Fruit Maturity Assessment

©Copyright Ben Rotter 2004-2008
www.brsquared.org/wine

Introduction

The timing of fruit harvest has a massive impact on wine quality. A wine will express the same characteristics as those of the fruit at harvest and is therefore no greater in quality than the fruit it is made from. Ideally, physiological changes in the fruit such as increases in sugar concentration, the maturation of tannins and the development of aromas/flavours would occur such that ideal levels of each coincided with a single harvest date. However, different fruit components such as these change at different rates and remain largely independent of each other. Instead, it is common for the development of aromatic/flavour compounds, sugar and tannin to progress at rates which do not converge on ideal levels at the same time.

Therefore, a holistic approach using multiple criteria is used to measure optimal fruit maturity. The definition of optimal maturity will vary according to the fruit and the desired wine style. For example, common dry white wine styles require maximum aromatic development yet sufficient acidity. Once the aims have been decided however, these criteria can be measured by periodic analysis of the fruit as it develops on the plant. The fruit can then be harvested at the correct time to meet these multiple criteria. If these criteria are not met, the knowledge gained in the data analysis from such sampling during ripening can help to determine how the growing and training practises of the plant can be modified to meet the criteria. Records of fruit data can be made to provide a historical database of sensory and analytical maturity profiles. This data can then be used to develop a maturity profile relevant to each given fruit and wine style.

Sugar concentration, acidity, pH and aromatic/flavour profile are the traditional measures used to determine fruit ripeness. These do not present a holistic analysis of fruit ripeness. However, they are the easiest to measure for the winemaker without advanced analysis equipment. In recent years, increasing focus has rightly been placed on tannic ripeness. The tannic maturity of a fruit plays a major role in wine quality, affecting wine balance, volume or body, tannic intensity, astringency, bitterness, dryness and ageability. Phenolic ripeness, particularly of fruit skins (in cases where fruits possess a significant skin), often occurs long after sugar/acid/aromatic ripeness. This aspect of fruit maturity is therefore added to the list of measures used to determine fruit maturity.

This article presents general information concerning the evaluation of fruit maturity using a holistic approach. It does not simply focus on sugar/acid balance, but a whole variety of maturity indicators. It also presents information on specific sampling and analysis techniques used to determine fruit maturity. These indicators can not only be used for winemakers growing their own fruit, but can also be used to assess the maturity level of purchased fruit. The background to this article comes from a focus on soft fruits. However, most information presented here can be applied to fruits in general.


Maturity Evaluation

General model

As a general model, the development of components in fruits might be shown as in Figure 1. It can be seen from the figure that, for example, as a fruit matures its sugar content increases whilst its acidity decreases. Understanding how a fruit matures is essential to making informed decisions on when to harvest. It also helps winemakers understand how the harvest date impacts on eventual wine quality. Using the previous example again, the earlier a fruit is harvested, the less sugar and the higher acidity it will possess.

As previously mentioned, different fruit components change at different rates. This figure, therefore, obviously shows ideal trends with regards to complementary component changes (e.g. full tannic ripeness coincides with full sugar ripeness). Nevertheless, such idealised behaviour is shown here as it is deemed most useful in understanding maturity development as a whole. These trends represent the generalised behaviour of fruit maturation with relative accuracy.


Figure 1: General trends of various fruit features during maturation

It should be noted that this figure shows the general trends of particular features averaged over the entire stem-skin-flesh-seed composite of a fruit. The preparation of this figure has been based on scientific research as much as possible (particularly on wine grape berry development). However, such information is not complete and it should be kept in mind that some of the graphical information presented above is anecdotal. Additionally, the concentrations in the graph are not relative (just because "tannin" is shown to have a higher concentration than "acidity" does not mean it is so). All features have been placed on the same graph using a non-relative scale for ease of presentation. Note also that véraison is defined as the point during fruit maturation at which coloured fruit varieties begin to lose their green colour and attain the colour they will possess at final ripeness. "White" coloured fruit varieties will attain a translucent skin.

The "tannic ripeness" in Figure 1 is a measure of tannic polymerisation (not of tannin quantity) and is again an average over the entire stem-skin-flesh-seed composite. Figure 2 shows the trends in the quantity of tannins in the seeds and skins, and the colour trend in the skins.


