Taste coffee

Lindinger, C., Labbe, D., Pollien, P, Rytz, A., Juillerat, M.A.,Yeretzian,C.,Blank,I. (2008) When machine tastes coffee instrumental approach to predict the sensory profile of espresso coffee. Analytical Chemistry, 80, 1574-1581. 

Lindinger, C., Yeretzian, C., Blank, I. (2009) When machine tastes coffee successful prediction of coffee sensory profiles by instrumental methods based on on-line PTR-... 

C8H10N4O2. An alkaloid occurring in tea, coffee and guarana, from which it may be prepared by extraction, It is also manufactured by the methylation of theobromine and by the condensation of cyanoacetic acid with urea. Crystallizes with H2O or anhydrous from organic solvents. M.p. (anhydrous) 235"C, sublimes at 176 C. Odourless, and with a very bitter taste. Caffeine acts as a stimulant and diuretic, and is a constituent of cola drinks, tea and coffee. 

Lactisole [13794-15-5] the sodium salt of racemic 2(4-methoxyphenoxy)propionic acid, is a sweet-taste inhibitor marketed by Domino Sugar. It was affirmed as a GRAS flavor (FEMA no. 3773). At a concentration of 100 to 150 ppm, lactisole strongly reduces or eliminates the sweet taste of a 10% sugar solution. This inhibition appears to be receptor-related because lactisole also inhibits the sweet taste of aspartame. The 5 -( —)-enantiomer [4276-74-8] (38), isolated from roasted coffee beans, is the active isomer the i -(+)-enantiomer is inert (127). 

The paper describes the different chemical sensors and mathematical methods applied and presents the review of electronic tongue application for quantitative analysis (heavy metals and other impurities in river water, uranium in former mines, metal impurities in exhaust gases, ets) and for classification and taste determination of some beverages (coffee, bear, juice, wines), vegetable oil, milk, etc. [1]. 

How would you describe the differences between a cup of coffee and a cup of hot water What probably come to mind are the aroma, the dark color, and the taste of a good cup of coffee. Coffee s action as a stimulant is another obvious difference. These properties come from the chemical compounds that hot water dissolves from ground coffee beans. These compounds are molecules constructed from different atoms bound together in veiy specific arrangements. The molecule that makes coffee a stimulant is caffeine. Our background photo is a magnification of crystals of pure caffeine, and the inset is a ball-and-stick model of this molecule. 

The molecules of a molecular solid retain their individual properties. Solid I2, for example, is dark in color because individual I2 molecules absorb visible light, as shown by the fact that I2 vapor also is colored. Glucose dissolved in coffee tastes just as sweet as solid glucose because the sweet taste of glucose comes from its shape, which is the same in the solid phase as it is in solution. 

Roast style is a matter of personal taste, but for the most part the mildest Arabica coffees are the lightest roasted. Some Arabica coffees even become bitter if they are roasted to too high a temperature. Dry-processed Robustas and Brazilian Arabicas, on the other hand, benefit from deeper roasting. 

The coffee beans with the most desirable flavor to many tastes are the highest grown Arabicas prepared by the wet method. Coffee beverages need to be prepared within 8 h of grinding the freshly roasted coffee beans if the volatile flavor and aroma compounds are to be retained. Brew... 

The coffees commanding the highest prices are also those with the most desirable taste quality. An order of decreasing value for some coffees follows wet-processed high-grown and then low-grown Arabicas, followed by dry-processed Arabicas and Robustas. Blends are made, in general, to reduce the cost. 

If the instant coffee has been spray-dried, then the brew colloids will have been broken down and the beverage will have lost some of its smoothness . The generally mild taste of instant coffees is usually offset... 

