**3. Critical evaluation of different technologies for alcohol reduction**

The authors did several trials during the last years. The following subchapter will summarize and compare economic and user-oriented considerations [54–60].

#### **3.1 Sugar reduction by membrane coupling**

The reduction of the sugar content at must stage by membrane coupling has significant advantages in terms of later fermentation. Excessive sugar levels can be reduced directly before fermentation problems occur due to osmotic stress in the beginning of fermentation or toxic stress due to elevated alcohol at the end of fermentation. Furthermore possible stress for malolactic bacteria is reduced as well. Several trials showed that the treated lots started fermentation faster and continued the fermentation earlier and to a more complete extent.

The quicker and complete fermentation can be seen positive from an economic point of view, as the fermentation tank capacity can be used more efficiently. Moreover stuck and sluggish fermentations are clearly negative in terms of quality and economic consideration [5].

The batch treatment of ultra- and nanofiltration goes along with a certain labor need during harvest, which is in fact the most labor-intensive time during wine production. Possible automation and scale-up of such plants might help to overcome that disadvantage. This treatment could be interesting to be offered by mobile service providers. In that case no additional labor is needed, no investment is necessary, and the regular cleaning and storage of the membrane is needed.

Improper cleaning and storage over several months could cause off-flavors. Even with careful cleaning, membranes can develop an off-flavor from organic matter in the fouling layer. The application of membrane coupling appears more difficult than white wine. The ultrafiltration as the first step of the treatment requires a certain clarification level; otherwise the membranes get clogged. If red mash should be treated, a careful clarification is necessary. In that case a "saignée" is made. That subset is clarified and can be treated. During that time the remaining mash remains with a high content of solids and due to that oxidation and microbiological spoilage can cause later problems. After the membrane treatment, the liquid subset is blended back.

Compared to other treatments for alcohol reduction, the sugar reduction goes along with relatively high volume losses. The reduction of 17 g/l, which corresponds to approximately 1 vol.% less alcohol, means a volume loss of 7% from the initial volume. A further useful application of the nanofiltration retentate could be the sweetening of other wines. Even with a sugar content of 500 g/l, care must be taken to ensure sterile storage. Unlike treatments to remove alcohol, this technology is not in conflict with regulations for distillation.

**259**

*Alcohol Reduction by Physical Methods DOI: http://dx.doi.org/10.5772/intechopen.85989*

Osmotic distillation is a technically simple approach to partial alcohol reduction. Membrane contactors are used in the wine industry in numerous processes such as aeration and degassing of wine. These membranes are more and more widely used by many manufacturers for the preparation of wine and semi-sparkling wine. Such systems are usually based on a membrane contactor with a membrane area of

. Depending on the equipment and the degree of automation, the costs for such systems are quite low. Simple systems with manual control valves start from approximately 7000 €. The durability of the membranes highly depends on the care of the membranes and is thus an important factor determining the economic efficiency of the plants. With proper cleaning and storage, the membrane contactors, which are the main cost of the equipment, can be used up to for 5 years before being exchanged by a new membrane. So the method of partial alcohol reduction can be used inexpensively in many businesses. The treatment by the osmotic distillation for alcohol reduction is relatively easy to perform if significant parameters are considered. The amount of previously degassed strip water must be limited to avoid harming the wine quality too much during the treatment. It is advisable to circulate the strip water in a closed and inert system. In many trials it could be shown that an alcohol reduction by 8 g/l should go a long with 14% of the wine volume as strip water. This proved to be the ideal compromise between a quick and aroma-saving

In order to prevent membrane fouling, the wine to be treated should first be

The work required to clean and preserve the membranes can be compared to that of conventional cross-flow filtration. Nevertheless the hydrophobic property of the membranes does not allow backflush or use of cleaning enhancers and

The alcohol reduction by osmotic distillation is continuous and needs little or no supervision during treatment. If the alcohol reduction is to be carried out close to the maximum permissible limit, it is advisable to reduce a portion of the alcohol content strongly and then adjust the alcohol content precisely by blending with the

The performance of the alcohol reduction is not constant as the driving force; the vapor pressure difference between both sides of the membrane gets lower during the treatment. So the alcohol permeation rate decreases during the treatment. The strip water accumulates in the alcohol content. In the experiments, it had

Due to alcohol reduction, the density of the treated wine increases. During the treatment of larger containers, the change in density can cause certain layer formation in the tank. Before assessing the final degree of alcohol reduction, the tank has to be homogenized carefully. Without this mixing, it can lead to errors in the measurement of the alcohol content, and thus a wine may be treated in too high extent. Since the systems for osmotic distillation are relatively small and mobile, it is conceivable to perform such a treatment with a mobile plant. For this purpose, the wine does not need to be brought to a plant as is the case for common systems based on distillation-based processes. The treatment can be carried out

If alcohol is separated from the wine, a number of custom regulations might

(4–7 vol.%), and so it is not economically interesting to separate the ethanol further in another distillation process. The recycling of the strip water as brandy is neither

be affected even if the separated alcohol fraction is not very high in alcohol

economically interesting nor from quality aspects to be recommended.

subjected to a wine filtration of min. Separation limit of 5 μm.

alcohol contents between 4 and 7 vol.% [27].

**3.2 Osmotic distillation**

20 m2

treatment.

surfactants.

initial wine.

within the winery.