Figure 2: Trends in tannins and colour during maturation

Fruit maturity assessment

The aim of the winemaker is to obtain fruit harvested at a time at which all the features of the fruit are suitable for the wine type and style that is to be made. For example, for a dry white wine the fruit should have attained full aromatic development, yet with substantial acidity remaining within the fruit. Whilst for premium red wine quality standards, the fruit should have achieved a high level of tannic maturity without the acidity being too low.

Fruit maturity assessments, which follow the fruit's maturity development as it grows, can be used to determine when to harvest. Such assessments can be based on a variety of fruit attributes. These will be dealt with below.

Singular model approaches

Sugar/acid balance models have commonly been used to determine fruit ripeness. An example of such a model is that expounded by Cox [Cox, 1999] to assess grape ripeness. This model is used to determine grape ripeness and is based on sugar/acid balance. It states that if the product of the Brix and pH2 is in the range of 220 for whites or 260 for reds then the fruit is ripe. Such models can be very useful when used in parallel with other fruit maturity assessment techniques. (It should be noted, however, that the Cox index value range may not be suitable for red grapes grown in a warm climate, which often obtain Brix×pH2 values over 350 [Eisenman, 2003]). A similar model for determining grape ripeness uses the Brix value divided by the TA value (measured as tartaric and in units g/100ml) of the grapes. Cox advocates a value of 30-35 for ripeness using this index, whereas Gallander recommends values between 30 and 32 [Gallander, 1983]. Analysis of berry metabolites, proteins, or malate and tartrate content are examples of other techniques that have been used. However, the average home winemaker does not have access to the equipment required for such analyses.

Need for a holistic model/assessment

Such singular model approaches as the sugar/acid balance models are useful, but they neglect many features of maturity and as such do not present a complete model of maturity. For example, red grapes grown in certain climates may obtain "suitable" Brix×pH2 values before reaching full phenolic maturity. It is worth keeping in mind that there is no direct biochemical relationship between the accretion of sugar and the reduction in acidity. Nor is the plant's physiological mechanism for sugar production necessarily the same as that used to produce secondary metabolites such as aroma/flavour and phenolic compounds (definitely not in grape vines). Therefore, it is not always the case that sugar/acidity balance or malate/tartrate balance (or other single component models) coincide with the development of fruit flavours or phenolic ripeness. Such maturity analyses should therefore be used in parallel with other evaluation techniques. A holistic view should be adopted in assessing fruit maturity, where measures of sugar, pH, acidity, flavour/aroma profile, and phenolic quality and quantity are all included in the assessment.


Features of Maturity Assessment

A holistic approach to assessing fruit maturity involves tasting the fruit and conducting some analytical tests (e.g. measuring acidity and sugar concentration). Individual features of the fruit (e.g. the aromas/flavours within the flesh, the astringency of the skins, etc) can be observed and an evaluation of the degree of maturity can then be made. Knowledge of the fruit variety and the desired wine style is required to make meaningful evaluations of fruit maturity level (e.g. knowing how sweet a fruit needs to be to be deemed "ripe"). Even so, most fruit follow similar trends during ripening which can help guide the winemaker in deciding what is deemed "ripe" and what is not (see Figure 1 for example trends).

To follow fruit maturity progressively, comparative assessments can be made by freezing the fruit or fruit juice at various points in the ripening time frame. The defrosted fruit/juices can then be compared along side each other.

An assessment of fruit maturity would ideally include observing all the following features of a fruit:

Fruit Condition
  • aptitude to destem

  • fruit deformability/softness

  • adherence of flesh to skin and seeds

    •
    Flesh
  • sweetness

  • acidity

  • aroma/flavour profile

  • aromatic intensity

    •
    Skin
  • colour

  • texture

  • tannic intensity

  • acidity

  • astringency

  • tannic dryness

  • aroma/flavour profile

  • aromatic intensity


    • Seeds
  • colour

  • texture

  • aroma/flavour profile

  • tannic intensity

  • astringency


    • Stems
  • colour

  • aroma/flavour profile


    • Ability to ripen further


    Understanding fruit development: What to look for in obtaining riper fruit

    The following is a list of features used to determine fruit maturity. General trends during ripening are presented for each feature. Such knowledge can help the fruit harvester or winemaker follow fruit maturity development closely and ultimately make an educated decision as to when to harvest.

