Harvest: deciding when grapes should reach the cellar
No single measurement determines a harvest date. Intended wine style, representative sampling, different signs of ripeness and processing capacity all help build a meaningful picture.
Harvest is more than the day on which grapes become sweet enough. It is useful to think of it as a series of decisions: what wine does the producer intend to make, what do the samples show, and when can the fruit be received properly? An early or late date alone tells us little about the eventual wine’s quality.
Ripe for which wine?
The Australian Wine Research Institute relates ripeness to the intended wine style. Retaining acidity for a fresh white wine can favour earlier picking. Sugar accumulation, acid decline and aroma development can progress at different rates.[1]
Examining the pulp mainly informs us about the juice’s sugar–acid balance. For skins, the condition and extractability of aromas and phenolic substances also matter, since these contribute components to the wine. Seed lignification is assessed separately, particularly for red wine. It can lag behind other signs of ripeness, so a sweet berry is not necessarily equally mature in all its parts.[1]
A sample should represent the vineyard
The VITICARE manual published through AWRI highlights variation between vines, bunches and even berries within a bunch. Sampling should represent fruit in different positions and exposures. A repeatable method, clear identification and suitable handling of samples also matter when interpreting the results.[2]
In practice, samples therefore include fruit from several vines and different parts of the bunch. The manual also addresses labelling samples, keeping them cool and analysing them promptly. Repeating the same sampling method helps reveal how fruit in the area is changing; one unusually sweet berry tells us only about itself.[2]
What do the measurements show?
A refractometer measures how expressed grape juice refracts light. A scale calibrated using sugar solutions then provides an estimate of sugar content; Brix and Baumé are examples of such scales. The reading characterises the must, rather than giving the finished wine’s alcohol content. Instrument calibration and sample temperature also influence the result, making a consistent measurement procedure important.[3]
Two different readings describe acidity. pH reflects acidity associated with free hydrogen ions; a lower value means a more acidic medium. Titratable acidity measures the amount of acidity that can be neutralised. Juices with the same titratable acidity can have different pH values because the acids’ composition and behaviour matter. pH also influences wine’s microbiological stability: the two measurements answer different questions.[4]
Waiting and processing both matter
AWRI’s research on harvest timing distinguishes sugar accumulation from a rise in sugar concentration caused by water loss. A higher reading therefore does not automatically mean more desirable ripeness. The research also identifies compressed harvest schedules and processing capacity as important production considerations.[5]
Red-wine fermentation requires space for juice and skins together: while one lot occupies a fermenter, the next cannot use the same vessel. AWRI therefore identifies red-fermenter capacity as a particular bottleneck. The order of harvest coordinates grape ripeness with the cellar’s ability to process the fruit.[5]
How to approach a harvest-season visit
Arrange the visit beforehand and ask at the start which tasks are under way. Do not handle equipment or obstruct people at work. If conversation time is limited, choose one wine lot and three questions: what was the goal, what informed the picking decision, and what happens to the grapes next?
Return to those notes when you eventually taste the finished wine. Which of the producer’s intentions can you recognise, and which questions remain open? Such a comparison can teach more than simply recording how many days earlier or later harvest began than in the previous year.
Sources and further reading
- 1. Defining berry ripenessAustralian Wine Research Institute
- 2. VITICARE On Farm Trials Manual 3.1: Measuring Fruit QualityVITICARE / Australian Wine Research Institute
- 3. Measurement of total soluble solids of grapes and mustAustralian Wine Research Institute
- 4. Acidity and pHAustralian Wine Research Institute
- 5. Managing the impact of vintage advancement and compressionAustralian Wine Research Institute
