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Must pumps play an important role in the early stages of winemaking. Before the solid and liquids are separated, must pumps transfer the must from the destemmer to the crusher and from the crusher into fermenting tanks. During the red wine fermentation process, winemakers use must pumps to perform pump overs, which circulate liquid from the bottom of the tank back up to the top, where flavor, color, and other characteristics of wine are extracted from the suspended solids. While smaller-scale wineries traditionally perform manual pump overs, must pumps can save significant time and energy. Must pumps are major investments and making the right choice is critical. This guide provides a brief introduction to must pumps and how to decide what type of pump best suits your needs.
What's the flow-rate? The first question that any must pump buyer must address is the volume of wine that must be transferred. The flow-rate is measured in gallons per minute (GPM). Major vineyards often use wine pumps that transfer over 300 GPM, while a home winemaker might use a pump that transfers as low as 5 GPM. Some pumps have built in settings that allow the user to adjust the flow rate, while other pumps are fixed at one rate.
What functions will the pump be performing? Some large-scale wineries use specific pumps at different stages of the winemaking process. Certain pumps are better suited for specific pumping tasks, while some pumps are more versatile and can be used for pumping at any stage of the process.
How much does the pumping process aerate the wine? The amount of oxygen that wine is exposed to during the winemaking process can greatly affect the final product. During fermentation, oxygen exposure must be precise to avoid either underexposing or overexposing the must/juice combination. To learn more check out this Q&A.
How gentle is the pump in transferring must? Some pumps are more likely to damage important ingredients in must, which release unwanted compounds into the wine. This can lead to bitter or other odd tastes in the wine. Higher quality must pumps gently transfer the mixture as to prevent the release of such compounds. Wine is shear sensitive, which means that rough handling at any stage of winemaking can damage its delicate properties. To learn more check out this Q&A.
Is the pump self-priming? Certain types of wine pumps can begin operation with a simple flip of a switch. Others, however, need liquid in the pump to start running. To learn more check out this Q&A.
Is the flow pulsating? Do I need a pulse dampener? Most reciprocating PD pumps operate in ways that pump in pulses. While these pumps maintain a constant flow rate, some winemakers opt to use pulse dampeners to lessen pulsation.
What fitting size does a must pump need? Most must pumps have fitting sizes 3 inches or greater due to the solids that are being displaced. Larger fitting sizes can maintain high flow rates even at low speeds, as must can be pumped in large volumes slowly through bigger tubes.
Must pumps generally fall under the category of positive displacement pumps ("PD pumps"). PD pumps maintain relatively constant flow rates regardless of the viscosity of the material and the pressure from both the input end and the discharge end. Must is very delicate- rough pumping systems can damage the must and release unwanted compounds into the wine that can dramatically affect the final product's quality. PD pumps tend to pump must very gently, creating minimal turbulence. There are a number of different types of pumps that fall within the category of PD pumps:
Flexible Impeller Pumps are a popular type of pump for those looking to buy an all-in-one pump. Flexible impeller pumps operate using a series of flexible vanes extending from a single axis that create small cavities that are filled on the input end, then compressed before releasing the material on the discharge end. This creates a powerful suction, a very important feature when buying a pump for pump overs and uphill pumping. Compared to other PD pumps, flexible impeller pumps tend to be inexpensive. They are generally self-priming and easy to clean. To learn more check out this Q&A.
Rotary Lobe Pumps feature two large metal rotors that move in unison to create a constant flow rate. Rotary lobe pumps draw must into an expanding cavity before decreasing the cavity and pumping the must into an expanding cavity on the discharge end. Rotary lobe pumps are favored for their strong suction, which makes them an ideal candidate for pump overs and uphill pumping.
Screw Pumps displace a constant amount of must and liquid, rotating on a single axis with a screw inside a closed cavity that moves must through the chamber. Screw pumps, also known as progressive cavity pumps, handle solids very gently, but can be very expensive.
Peristaltic Pumps are generally favored by larger wineries, as they offer very high flow rates combined with very gentle handling. The outer edge of a peristaltic pump is lined with tubing that is compressed by rotating arms that create a vacuum, which draws material into the pump and subsequently releases it in pulses. Large peristaltic pumps can pump up to 20,000 gallons/hour. Peristaltic pumps are very easy to clean, as the must and wine being pumped is only ever exposed to the inner tubing. The must being pumped by the peristaltic pump never actually touches the mechanical parts, limiting damage and oxidization. Peristaltic pumps are very efficient, but do require regular maintenance of the tubing.
Air Diaphragm Pumps are extremely versatile and can perform most pumping tasks. Improved designs have greatly increased the popularity of air diaphragm pumps, which operate using compressed air as opposed to electricity. This does require that wineries using air diaphragm pumps have air compressors. While not regarded as the most gentle must pump, their low price and versatility have made them a staple of small wineries. Some winemakers prefer air diaphragm pumps for must because they do not create any friction with the grape pulp, seeds, and skin.
Speed control can be a costly addition to a pump, but can tremendously increase the versatility of a pump. In PD pumps, speed is directly related to flow rate. Particularly for wineries that plan to significantly expand operations in the coming years, speed control can allow them to gradually increase the capacity of a pump as demand rises. With less quantity to pump, winemakers will generally look for a slower flow rate in order to minimize damage to must and/or limit aeration. As the winery grows and a higher volume of must needs to be pumped, the winemaker might opt to increase the pump speed to quicken the pumping process. For all-in-one pumps, speed control allows the user to pump slowly for delicate tasks such as must pumping but then amp up the flow rate for later fluid-only transfers such as barreling. There are three major forms of speed control:
Depending on the supplier and quality of the pump that you are looking to buy, prices of must pumps can greatly differ. Pumps in the same category can have dramatically different prices due to different features and pumping capacities unique to each brand/model. The following list demonstrates an approximate order of must pumps from most to least expensive: