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Grape Machine Harvesting and Wine Quality
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If I were to ask you what was probably the most important factor that has helped make high quality Australian wine so competitively priced in the world market. What would you say? Winery technology perhaps? Highly trained and skilled winemakers, maybe? The answer in part, and it is probably a major part at that, is…. machine harvesting. That's it. It is not widely known that well over 90% of Australia's grape crop is harvested by a machine, and that for most wineries, having teams of pickers slaving in the mid-day sun is a distant memory.
Machine harvesting fruit substantially brings down the cost of getting the grapes from the vineyard to the winery. The exact saving depends on a number of factors, but 60-70% savings are a pretty average result. However, does this practice lower the quality of the grapes and the finished wine? The ill-informed purist would say yes (as most of the great French vineyards are harvested by hand), but the evidence suggests otherwise.
Let's look at the process. Machine harvesters essentially remove the fruit from the vine by either slapping it using paddles or by shaking the vine. The kinetic energy imparted to the grape bunch by the harvester causes the bunches or (more typically) individual grapes to fly off the grape bunches, to be caught by the machine as it passes down the row. Machine harvesting is rather 'rough' in that it causes a fair amount of juicing of the grapes and may also collect other material such as leaves, shoots, the odd lizard etc., collectively known as MOG (material other than grape).
Juicing causes the grape juice to come in contact with the skins resulting in juices that are higher in phenolics. This occurs because grape phenolics are located primarily in the skins of grapes. Therefore the rupturing of the grape berry results in the skin phenolics leaching into the juice as it sloshes around in the back of the picking bins prior to them reaching the winery. Phenolic pickup is not an issue with red grapes (they are fermented on their skins anyway), but with white wines, skin contact can result in a loss of delicacy as a result of the pick-up of a hard bitter (phenolic) characters in the finished wine. White wines high in phenolics also age much faster as oxidative browning relies on the presence of phenolic substances.
Different grape varieties are more prone to juicing than others due to the toughness of their skin, and turgor of their flesh. For example, Semillon is a variety that heavily juices when machine harvested. The grapes of some varieties are also simply more difficult to shake off the bunch than others. Grenache and Zinfandel are two varieties whos grapes need more 'persuasion' to separate themselves from their bunches. It's just a physiological thing.
However, machine harvesting has one major quality advantage over hand harvesting. Machine harvesting is nearly always done at night. As a result, the fruit will arrive at the winery 10-20OC cooler than hand harvested fruit, that was picked during the day. The rate of juice browning and oxidation in general are temperature dependent. The higher the temperature, the faster it happens. So although the machine harvested fruit will on average have a higher phenolic load than hand harvested fruit, the rate of oxidation is slowed due to the fruit being cooler. Incidentally, cooler fruit also improves the efficiency of wineries, as having to cool the fruit down using refrigeration prior to fermentation slows down the grape through-put, not to mention increasing the winery's power bill.
It is worth noting that machine harvested fruit is not suitable for the production of all styles of wine For example, some winemakers produce fine delicate Rieslings by gently squeezing whole bunches using certain types of presses. Their aim is to minimise the degree of phenolic pickup in the juice as much as possible. Obviously this rules out machine harvesting as the majority of machine harvested fruit comes in as individual and partly juiced grapes. Carbonic maceration wines are made from intact berries, or more typically, intact bunches that are placed in a carbon dioxide rich environment. These conditions result in a special yeast free fermentation inside the grape berry which results in wines that display a distinct fresh 'cherry like' fruitiness. However if damaged berries are used, then the carbonic maceration fermentation will not occur and the resultant wine will in all likelihood have a high level of vinegar like volatility.
However despite these few limitations, most Australian winemakers have little option to work with machine harvested fruit. The economics and a lack of available labour demand that they do. However most winemakers do insist that they receive high quality machine harvested fruit from their growers or their vineyard managers. This has resulted in cooler fruit, with less juicing and much less MOG (something for which the lizards are eternally grateful).