Uses of R.O.
Reverse Osmosis is a type of filtration for which several wine production applications are currently being explored. It differs from all other types of filtration in that the filtrate ("permeate") which passes through the filter membrane, does not contain the color and flavor of wine. The wine's vinous character is retained in the unfiltered portion ("retentate").
If you are an experienced wine producer, a common experience when you begin your first reverse osmosis application is that it may be disconcerting that the filtrate is obviously stripped of vinous character. It takes time to realize that unlike all other filtrations, the product is not the filtrate; it is the retentate!
Permeate, which has the appearance of water, passes slowly through the filter. The filter is so tight that it would plug almost instantly in a normal pad filtration format. To prevent this, large flows of wine are recirculated across the filter surface to scrub the membrane and preclude fouling. This strategy is called "crossflow filtration."
Small molecules in wine may pass through an R.O. filter preferentially according to their smallness. Since H2O is the smallest molecule in wine, all of the other constituents are passed into the permeate in lower concentrations than are present in the wine. A typical permeate stream might contain water plus ethanol (75% of retentate concentration), acetic acid (60%), ethyl acetate (40%), and lactic acid (15%), and little else. Since the effective cut-off molecular weight for significant passage is 100 daltons and ions do not pass at all, R.O. permeate contains substantially no tartaric, citric or malic acids, anthocyanins or other phenolics.
Depending on what the winemaker desires to accomplish, this permeate stream may be simply discarded, or may be treated to remove a particular constituent and then recombined with the retentate. The result may be a wine with the same volume and constituents except that a specific element has been reduced, enhancing the perception of desirable flavors. All R.O. applications seek to remove "surgically" a low-molecular-weight constituent of the wine with as little change in the rest of the wine's composition as possible.
Development of valuable uses of this capability is ongoing. Current commercial uses include volatile acidity reduction, alcohol adjustment, and juice concentration for rain water removal. Units can also purify water. Ultimate applications may include sulfide removal, cold stabilization without refrigeration, and flavor concentration.
R.O. separation can be a powerful tool to improve wine quality, when employed in an integrated system of well-conceived wine production strategies. Side benefits are also being continually discovered. For example, reduction of volatile acidity and/or alcohol has been proven an effective aid to restarting many stuck fermentations.
RO MODEL CHARACTERISTICS
Packed-Column Permeate Distillation SystemsVinovation's patented approach of packed-column distillation of reverse osmosis permeate is the world's most widely employed method for alcohol adjustment. A powerpoint presentation of the method as presented to the OIV Groupe d'Expertes in Paris in 1999 is available through Contact Us.
Intrinsic advantages over other methods:
1. Wine color, flavor and tannin remain in the tank. Only colorless, flavorless permeate is submitted to distillation.
2. Tailored size to need (5 to 100 PG, or 10 to 200 liters of pure alcohol), and easy portability of smaller units.
3. Extraction of 180oProof high-purity ethanol results in product shrinkage of 1.3% per percent reduction in the wine, compared with 2.1% reduction with vacuum distillation.
4. Applicability of R.O. to other uses such as juice concentration, wine concentration, and (for small lots) V.A. reduction.
Wine sensory aspects
An important aspect of our experience with this work is the existence of discrete points of harmonious balance or "sweet spots." Mysterious as it is, we generally find that a 0.1% difference in alcohol causes a significant alteration in the sensory properties of a wine. For this reason, in the "traditional" practice of beet sugar addition to the fermenter (chaptalization), the buried assumption is naive that any resulting alcohol within a general range is adequate to balance the wine.
Often two or three "sweet spots" are located by a sensory panel, with different wine styles from which the winemaker may choose a preferred wine to market. Sensory trials supporting this finding from experiments performed at CSU Fresno are contained in the OIV presentation.
Still design and economics
We are the leading manufacturer of packed-column stills for use on RO permeate from wine. This unique application (permeate contains no solids nor precipitables) allows our stills to accomplish 30-plate purification in two meters of column rather than the normal 15 meters, and to employ column cross-sectional areas one third of a normal continuous still. This accounts for the economy of our designs, which result in capital costs a fraction of other designers.
Our stills range from 5 to 100 PG's per hour. Since a PG is a half gallon of pure alcohol, this corresponds to alcohol reduction capability of wine from, say, 14.8 to 13.8%, at rates of 250 to 5,000 gallons per hour.
Small stills have different economics than large stills. For the range of 5 to 20 PG's per hour, it is usually wise to use an electrical immersion heater as a convenient energy source, and to plumb glycol to the condenser. A 10 PG unit, for example, would use 26 KW of electrical energy (31 Amps per leg of 3-phase 480V), and 8 tons of refrigeration. Small operations which accumulate no more than 120 gallons of distillate on site at a time are subject to less stringent fire protection requirements. For larger stills, the energy consumption outweighs design simplicity, so steam energy (usually at most half the cost of electricity) and direct water cooling (10% of capital costs and 1/6th the energy consumption) are more sensible.
Labor for all stills is the same. A semi-skilled operator is employed during operation, who can be trained in a day to operate to perhaps 80% of the efficiency of a seasoned operator. Since the wine is not present, there is no danger of damage to wine quality. Labor savings is a major attraction of larger stills.
We advise clients interested in still purchase to first rent equipment from us in order to acquaint themselves with details of operation and assess proper sizing.
On-site distillation is not for everyone. Many of our clients prefer to own their own R.O. and ship us permeate for distillation at our site and return. This approach may be used in the U.S. even in Estate Bottling situations if only permeate is shipped.
Once you have digested this information and can give us an idea of your requirements, we will provide quotations for an appropriately-sized R.O. and still for your requirements.
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