What wineries want…..and why: Winegrape assessment in the vineyard and at the winery
Grape rape ma matt u r i ty 1. Tot otaal so solu lubl blee so solilid ds, pH an and d titr titrat atabl ablee acidity Current topics in this Winegrape Assessment Series include: Grower and winery expectations in grape production Grape maturity 1. Tot Total al soluble soluble solids solids,, pH and titratable acidity 2. Colour in red grape varietie varietiess 3. Croppi Cropping ng levels levels Grape purity 1. Diseas Diseases es - powdery mildew, mildew, downy mildew, mildew, Botryti Botrytiss and other moulds and rots. 2. Agroche Agrochemical mical residues 3. Matter other than than grapes (MOG) (MOG)
*Vitinotes in this series have been sources from Winegrape assessment in the vineyard and at the winery, the 2003 WGCA-WF WGCA-WFA A Liaison Committee report to the Grape and Wine Research and Development Corporation.
winemaker,, maturity is determined To the winemaker determined not only by 'sugar ripeness' but also by 'flavour ripeness' of the berries berries.. A range range of components components may be considered. consi dered. The sugar in in grapes is often used as
It is important for each parcel of grapes to reach a targeted maturity to maximise the quality potential at harves harvest. t. If the Baume Baume is below the the minimum minimum tolerance set by the winery for a given variety, variety, then
indicator of maturity and is sometimes used a basis for pricing of grapes. The majority of wineries measure sugar as total soluble solids (TSS) in degrees Brix and converted to Baume units. units. One unit of Baume is equivalent equivalent to 1.8 degrees Brix. Brix. Baume gives a convenient indication of potential alcohol content of the wine to be produced from the grapes, eg. grape grapess of 13 Baume, Baume, if fermente fermentedd completely completely,, produce a wine of about 13% alcohol by volume.
penalties may occur resulting in a loss of income to the grower. • TA and and pH are closel closelyy associat associated ed with Baume Baume and and can affect the resultant wine quality if out of balance. Acidity is important for flavour balance and a low pH leads to more stable colour and inhibits microbial spoilage spoilage.. Winemaker kerss take into conside cons ideration ration the TA and pH va value luess, and their their balance with the Baume level in deciding when to harvest. • Achi Achievi eving ng a Baume Baume below below the minim minimum um t o l e rance may resul resultt in poo poorer rer quali quality ty wine wines. s. Delivering grapes over and above the targeted
Titratable acidity (TA) and juice pH are commonly measured as well as TSS to give an overview of grapee maturity at harvest, grap harvest, and are used for harvest scheduling. TA and pH are not commonly used as an element for pricing grapes grapes.. As TSS increases in the berries, berrie s, the juice pH rises and the TA declines declines.. TA indicates the total amount of organic acids in solution and the pH relates to the free hydrogen ions in solution indicating the alkaline/acidity balance. As TSS, TSS, TA and and pH can be easily easily and objectively measured, measu red, they are commonly used as basic basic quality specifications related to maturity of grapes and therefore suitability for harvest. What are the implications of not meeting specifications? specifica tions? • Not meeting meeting the the minimum minimum tolera tolerance nce can can affect affect the resultant wine quality as Baume is closely linked with other quality characteristics such as colour, flavour and alcohol.
Baume, on the other hand, can result in high alcohol wines that may not be allowable for export and which are not to style. style. Costs can be high to remove excess alcohol from a wine. • If TA isis lower than requir required, ed, then acid acid adjustme adjustment nt is required resulting in increased costs in the winemaking process. BONUSES AND/OR PENALTIES ARE UNCOMMON FOR TA TA AND PH MEASURES ABOVE OR BELOW THE SPECIFICATION
What are some causes of not meeting specifications? • Seas Seasonal onal condit conditions ions greatly greatly affect affect the maturi maturity ty of grapes grapes.. Coo Cooler ler regions tend to experience a slower increase in Baume and TA often remains high. high. In some years when temperatures temperatures remain remain cooler than average, the cool regions may struggle to achieve the targeted Baume. Baume. Warm to hot regions tend to show a faster increase in Baume and TA levels in berries tend to drop as acids degrade at higher temperatures, often meaning TA must be artificially artificially adjusted in the winery. winery. It is commonly found that higher quality wines from a particular variety within a designated region are made from grapes that reach their targeted maturity maturity earlier earlier.. Grapes that do not have generally been harvestedd from vines that are out of balance harveste balance,, younger vines vines,, or vines that are are badly managed managed,, eg. over cropping, cropping, over irrigat irrigating, ing, inadeq inadequate uate pruning and/or poor canopy management. • High variabili variability ty within a block of of vines is of great great concern when
ASSESSMENT AT AT THE RECEIVAL RECEIVAL POINT Sampling devices used by winery representatives at the point of receival range from mechanical core samplers to smaller manual devices. devic es. Whatever tool tool is used, the aim is to obtain a sample sample that is representative of the the load. Tr Training aining is therefore essential essential to ensure consistency of operation: • For loads loads delivered delivered in grape grape bins itit is recommended recommended best practic practicee to sample every bin twice twice and average the result. result. A minimum would be to sample at least 50% of the bins once. once. If there is is significan significantt discrepancy discrep ancy between the bins, bins, then there is a need to sample further until variability is minimised. • For loads loads delivered delivered in tipping tipping trucks trucks and/or trailer trailerss it is recommended best practice to sample each load unit in three different sections and average the result. • Resul Results ts are recorded recorded and acted acted upon as per winery winery procedures procedures..
assessing maturity parameters as results can be affected if the variability is not taken into consideration when sampling the block. How specifications are evaluated TAKING MEASUREMENTS Using juice samples (for both pre-harvest assessment in the vineyard and load assessment assessment at the winery), TSS TSS,, TA and pH are all measured with standard calibrated instruments: • TSS is usuall usuallyy measured measured by refrac refractometry tometry,, givin givingg a value value expressed expressed in degrees Brix. The Brix value is then converted to Baume. • TA is is measured as free and bound hydrogen hydrogen ions by titra titration tion with with NaOH, express expressed ed in g/L. • pH is measured measured using using a calibra calibrated ted pH meter and values values are expressed in pH units. ASSESSMENT IN THE VINEYARD VINEYARD Sampling commences in the vineyard at around 8 Baume onwards for most varieties (ie. once berries have reached full veraison): • It is best best practice practice to to sample sample twice weekly weekly if resour resources ces allow, allow, or once weekly as a minimum. • Tak akee variability variability between between vines vines and bunches into into account by taking taking samples that are representative of the block or unit to be harvested. • Samples should be be taken taken at the same same time of day day each time time and preferably in the cool of the morning.
Delivering grapes to specification • It is Best Practic Practicee by the grower to deliver deliver grapes grapes to a targeted targeted Baume (set by the winemaker) for each variety as required for the designated wine style. • Many grape grape purchasing purchasing agreemen agreements ts apply apply a minimum minimum or maximum maximum tolerance - a measure for a specification above or below which penalties penal ties gener generally ally apply apply,, or gra grapes pes may be unaccept unacceptable able to the winery. Deliver grapes within the tolerance where a winery has written the specification specification to avoid penalties penalties,, especially where it may affect affect pricing or rejection is a risk. • The winery winery must must notify notify growers of results results which do not meet meet specifications (within specifications (within 2 hours is acceptab acceptable), le), to discuss the outcome. The appropriate winery staff should also be contacted immediately as load processing may be delayed.