**2. Comparison of different methods for alcohol reduction**

There are several strategies available to produce wine with less alcohol. The most interventions take place before the wine status either in the vineyard, prior, or during fermentation (**Table 1**).

The strategies based on grapevine breeding and selection of clones as well as all strategies in viticulture are preventative and require a certain plan in advance. If, contrary to the assumption, the weather conditions for grape ripeness are very unfavorable, the desired maturity delay or reduced sugar storage in the berry is counterproductive.

In the field of microbiology, two different approaches are possible to produce less alcohol from the initial sugar present.

One possible way is to reduce the sugar content before fermentation by using the enzyme glucose oxidase. The glucose present in the must is converted to gluconic acid in the presence of molecular oxygen by the enzyme glucose oxidase (GOX). The challenge with this process is to reduce the oxidation of other constituents of the must and to reduce excessive acidity in wine [50, 53].

Another microbiological strategy is the use of special yeasts with lower alcohol yield. These yeasts usually show a higher content of fermentation by-products. Due to these other metabolites, the quality as well as the typicality of the wines produced may suffer. The use of genetically modified yeasts is probably seen as very critical by most consumers [60].

Also the metabolism of yeast can be rearranged by taking advantage of the so-called Pasteur effect. For this purpose, a yeast culture is kept in a solution with always less than 5 g/l of sugar. However, the control and addition of must has to be very precise in this process. Automatic measurement and control technology should help to facilitate this process for the user.

#### **2.1 Sugar reduction through membrane coupling**

Sugar reduction through membrane coupling can be seen as a unique technological approach for reducing elevated alcohol levels. Before problems arise due to excessive sugar levels in must, fermentation problems are prevented by a selective intervention. The sugar reduction of must is performed in two steps. Subsequent


**253**

retained.

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

treatment with ultrafiltration and nanofiltration removes sugar from the must. Consequently, the fermentation produces a wine with lower alcohol. This technology may help to prevent stuck and sluggish fermentations due to high sugar contents and consequently elevated alcohol levels. These high alcohol levels also have a

First membranes for ultrafiltration were commercialized in 1926 by membrane filter GmbH [1]. The surface of the membranes is porous, and the pore sizes in ultrafiltration are 10–1000 Å. The retained particles are usually 0.1–10 μm and larger. Common applications of ultrafiltration in food production are dairy processing in milk processing plants and clear filtration in fruit juice production. The use of ultrafiltration for protein removal is conceivable in winemaking [22, 23, 29, 62]. Nanofiltration was developed in the late 1980s. It has been described as a technique between ultrafiltration and reverse osmosis. Nanofiltration usually retains molecules such as sugars and organic acids. The pore size of the membranes is 1–10 nm, and the molecular weight cutoff (MWCO) is at 100–500 Da. The usual working pressure is up to 40 bar. Nanofiltration has many possible applications in winemaking. It is used to remove volatile acidity or to reduce the amount of malic acid. Nanofiltration is also used to concentrate must and wine. If nanofiltration is coupled with another process, the alcohol content of wine as well as the sugar

In this case the permeate of an ultrafiltration is separated in the first step. This fraction contains besides water, acid, and sugar only a few anthocyanins and tannins. During the second step, this fraction is concentrated by nanofiltration. The permeate of the nanofiltration contains then mainly water, some acids, and barely sugar. This aqueous solution is finally blended back to the retentate of the ultrafiltration. The sugar content of the must is thereby reduced after the treatment. The byproduct of that process is the retentate of nanofiltration. This fraction is viscous and high in sugars. The ratio of fructose and glucose is maintained because nanofiltration withholds equal amounts of fructose and glucose. Tartaric acid and potassium are retained only to a small extent, whereby the acidity and pH value are not or hardly changed. Anthocyanins and polyphenols are concentrated in the retentate of nanofiltration due to their molecular size. Consequently, they would be missing in the treated must. Therefore, it is important for red wine to perform the procedure before maceration. A "saignée" has to be done before fermentation. This fraction has to be clarified and treated by the two-step process to avoid color and tannin losses. This pre-clarified fraction is then reduced in sugar content and finally

The English-language literature contains various synonyms for osmotic distillation, such as membrane distillation, transmembrane distillation, capillary distillation, or pervaporation. Other sources also speak of isothermal membrane

In the process of osmotic distillation, two liquids are separated by a microporous, non-wettable membrane. Both fluids are directed along this membrane, with none of the fluids permeating the membrane pores. Only the volatile components present in the respective liquids can pass the membrane by evaporating and permeating through the pores of the membrane. This gas phases then go into solution of the other side of the membrane. Due to the hydrophobic nature of the membrane, water cannot penetrate the pores of the membrane. Thus, ions, colloids, and macromolecules that do not evaporate and diffuse through the membrane are completely

negative influence on malolactic fermentations [5, 49].

content in the must can be reduced [11, 16, 17, 19, 26, 40, 44, 57].

added to the original red wine mash [25, 26, 57].

**2.2 Osmotic distillation**

distillation [28, 36].

**Table 1.**

*Overview of strategies to achieve wines with lower alcohol content [57].*

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

*Advances in Grape and Wine Biotechnology*

during fermentation (**Table 1**).

less alcohol from the initial sugar present.

help to facilitate this process for the user.

**2.1 Sugar reduction through membrane coupling**

Early harvest at lower sugar levels

Adaptation by different training systems

*Overview of strategies to achieve wines with lower alcohol content [57].*

Canopy management like defoliation or shading

the must and to reduce excessive acidity in wine [50, 53].

counterproductive.

by most consumers [60].

**Grapevine breeding**

Clones with reduced sugar accumulation

New varieties with reduced sugar content

**2. Comparison of different methods for alcohol reduction**

There are several strategies available to produce wine with less alcohol. The most interventions take place before the wine status either in the vineyard, prior, or

The strategies based on grapevine breeding and selection of clones as well as all strategies in viticulture are preventative and require a certain plan in advance. If, contrary to the assumption, the weather conditions for grape ripeness are very unfavorable, the desired maturity delay or reduced sugar storage in the berry is

In the field of microbiology, two different approaches are possible to produce

One possible way is to reduce the sugar content before fermentation by using the enzyme glucose oxidase. The glucose present in the must is converted to gluconic acid in the presence of molecular oxygen by the enzyme glucose oxidase (GOX). The challenge with this process is to reduce the oxidation of other constituents of

Another microbiological strategy is the use of special yeasts with lower alcohol yield. These yeasts usually show a higher content of fermentation by-products. Due to these other metabolites, the quality as well as the typicality of the wines produced may suffer. The use of genetically modified yeasts is probably seen as very critical

Also the metabolism of yeast can be rearranged by taking advantage of the so-called Pasteur effect. For this purpose, a yeast culture is kept in a solution with always less than 5 g/l of sugar. However, the control and addition of must has to be very precise in this process. Automatic measurement and control technology should

Sugar reduction through membrane coupling can be seen as a unique technological approach for reducing elevated alcohol levels. