Harvest Flashcards
How to chose the right date of harvest?
Traditionally, the rule-of-thumb was that grapes ripened 100 days after the beginning of flowering. Especially in European regions, readiness for harvest has been measured by potential alcohol levels.
However, more recently the context for making decisions about harvesting dates has changed due to:
- a generally warmer climate: making it easier to ripen grapes in cooler regions
- better viticulture: enabling the vine to ripen grapes fully
- a focus on aroma and tannin ripeness, which is sometimes considered as more important than optimum sugar ripeness.
One overriding factor is the threat of rain in the harvest period (see Untimely Rainfall in Hazards). If rain is forecast, grape growers may have to choose between harvesting under-ripe fruit or risk leaving grapes on the vine in the hope that the weather will improve. Rain in the last days before harvest can lead to diluting of the juice or, in the worst-case scenario, splitting of the skins due to rapid expansion, with consequent threat of grey rot and loss of some or all of the harvest.
How to measure ripeness?
‘Ripeness’ is a term that can have a number of different meanings, as covered in Defining Ripeness in Grape Development. Therefore, grape growers will often be measuring various components in the grapes in order to decide the optimum time of harvesting for the style of wine they are aiming for.
- Sugar levels – The amount of sugar in ripening grapes is easily measured by a handheld refractometer. Most dry still wines are harvested between 19° and 25° Brix (one of the scales used to measure the amount of sugar in the juice), which will convert into 11–15% abv.
- Acidity levels - Titration can be used to calculate acid levels. (Titration is a method of finding out the amount of a substance in a solution by gradually adding measured amounts of another substance that reacts in a known way. Similarly, the PH of the juice can be read by a pH meter.
- Aroma and tannin ripeness – Usually determined by taste (with experience).
There are various ways of measuring other compounds in the wine (which may support decisions regarding when to harvest).
Alternatively, high tech means (visible or near infrared spectroscopy) are appearing on the market. The benefit of the latter is that they give multiple readings for sugar, acidity and various other wine compounds or measures. However, even with such detailed data regarding the components of grapes, tasting the grapes remains one of the most important ways of deciding when to harvest.
Explain harvesting dates for specific wine styles?
- Grape growers in the Loire harvest Chenin Blanc over a period of 4–6 weeks, according to the style of wine to be made: early for sparkling wine, mid-harvest for dry and off-dry styles and late for botrytis or late harvest styles (see Drying Grapes on the Vine in Concentrating the Grape Must).
- Grape growers in California can choose whether to harvest Zinfandel in early to mid- August for White Zinfandel or whether to harvest in September for red wine. As Zinfandel tends to have unripe and ripe fruit on the same vine, care has to be taken with selection if a consistently high quality is required. Equally, in hot areas grape growers must decide whether or not to include shrivelled grapes.
- Harvest dates are extremely influential for a number of wines that have residual sugar. Some of these wines are made by harvesting late to concentrate the sugars in the grapes. The grapes for botrytised wines often need hand-harvesting over several passes through the vineyard to select the most botrytised grapes at that time. In the case of Eiswein or Icewine, grapes can only be picked when temperatures reach below certain levels (e.g. below -8°C / 18°F for Canadian Icewine). For more details, see Specific Options for producing Wines with Residual Sugar.
- There is a continuing debate over whether extended ‘hang time’ is detrimental to wine style. Some critics believe it leads to overly alcoholic and unbalanced wines lacking in natural acidity and having extra-ripe fruit character. Some grape growers say that critics reward these wines with high scores and that consumers like them.
Explain the advantages and disadvantages of machine-harvesting?
Machine-harvesting has become the default option for inexpensive to mid-priced wine and for larger-scale production. (There are exceptions, e.g. in South Africa where most grapes are still hand-harvested because of the availability of labour at a low cost.) This is particularly the case where vineyards have been designed from the start to facilitate it. Vineyards are now prepared and planted to maximise their size with even row spacing, a turning space at the end of rows and are on flat land or land with a small, regular gradient.
