracted with ether identified 44 key peaks by GC/MS [91]. In these dried samples the key compounds were P-ionone and several furanones. The post-harvest processing and the different fruit maturities as well as possible varietal differences are all causes for the different aromatic profiles. 

Duncan, B. (1992). Varietal differences in white grape protein Implications for bentonite fining. Aus. New Zealand Wine Ind.. 7,189-193. 

Appreciable delay of ripening and consequent enhancement of shelf life have been noted in some tropical fruits such as bananas, plantain, and mangoes after low-dose irradiation (0.2-0.7 kGy) [40,41]. Maximum delay of ripening has been observed with fruits of lower maturity. However, these feasible levels of doses are close to those that induce phytotoxicity, and many factors (varietal differences, the fruit s stage of maturity at the time of irradiation, etc.) make the outcome of the treatment uncertain. 

Bilyk, A. and Sapers, G.M., Varietal differences in the quercetin, kaempferol, and myricetin contents of highbush blueberry, cranberry, and thornless blackberry fruits, J. Agric. Food Chem., 34, 585, 1986. 

Cantos, E., Espin, J., and Tomas-Barberan, F., Varietal differences among the polyphenol profiles of seven table grape cultivars studied by LC-DAD-MS-MS. J. Agric. Food Chem. 50, 5691, 2002. 

Somers, T.C. and Pocock, K.F., Phenolic assessment of white musts varietal differences in free-run juices and pressings. Vitis 30, 189, 1991. 

Buyken and Kroke (2005) have summarized some reasons why a conclusion that all potatoes have a high GI is unjustified, pointing out the sometimes tenuous evidence for varietal differences, effects of maturity, and effects of processing as well as the effects of food consumption habits, all of which are discussed below. 

GB Nickerson, PA Williams. Varietal differences in the proportions of cohumulone, adhumulone, and humulone in hops. J Am Soc Brew Chem 44 91-94, 1986. 

Variety. Frequently extreme differences are found in the response of species or varieties to irradiation. Irradiated Southland peaches tend to become somewhat mealy following irradiation, but the Loring and Dixieland varieties do not. Valencia oranges show considerable peel injury from irradiation but not Pineapple oranges. However, this could be more of a seasonal response than a varietal difference. 

Nutman, P.S. (1967). Varietal differences in the nodulation of subterranean clover. Aust. J. Agric. Res. 18, 381-425. 

Malleshi, N. G. and Desikachar, H. S. R. (1981b). Varietal differences in puffing quality of ragi (Eleusine coracana). J. Food Sci. Technol. 18,30-32. 

Stone, P.J., Nicholas, M.E. 1996. Varietal differences in mature protein composition of wheat resulted from different rates of polymer accumulation during grain filling. Aust J Plant Physiol 23 727-737. 

Little needs to be said of these. They are predominantly of the sherry and port types, and the nature of these types is determined more by fabricating procedure than by the grapes used—though varietal differences are still important in the finer grades. 

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