This collaborative study was conducted to determine the total monomeric anthocyanin concentration by the pH differential method, which is a rapid and simple spectrophotometric method based on the anthocyanin structural transformation that occurs with a change in pH (colored at pH 1.0 and colorless at pH 4.5). Eleven collaborators representing commercial laboratories, academic institutions, and government laboratories participated. Seven Youden pair materials representing fruit juices, beverages, natural colorants, and wines were tested. The repeatability relative standard deviation (RSDr) varied from 1.06 to 4.16%. The reproducibility relative standard deviation (RSDR) ranged from 2.69 to 10.12%. The HorRat values were < or = 1.33 for all materials. The Study Director recommends that the method be adopted Official First Action.

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Determination of total monomeric anthocyanin pigment content of fruit juices, beverages, natural colorants, and wines by the pH differential method: collaborative study.

Copigmentation is a solution phenomenon in which pigments and other noncolored organic components form molecular associations or complexes. It generally results in an enhancement in the absorbance and in some cases, a shift in the wavelength of the maximum absorbance of the pigment. Copigmentation has not previously been taken into account in traditional wine color measures, in the relationship between color and pigment analysis, or in spectrophotometric assays for anthocyanin content. It is now apparent that copigmentation can account for between 30 and 50% of the color in young wines and that it is primarily influenced by the levels of several specific, noncolored phenolic components or cofactors. Copigmentation is of critical importance in understanding the relationship between grape composition and wine color, the variation in color and pigment concentration between wines, and in all reactions involving the anthocyanins during wine aging. This review focuses on the importance of the individual pigments and cofactors, the strength of their interactions, and their relative abundance in grapes and wines. A simple mathematical analysis of the solution equilibrium is developed to explain the nonlinear deviation from Beer’s law. When solved for typical wines, this function provides estimates of the apparent association constant, K, and the apparent molar extinction of the copigmented form, Ec, in natural mixtures. These measures allow the fraction of the anthocyanins which is in the copigmented form to be estimated. The significance of this phenomenon on pigment extraction and color retention during fermentations, on the rate of subsequent pigment polymerization, on the possible protection of anthocyanins from oxidation, and in the possible involvement on perceived mouthfeel and astringency of wines are suggested. Aspects of the copigmentation phenomenon that are poorly understood are identified and some research directions are suggested.

The copigmentation of anthocyanins and its role in the color of red wine: A critical review

From 1950 to 1999 the majority of the world's highest quality wine-producing regions experienced growing season warming trends. Vintage quality ratings during this same time period increased significantly while year-to-year variation declined. While improved winemaking knowledge and husbandry practices contributed to the better vintages it was shown that climate had, and will likely always have, a significant role in quality variations. This study revealed that the impacts of climate change are not likely to be uniform across all varieties and regions. Currently, many European regions appear to be at or near their optimum growing season temperatures, while the relationships are less defined in the New World viticulture regions. For future climates, model output for global wine producing regions predicts an average warming of 2 ∘C in the next 50 yr. For regions producing high-quality grapes at the margins of their climatic limits, these results suggest that future climate change will exceed a climatic threshold such that the ripening of balanced fruit required for existing varieties and wine styles will become progressively more difficult. In other regions, historical and predicted climate changes could push some regions into more optimal climatic regimes for the production of current varietals. In addition, the warmer conditions could lead to more poleward locations potentially becoming more conducive to grape growing and wine production.

Climate Change and Global Wine Quality

Secondary phenolic metabolites play an important role in plant defense mechanisms, and increasing evidence indicates that many are important in human health. To date, few studies have investigated the impact of various agricultural practices on levels of secondary plant metabolites. To address this issue, the total phenolic (TP) content of marionberries, strawberries, and corn grown by sustainable, organic, or conventional cultural practices were measured. Additionally, the effects of three common postharvest processing treatments (freezing, freeze-drying, and air-drying) on the TP content of these agricultural products were also investigated. Statistically higher levels of TPs were consistently found in organically and sustainably grown foods as compared to those produced by conventional agricultural practices. In all samples, freeze-drying preserved higher levels of TPs in comparison with air-drying.

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Comparison of the total phenolic and ascorbic acid content of freeze-dried and air-dried marionberry, strawberry, and corn grown using conventional, organic, and sustainable agricultural practices.