In the past, machine-harvesting used to be equated with only acceptable to good level quality wines. However, several steps can be taken to improve quality today – at a range of different costs. These include:
- selecting out undesirable fruit by hand before harvesting by machine
- using a bow-rod shaking machine (rather than the older machines, which beat vines to remove the fruit); this is gentler and can be set to be more selective
- investing in the very latest machines that have options for optical sorting devices on them and which can crush white grapes and add SO2 in the machine itself
- rigorous sorting on arrival in the winery, including removal of MOG (matter other than grapes) and unripe and rotten grapes.
Advantages of machine-harvesting:
- Harvesting by machine is significantly faster and substantially cheaper in large vineyards, if the vineyards have been designed with this in mind. The proportions vary depending on the cost of labour and of machines, but studies conducted in California indicate that machine-harvesting can be one-third of the price of hand-harvesting.
- Machine-harvesting avoids issues of the lack of availability of, and possible unreliability among, casual workers.
- Grapes can be harvested at night and be kept up to 15°C / 59°F cooler (than if they were picked during the day) and therefore in better condition. This can reduce microbial spoilage and oxidation.
- For white, fruity wines, starting the winemaking with cool fruit preserves the intensity of fruit aromas. It also helps to save the cost of refrigeration.
- The timing of the harvest can wait until the desired level of ripeness has been achieved and then carried out quickly. By comparison, assembling and deploying a group of pickers may be less flexible and slower.
Disadvantages of machine-harvesting:
- Machine-harvesting, despite all the advances, is still less gentle than hand-harvesting. It involves grapes being shaken off the stems (potentially leading to rupture of the grape skin and some release of juice), rather than keeping the bunches intact. This is a consideration when making some styles of wine where whole bunches are required (see Hand Harvesting Required) and when wishing to avoid any oxidation or the extraction of phenolic compounds (see Wine Components), for example with delicate white wines.
- It is not economic or practical for small-scale vineyards. Rental or ownership of a machine is not cost effective for small vineyards.
- Machine-harvesting may be unsuitable for grape growers that have several different varieties ripening at different times in the same plot (depending on the size of the plot and organisation of the different varieties within the plot).
- It is not suitable for vineyards on steep slopes or with limited access.
- The quality of the work is only as good as the skills of the operator.
- Where an estate does not own its own harvester, there may be competition for the rental of the machine at the best moment for harvest.
- Purchasing a harvester is a major investment.
Explain the advantages and disadvantages of hand-harvesting?
Advantages of hand-harvesting:
- Pickers can be highly selective at a bunch-by-bunch level and to remove any diseased, under- or extra-ripe fruit at the point of harvest.
- Pickers can deal with steeper slopes, irregular rows and mixed plantings in the same vineyard.
- If handled with care and put in small, stackable crates (with a maximum weight of 10–15 kilos), the crushing of grapes and the release of juice, which would then be prone to oxidization and to microbial spoilage, can be avoided.
Disadvantages of hand-harvesting:
- It is more expensive than machine-harvesting in medium to large vineyards
- It requires the availability of a reliable work force and their training and supervision to ensure that they work to the required standard
- Harvest has to be carried out in daylight hours and may not be able to avoid high temperatures; this raises the chance of grapes being spoiled by microbes or oxidation.
Rising labour costs, the scarcity of labour and the advantages of machine-harvesting are making some producers of premium wines reconsider their options. By comparison, some inexpensive, high volume wines may be harvested by hand or part harvested by hand. For example, cooperatives in France or Italy receive fruit from small-scale grape growers and then use the fruit for large batches of wine.
With what styles of wine hand harvesting is required?
Some wine styles require hand-harvesting. These include premium sparkling wines made where whole bunches are required for whole bunch pressing (Champagne and most bottle-fermented sparkling wine around the world).
Similarly, grapes for Beaujolais and other wines that will be made by carbonic or semi-carbonic maceration require whole bunches for the process. In addition, if making a style of wine that requires selective harvesting of certain grapes, harvesting must be done by hand. For example, pickers may be instructed to harvest only botrytis-affected bunches (e.g. for Trockenbeerenauslese Riesling in the Mosel).
Grapes are also hand-harvested where they are grown on steep slopes (e.g. in the Douro Valley) or uneven land. Bush vines are harvested by hand because, to be machine harvested, vines need to be held on a trellis. Without the trellis, there would be too much damage to plants and the grapes.
