Crush Pad Operations
Harvesting Wine Grapes
Mature fruit should be harvested in a manner that produces the least damage since broken berries and juice will encourage uncontrolled enzymatic activity and microbial proliferation. Typically, most wineries will go through the vineyard several weeks before harvest and remove any bunches that have unripe or damaged fruit (Goldammer, 2021). During the harvest, some grapes are unavoidably broken and their juice released, whereas others may be bruised. Thus, oxidative browning often begins before the grapes reach the winery. Red grapes are certainly less sensitive to maceration and oxidation phenomena than white grapes. The juice also becomes field-inoculated with the yeast and bacterial flora present on grape surfaces. This is especially a concern during the heat of the day when undesirable microbial contamination can rapidly develop. To minimize this occurrence, grapes may be sulfited after harvest or harvested during the cool parts of the day or night by taking advantage of lower ambient temperatures.
Order of Grape Harvest
Sparkling wine grapes are harvested first (Chardonnay and Pinot Noir) to ensure lower sugar levels (Brix). Most of the white wine grapes make their way to crush. Viticulturally speaking, the red wine grapes are typically next in the harvest line, as they take a bit longer to reach full maturation. Finally, the ice wines make their way to crush after undergoing some serious dehydration on the vine to produce a raisin-like grape with highly concentrated sugars—perfect for dessert wines.
Addition of Sulfur Dioxide
The skin of the grape berry has a waxy layer and can be host to damaging microorganism such as Lactobacillus, Pediococcus, Acetobacter, and others. Some of the resident microbes on grapes are beneficial; however, many are not and can cause numerous problems if they are not managed correctly.
Harvest Reception
The harvested grapes arrive at the winery in plastic lugs, half-ton macro bins, or gondolas are emptied into a vibrating receiving hopper, which in turn feeds a steady flow of grapes to the destemmer followed by sorting and then crushing if needed. In some cases, the winery may first sort the grapes before destemming.
Onsite Grape Sampling
Sampling grapes on delivery to the winery can help to facilitate later stages of processing. It can also be the basis of rejection of grape deliveries if the analysis is done in near real time. For this reason, sampling of the grapes and rapid analysis as the grapes arrive and are weighed is becoming more common. This information can then be used to plan for necessary additions and adjustments prior to the must reaching the press or tank.
Receiving Hoppers
When grapes arrive at the winery in bins, they are typically dumped into hoppers that feed the first unit operation, which could be a sorting table, crusher/destemmer, or press. Receiving hoppers are available in various designs (Figure 2.2). In general, a horizontal or inclined helical screw in the bottom of the hopper regulates throughput and it should turn slowly to avoid excessive crushing of the grapes. This type of equipment generally works well although some berry breakage is expected due to the shear force generated at the edge of the screw.
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