    It is important to keep in mind that some features are fruit and variety specific. Some fruit varieties may never reach the end point within the spectrums of ripeness detailed in the next section of this article. It is necessary for the winemaker to know the limits of such maturity development.

    Flesh

    The following features should be observed within the fruit's flesh:

    Flesh Texture

    The texture of fruit flesh generally develops in the following way as fruit matures:

    underripe -> ripe -> overripe
    firm -> soft -> mealy

    Aroma/flavour

    Varietal fruit character develops as fruit maturity increases. This can be assessed by smelling and tasting the fruit juice.

    Most fruits follow this general pattern of ripening in terms of aroma/flavour:

    Vegetative/Herbaceous -> Unripe Fruit -> Red Fruits -> Black Fruits -> Stewed Fruit/Jam

    An example of specific flavour components using this model for dark skinned grapes is as follows:

    Plant matter -> straw/vegetable -> apple/citrus/pear -> red fruits (cherry, strawberry, raspberry) -> black fruits (blackberry, plum, black cherry) -> jam/dried fruit (raisin, prune, date, jam)

    Other fruits such as gooseberries show a similar pattern: flavours begin at the plant/vegetal/herbaceous end of the spectrum and move through green fruits such as apple to tropical fruits.

    A wine cannot achieve a specific aroma/flavour without it being in the fruit used to make it. Aromatic/flavour development is therefore an essential factor of fruit selection for winemaking. Juice/fruit aromas should form an important part of a maturity assessment.

    The intensity of the aromas/flavour might also be noted. These tend to increase as the fruit matures.

    Tannin

    As a fruit matures, the phenolic compounds contained within it polymerise with other molecules such as sugars and proteins resulting in an organoleptic change. Tannin content is typically highest in the fruit seeds and skins and lower in the flesh.

    The general change follows the behaviour:
    Hard, bitter tannins -> astringent -> soft, supple

    An extract prepared from the fruit can provide a good base for making sensory analytical assessments with regards to tannins. See the Useful Assays section below for more details.

    A fruit extract such as that made in the Generic Tannin Assay (see below) would show the following feature trends:

    Extract colour: Low intensity --> Green, some colour --> Uniform yellow-straw or darker red/purple colour --> Uniform ambre/black colour, high extract
    Extract character: Acidic and astringent --> Less acidic and astringent --> Low acid and astringency --> Round, fine grained tannins

    Sweetness

    Sugar levels usually increase relatively dramatically during fruit maturation and then slow towards the end of ripening. Since sugar accounts for the majority of the soluble solids in relatively clear fruit juices, measuring the density of the clarified fruit juice is sufficient to give an accurate reading. Specific Gravity, Brix, and Baumé are all common density measurements made on fruit juice used for winemaking. A refractometer may also be used on fruit juices to determine their density. However, its measurement is only valid at levels higher than 15 degrees Brix in grapes since, under this value, other substances (organic acids, amino acids, precursors of parietal polyosides) in the grape have similar refractive indexes to sugar and cause inaccurate readings. The same is surely true for other fruits, but the Brix value will doubtless differ to that of grapes due to the presence or lack of the various acids etc.

    Acidity

    The acidity of fruit generally decreases as the fruit ripens. This is usually measured as titratable acidity from a sample of the juice.

    pH

    As fruit ripen, the pH generally increases. This can be measured from a sample of the juice. However, pH is highly dependent on the fruit's accumulation of minerals. In grapes, for example, the pH can be seen in simple models as a function of tartaric acid concentration and potassium concentration. Therefore, pH is highly dependent on growing conditions and can vary quite significantly from vintage to vintage.

    In some cases, fruit skins play a major role in the pH values of the flesh-skin-seed composite and pH evaluations should be made using these parts of the fruit, especially in cases where the fruit skins will macerate in must or wine.

    Stems

    Stems may be used to assist in determining fruit ripeness. In cases where fruit stems or seeds might be included in the fermentation, it is important to consider the ripeness of the stems themselves.

    As they mature, stems develop in the following way:

    Maturity level: Unripe --> Ripe --> Very ripe
    Colour/physical: Green --> Brown --> Brittle brown
    Aroma/Flavour: Leafy, vegetal --> Resinous wood, spice (cloves, cinnamon, pepper) --> Dried leaf, tea, herbal

    Stems usually contain a high proportion of phenolic compounds (tannins) of the fruit-seed-stem composite. These are mostly polymerised tannins and therefore appear astringent in the mouth.

    Skin

    As a fruit ripens, its skin changes colour. Of course this depends on the fruit and the variety, but in general colour development follows a pattern from lighter to darker colours.

    The physical texture of skins also change as they ripen. The tannins increase in intensity but become less acidic and less astringent.

    Overall, skins develop in the following way as they mature:

    Colour: Lighter --> Darker (highly dependant on variety)
    Physical texture: Hard --> Softer textured --> Chewy
    Aroma/Flavour: Herbaceous --> Neutral/slight fruitiness, slightly herbaceous --> Intense fruit, no herbaceousness
    Tannic intensity: Higher (rapid increase followed by decrease after véraison) --> Lower
    Acidity: Higher --> Lower
    Astringency: Lower --> Higher

    In general it is the quality and not the quantity of tannins which plays the more important role in wine quality. Taste descriptors are often adopted in subjective assessments of skin tannins. They are the same as used in wine tasting. Some descriptors include the following: hard, course, green, firm, chewy, dusty, supple, soft, fine and silky.

    Seeds

    Ideally, an assessment of seed maturity would incorporate observations of taste, colour, texture and brittleness.

    Seeds develop in the following way as they mature:

    Colour: Green --> Green-yellow --> Maroon --> Chestnut, no green --> Dark/tan brown
    Texture: Pliable, brittle, "wet" --> Woody, less brittle, "dry"
    Seed integrity: Seed strongly in tact with flesh --> Seed has lost most adherence to flesh
    Taste: Dry, astringent, bitter, harsh --> Less dry, astringent, bitter, harsh
    Aromas/Flavour: Grassy/herbaceous --> Toasted --> Almost roasted
    Tannic intensity: Rapid increase followed by slow but small decrease over the entire maturing period

    Seeds generally contain the highest proportion of tannins in the entire stem-flesh-seed composite. Seed tannic ripeness is therefore of high importance for musts/wines which macerate on the fruit seeds.


    Figure 3. Green-yellow seeds indicating under-ripe grapes

    Fruit condition

    As a fruit ripens the flesh (or pulp) becomes softer and loosens its bonds with the seeds and skin. Fruit deformability can be assessed by pressing the thumb into the fruit and visually assessing the deformation the fruit has undergone (see Figure 4). Skin may also be peeled from the fruit in a crude assessment of skin-flesh adherence.

    The aptitude for the fruit to destem is also an indication of maturity. A fruit will more easily detach from the plant/stem the riper it is.

    Fruit size and weight can also be used as a measure of maturity in the early stages of fruit ripening. Véraison is defined as the point in maturation when the fruit flesh physically softens and colour begins to develop.

    A summary of these features is as follows:

    Fruit flesh: Hard, firm adherence to seeds and skin --> Softer, less adherence to seeds and skin
    Fruit deformability: Low --> High
    Aptitude to destem: Low --> High


    Figure 4. Fruit deformability: easily demonstrated on a nectarine

    Ability to ripen further

    Finally, the ability for the fruit to favourably mature any further should be evaluated. It should be kept in mind at this point that not all features of a fruit develop at the same rate or in the same way. Judgements should therefore be made as to whether it is worth waiting longer before harvesting or not. See the "Complete Simple Maturity Assay Protocol" section for more on this.


    Fruit Sampling Protocol

    Fruit sampling for maturity assessment requires the attainment of a representative sample of fruit. Different fruits, even on the same plant, show considerable variation in their sugar, acidity, etc concentrations. Thus, if maturity assessment data is to provide a meaningful measure of maturity, fruit selection must be carried out with care. Clusters of fruits (e.g. a grape cluster) can be extremely heterogeneous. Likewise, the degree of ripeness from one fruit to another can vary significantly on the same plant.

    Note that if the results of the assessment/assay are to represent fruit quality characteristics after crush, the same crushing procedure should be used in the assay as will be used when preparing the must.

    The following guidelines will help to obtain a sample of fruit representative of the entire crop to be harvested:

  • Many different plants (vines/bushes/trees) should be used

  • Take a minimum number of berries/fruits from a large number of plants (vines/bushes/trees)

  • It is common to unconsciously pick more mature berries, therefore it's best to randomly select a berry/fruit with the minimum scanning of the fruiting zone possible.

  • Sample according to fruit distribution on the plant (e.g. if one side of the plant bears the majority of fruit, sample more fruit from that side to proportionally match the distribution)

  • Sampling should be taken at roughly the same time of the day

  • Sampling should consider topography, soil type and depth, plant age and vigour (select fruit from areas varying in all these characteristics)

  • Avoid selecting fruit from plants at the peripherals of the growing region (e.g. at side rows of a vineyard/orchard/etc)

  • For cluster-fruiting fruits, entire clusters should be removed to minimise fruit damage

  • For cluster-fruiting fruits, select berries from various regions on the cluster (i.e. at top, middle and lower vertical positions, and on various sides)

  • If the fruit is to be transported, it should be kept cool (10-15 C, 50-60 F) to preserve it

    •
    For grapes,
  • 10% of vines should be sampled

  • Around 2 kg (4 lbs) of fruit should be picked for a single analysis (this is ~10-15 clusters). At least 500 berries should be analysed, but 1000-2000 is preferable.

  • For red varietals, sampling should begin 15-20 days after mid-véraison

  • For red varietals, 200 berries should be used for phenolic analysis

  • For an accuracy of +/- 1.0 degree Brix (with a 95% accuracy) in subsequent juice density analysis, two lots of 100 berries should be sampled [Amerine and Roessler, 1958a & 1958b]

  • For an accuracy of +/- 0.5 degrees Brix in subsequent juice density analysis, five lots of 100 berries should be sampled [Amerine and Roessler, 1958a & 1958b]

    •

    Complete Simple Maturity Assay Protocol

    The following maturity assay protocol assesses each of the aspects of maturity discussed above in a logical sequence, from picking the fruit off the plant through to crushing it. Figure 5 below presents the various assessments that can be made with respect to each part of the fruit. For each feature, the observations found in the fruit can be compared with those detailed in the above section and an evaluation of the level of maturity can be made.


    Figure 5: Maturity assessment protocol sequence

    It should be noted that the sample preparation method (fruit collection and transportation, crushing, pressing, and cold settling) affect the titratable acidity and pH in particular. For the characteristics observed in maturity assays to be representative of the musts' characteristics, the same methods as will be used to crush fruit during must preparation should be used in the assay.

    Fruit condition

    As the fruit is picked from the plant, its aptitude to destem can be assessed. The fruit deformability/softness can then be assessed by pressing a thumb into the fruit and visually assessing the deformation the fruit undergoes.

    Separation of skins, seeds and flesh

    The physical components of the fruit can then be separated. For small berry fruits, where the assessment of skins is of high importance, the skins can be removed by squeezing the flesh/pulp and seeds out between the thumb and forefinger. Alternatively, fruits can be dissected around their circumference using a blade and the flesh can be scraped out. It may be worth noting the adherence of the flesh to the skin and seeds at this juncture in the procedure.

    Stems

    Stems can be separated and their colour assessed. To assess their aroma/flavour profile the Generic Tannin Assay can be used. However, many winemakers may feel that for stems this is not worth the bother and a visual assessment is sufficient.

    Flesh

    The flesh should be crushed in a similar manner as it will be for later must preparation. The sugar concentration, titratable acidity and pH can then be measured, and the aroma/flavour profile, aromatic intensity and tannic profile assessed.

    It is important, however, to keep in mind that the TA and pH analyses in particular will be affected by the presence or absence of any leachate from the skins in the analysis. Additionally, for fruits where considerable aroma/flavour is stored in the skins, the evaluator should remember that the flesh represents only part of the total aromatic profile. Such data is useful in maturity evaluation, but its solitary use with respect to must composition is questionable. Should the winemaker desire an analysis specifically relevant to must composition, the fruit should be wholly crushed and macerated in a manner representative of that which the fruit will undergo when preparing the must.

    Figure 6. Dissection of a gooseberry showing skin (left) and flesh (right) Figure 7. Dissection of a gooseberry showing seeds (left) and half of the whole fruit (right)

    Skins

    Not only is an assessment of skin characteristics helpful in an analysis of fruit maturity, but such characteristics are important to wine quality if the must/wine is macerated on the fruit skins. For example, grapes contain considerable quantities of aromatic compounds within their skins which impact significantly on wines where skin maceration has been practised.

    Some fruits such as red grapes contain considerable quantities of aromatic compounds within their skins. Assessment of grape skin quality is therefore essential to determining fruit and final wine quality. For aromatic assessment of fruit skins, the following assay can be used:

    Fruit skins, already separated from pulp/flesh and seeds, should be weighed. (In the case of grapes, a suitable quantity to use is 150-200 berries. The skins of these should weigh approximately 60-120 g.) To these 75 ml of 9.25 g/l citric acid solution is added to an approximate pH of 3.50 as well as pectin destroying enzyme. The mixture is blended with quick pulses until mixed thoroughly. 8% pure alcohol is added to the blended solution, and enough water added to take the final weight of the mixture back to that of the original weight of the fruit (the 150 berries in the case of grapes). The mixture is placed is a sealed bottle overnight at room temperature. This solution is then filtered to remove solids with the minimum handling possible and the solution tasted for aromatic intensity and tannin quantity and quality.

    A subjective assessment of the solution's colour can be made. The observations of colour, aromatic/flavour and tannin can be compared with the typical trends of fruit maturity development detailed in the "Understanding fruit development: What to look for in obtaining riper fruit" section above.

    As example of such a subjective assessment might be:
    Fruit assessed: red grape
    Solution extract colour: shows maroon colour
    Solution extract flavour: shows red fruits (cherry, strawberry, raspberry) characters
    Solution extract tannins: shows astringent tannins of moderate intensity
    Fruit is therefore deemed: moderately ripe (and is yet to show darker colour, black fruit flavours, and soft/supple tannins).

    Aromas of pomace (or leafy/tealike aromas) are from the tannins. A lack of varietal aroma or intensity in this extract means a wine made from such fruit will also lack varietal aroma or intensity.

    Seeds

    Seeds should at least be observed for colour, but might also be tasted for an appraisal of their tannic intensity, astringency, texture and aroma/flavour profile. Seeds can be assessed by tasting and their attributes evaluated according to the above section regarding their development. Additionally, the Generic Tannin Assay can be used on seeds (see below).

    Ability to ripen further

    After the above assessments have been made, an appraisal of whether the fruit can desirably ripen any further should be made. Here, an analysis of all the maturity indicators should be considered. Such indicators should then be compared against each other with regard to the expected future trends that will occur.

    For example:
    Can full tannic ripeness be achieved without an unsatisfactorily high increase in sugar concentration - the wine may contain ripe tannins, but would 14% alcohol by volume suit the style?
    Can the fruit be left to ripen further before imminent rains arrive, the result of which may destroy fruit and reduce quality?
    Can a fully developed aromatic/flavour profile develop before a significant (unsatisfactory) drop in acidity?

    Obviously, such questions depend on the climatic conditions and restrictions on the winemaker (for example, acid may be added to the must with regards to the last question). In any case, it is important to ask the appropriate questions when making this last assessment.


    Useful Assays

    The following fruit component-specific assays can be used for particular assessments.

    Skin aromatics assay

    For an assessment the aromatic profile and intensity of the skins, the following assay can be used:

    Take a statistically significant sample of fruits and carefully separate the skins from the flesh. The maceration of the skins should then be matched to that which they will undergo during later must/wine maceration. (This may range from simple hand crushing through to a simulation of punching down by pulse blending the skins until thoroughly mixed.) Then add to the skins 200 ml of 15% ethanol (adjusted to pH 3.0 with tartaric acid) and pectin destroying enzyme. Place the mixture in an airtight vessel for a week, after which time the solution is strained to remove solids. The liquor extracted will give an estimate of aromatic profile and intensity.

    For comparative assessments, the same amount of skins should of course be used for each separate assay.

    Generic tannin assay

    For an assessment of the tannic profile of stems or seeds or skins, the following assay can be used:

    Take a statistically significant sample of fruits and weigh it. Carefully separate the components to be used in the assay from the rest of the fruit. Add to these enough alcohol to make a 12% alcohol solution and adjust the pH to 3.2 with tartaric acid. (Note that pH 3.2 will result in easily extractable compounds whereas the same assay conducted at pH 1 will give an indication of total potential phenolics extractable.) Then add enough water to take the final weight of the mixture equal to that of the original weight of fruit. The mixture is placed is a sealed bottle overnight at room temperature. This solution is then filtered to remove solids with the minimum handling possible and the solution tasted for aromatic intensity and tannin quantity and quality.

    For comparative assessments, the same amount of stems/seeds/skins should of course be used for each separate assay.

    Example:
    1. 200 g fruit obtained
    2. Flesh removed by knife/scalpel and seeds removed
    3. 24 ml pure alcohol (200 g fruit × 0.12 alcohol) added to seeds
    4. 176 ml water added (200 - 24 ml)
    5. Tartaric acid added to pH 3.0
    6. Mixture sealed and left overnight at 20°C (68°F)
    7. Mixture strained through sieve and tasted

    Total fruit preservation assay

    To preserve the entire flesh-skin-seed composite for later assessment, the following assay can be used.

    Press the fruit at around 2°C (36°F). Add pectin destroying enzyme as well as 50 mg/l ascorbic acid and 30 mg/l sulphur dioxide. Transfer the solution to CO2 sparged storage vessels and store at 0°C (32°F). Solutions prepared in this way should remain in good condition for aroma/flavour assessment for several months according to Zoecklein [1995].


    Call for Ripeness Data

    If you have data (sugar concentration, acidity, pH, aromatic/flavour profile, or tannin profile) on a particular fruit that you feel represents the fruit's state at ripeness, the author would be interested in hearing from you (please email benrotter@spam.co.uk where "spam" is replaced with "yahoo"). A collection of similar data is available on this website on the Advanced & Reliable Fruit Data page.


    Further Information

    If you are interested in more advanced grape-specific maturity assays try:

    Douglas Adams Assay
    Vinovation (modified Gironde) approach; Boulton-Modified Somers Colour Analysis; Adams-modified Hagerman and Butler Polymeric Pigment and Tannin Spectrophotometer Assay
    Details of various chemical assays
    Advanced tannin measurement: Lowenthal Permanganate Titration and Folin-Ciocalteau Colorimetric Reaction methods


    Bibliography

    Amerine, M.A. and Roessler, E.B. (1958a). Methods for determining field maturity of grapes. Am. J. Enol. and Vitic. 9:37-40.
    Amerine, M.A. and Roessler, E.B. (1958b). Field testing of grape maturity. Hilgardia 28:93-114.
    Cox, Jeff. (1999). From Vines to Wines. Storey Books.
    Delteil, D. (2000). Evaluating maturity via grape tasting. Institut Coopératif du Vin News stand, April.
    Eisenman, Lum. (2003). Re: Measuring Brix. rec.crafts.winemaking UseNet Newsgroup post, 11/9/03.
    Gallander, J.F. (1983). Effect of grape maturity on the composition and quality of Ohio Vidal blanc wines. Am. J. Enol. Vitic. 34: 139-141.
    Jackisch, Philip. (1985). Modern Winemaking. Cornell University Press.
    Jackson, R.S. (1994). Wine science: principles and applications. San Diego Academic Press.
    Ribéreau-Gayon, P., Dubourdieu, D., Donèche, B., Lonvaud, A. (2000). Handbook of Enology, Volume 1, The Microbiology of Wine and Vinifications. John Wiley & Sons Ltd. (English edition).
    Zoecklein, B.W. (2001). Vintner's Corner and Enology Notes. http://www.fst.vt.edu/extension/enology/Jan-Feb01.html, January-February.
    Zoecklein, B.W. (1996). Vintner's Corner and Enology Notes. http://www.fst.vt.edu/extension/enology/july-aug96.html, July-August.
    Zoecklein, B.W., K.C. Fugelsang, B.H. Gump, and F.S. Nury. (1995). Wine Analysis and Production. Chapman and Hall, New York.


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