This review discusses the impacts of nitrogen addition in the vineyard and winery, and establishes the effects that nitrogen has on grape berry and wine composition and the sensory attributes of wine. Nitrogen is the most abundant soil-derived macronutrient in a grapevine, and plays a major role in many of the biological functions and processes of both grapevine and fermentative microorganisms. Manipulation of grapevine nitrogen nutrition has the potential to influence quality components in the grape and, ultimately, the wine. In addition, fermentation kinetics and formation of flavour-active metabolites are also affected by the nitrogen status of the must, which can be further manipulated by addition of nitrogen in the winery. The only consistent effect of nitrogen application in the vineyard on grape berry quality components is an increase in the concentration of the major nitrogenous compounds, such as total nitrogen, total amino acids, arginine, proline and ammonium, and consequently yeast-assimilable nitrogen (YAN). Both the form and amount of YAN have significant implications for wine quality. Low must YAN leads to low yeast populations and poor fermentation vigour, increased risk of sluggish/stuck/slow fermentations, increased production of undesirable thiols (e.g. hydrogen sulfide) and higher alcohols, and low production of esters and long chain volatile fatty acids. High must YAN leads to increased biomass and higher maximum heat output due to greater fermentation vigour, and increased formation of ethyl acetate, acetic acid and volatile acidity. Increased concentrations of haze-causing proteins, urea and ethyl carbamate and biogenic amines are also associated with high YAN musts. The risk of microbial instability, potential taint from Botrytis-infected fruit and possibly atypical ageing character is also increased. Intermediate must YAN favours the best balance between desirable and undesirable chemical and sensory wine attributes. ‘Macro tuning’, of berry nitrogen status can be achieved in the vineyard, given genetic constraints, but the final ‘micro tuning’ can be more readily achieved in the winery by the use of nitrogen supplements, such as diammonium phosphate (DAP) and the choice of fermentation conditions. This point highlights the need to monitor nitrogen not only in the vineyard but also in the must immediately before fermentation, so that appropriate additions can be made when required. Overall, optimisation of vineyard and fermentation nitrogen can contribute to quality factors in wine and hence affect its value. However, a better understanding of the effect of nitrogen on grape secondary metabolites and different types of nitrogen sources on yeast flavour metabolism and wine sensory properties is still required.

Implications of nitrogen nutrition for grapes, fermentation and wine

Principles of Sensory Evaluation of Food

Sampling. Soluble Solids. Acidity and Individual Acids. Alcohols. Carbonyl Compounds. Esters. Nitrogen Compounds. Phenolic Compounds. Chemical Additions. Other Constituents. Gases. Wine Color. General Chemical and Equipment Information and Theory. Index.

Methods for analysis of musts and wines

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 The utility of a given variety of grapes for wine making depends upon several factors.
 These include production factors such as scion-stock interrelationship, susceptibility
 to disease, inherent vigor of the vine, resistance to frost (which depends on the
 time of leafing out, the vine’s ability to produce crops after frost injury, and the
 like), and the yield and composition of the grapes under various soil and climatic
 conditions. One must also carefully evaluate: (1) the influence of environmental conditions
 (rainfall, wind, fogs, humidity, exposure, mean daily temperature, and time of maturity);
 (2) the adaptability of the must to various vinification and amelioration practices
 (temperature, type of yeast, aeration, and other variations); (3) the suitability
 of the wine for aging in the wood and in the bottle (rate of clarification, bouquet
 development, and resistance to disease); and (4) the basic quality of the wine produced
 by the variety. The production of wine may be considered as the complex interrelation,
 interaction, and mutual influence of all these factors with and upon each other. In
 order to study wine-grape-variety adaptation in California, one must consider each
 of these critically and separately.
 The primary problem in enology is to determine the influences which affect the utility
 of a wine. Since grapes are the raw material, a study of the various varieties is
 the starting point. Because of the numerous variations in environmental conditions
 in California, the experiments must be repeated with each variety in as many different
 localities as possible.

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Maynard A. Amerine

Papers

Principles of Sensory Evaluation of Food

Methods for analysis of musts and wines

Composition and Quality of Musts and Wines of California Grapes

The technology of wine making

Wines - Their Sensory Evaluation