Pressing Grapes

In the wine making process the crushing and de-stemming process releases the “free run” juice from the grape. While this is top notch quality juice there is still quite a bit of juice remaining in the grapes. This is where pressing comes in. After all, more juice means more wine! Red wines are nearly always made from both free run juice and pressed juice. White wines on the other hand are not always pressed. The very best white wines are made from only the free run juice. Historically pressing grapes was done by hand or by people stomping grapes. This is not a very sanitary way to go about making wine! Imagine drinking a Zinfandel with an athlete’s foot aftertaste. Today most wineries use a mechanical press of some sort. These come in two basic varieties, batch presses and continuous presses. Two Types of Presses A batch press can handle up to 1-5 metric tonnes per hour with an appropriate team of winemakers on the job. By in large this is the type of press used by amateur wine makers as well as small to medium sized wineries. Grapes are loaded in one “batch” at a time. Different presses can handle different quantities of grapes. Continuous presses on the other hand are generally motorized and fed a continuous stream of grapes. Because of this automation continuous presses can press up to 100 metric tons per hour. As you might have guessed a continuous press is geared more for a factory winery pressing thousands of tons of grapes at harvest. For now let’s concentrate on batch presses. Two Types of Batch Presses Basket Presses The earliest known mechanical press is the basket press. Still used today at the amateur and professional level this iconic piece of machinery is still a reliable way to go. A basket press has a ring of vertical staves with gaps between them where the pressed juice pours forth. Grapes are loaded in the top. Then a wooden plate is lowered down over the grapes and a ratchet is used to slowly apply pressure to the grapes. When using a basket press wine makers will often add rice hulls to the layers of grapes. These hulls are inert and do not impart any flavor into your wine. What they do is pierce the skins to a) release more tannins and color from the skins and b) provide a path for the pressed juice to flow. If you don’t use the rice hulls the juice will flow very slowly and you’ll leave a lot behind. Bladder Presses Also known as pneumatic presses these are quite common in small to medium sized wineries. These presses have either vertical staves as on the basket press or a cylindrical piece of sheet metal with holes in it for the pressed juice to flow through. The difference is the pressing mechanism. In the middle of the press is a rubber bladder than is filled with either water or air. As it expands from the center of the press the grape skins are pushed up against the outter ring. Because air is compressible this...

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