Several of the lower molecular weight aliphatic compounds, in a mixture, are part of the roasted coffee aroma. A nine-compound mixture with roasted coffee aroma contained isopentane, n-hexane, acetaldehyde, dimethyl sulfide, propanal, isobutanal, isopentanal, methanol, and 2-methylfuran.20 In addition, the freshness of aroma and taste has been correlated with 2-methylpropanal and diacetyl. When the concentration of these falls off, so does the taste.21 Other aliphatic compounds that are steadily lost from ground roasted coffee, unless it is vacuum packaged, include methyl formate, methyl acetate, methyl thioacetate, and acetone.22 The concentrations in roast coffee for four compounds whose contribution to the fresh flavor have long been known are dimethyl sulfide (4 ppm), methyl formate (12 ppm), isobutanal (20 ppm), and diacetyl (40 ppm). The taste thresholds are 0.1, 0.5, 0.5, and 1.0 ppm, respectively, in the brew made with 5 g coffee per 100 ml water.15... 

Anon., Composition for improving the taste of coffee, Neth. Appl. 74 08,455, 1975.(CA85 107677h)... 

Alkaloids are compounds that contain nitrogen in a heterocyclic ring and are commonly found in about 15-20% of all vascular plants. Alkaloids are subclassified on the basis of the chemical type of their nitrogen-containing ring. They are formed as secondary metabolites from amino acids and usually present a bitter taste accompanied by toxicity that should help to repel insects and herbivores. Alkaloids are found in seeds, leaves, and roots of plants such as coffee beans, guarana seeds, cocoa beans, mate tea leaves, peppermint leaves, coca leaves, and many other plant sources. The most common alkaloids are caffeine, theophylline, nicotine, codeine, and indole... 

Water is a good choice of solvent in a standard kitchen percolator because it removes all the water-soluble components from the coffee - hence the flavour. Clearly, however, a different solvent is required if only the caffeine is to be removed. Such a solvent must be cheap, have a low boiling point to prevent charring of the coffee and, most importantly, should leave no toxic residues. The presence of any residue would be unsatisfactory to a customer, since it would almost certainly leave a taste and there are also health and safety implications when residues persist. 

The preferred solvent is supercritical CO2. The reasons for this choice are many and various. Firstly, the CO2 is not hot (CO2 first becomes critical at 31 °C and 73 atm pressure see Figure 5.5), so no charring of the coffee occurs during decaffeination. Furthermore, at such a low temperature, all the components within the coffee that impart the flavour and aroma remain within the solid coffee - try soaking coffee beans in cold water and see how the water tastes afterwards Caffeine is removed while retaining a full flavour. 

Secondly, solid CO2 is relatively cheap. Finally, after caffeine removal, any occluded CO2 will vaporize from the coffee without the need to heat it or employ expensive vacuum technology. Again, we retain the volatile essential oils of the coffee. Even if some CO2 were to persist within the coffee granules, it is chemically inert, has no taste and would be released rapidly as soon as boiling water was added to the solid, decaffeinated coffee. 

The question of conditioning one s taste is a matter which needs to be considered in this connection. Because it has been repeatedly observed that people sometimes change their tastes (e.g., they like coffee with sugar but learn to like it without), it is sometimes tacitly assumed that almost any taste can be changed in any individual simply by "getting used" to a new taste. Several possibilities need to be... 

Beyond that, the sense of olfaction does not depend on the concentration of the odorant concentration invariance. If you are exposed to jasmine at very low concentration, it smells like jasmine if the concentration is significantly raised, it still smells like jasmine. Perhaps more to the point is the concentration invariance of complex aromas such as that of coffee. The brain forms a single perception from complex inputs, regardless of the intensity of the signal. Olfaction has this property in common with taste. 

The roasting of foods such as malt or coffee can result in bitter-tasting compounds however, until recently little was known about the chemistry of any compounds formed in the MaiUard reaction that could be responsible for such tastes. Frank et al. [33] identified a new class of compound, l-oxo-2,3-dihydro-lH-indolizinium-6-oxalates, from reaction mixtures containing xylose, rham-nose and alanine (Fig. 12.1). A number of such compounds have been reported and they appear to have low taste thresholds (below 1x10" mmol/L). 

---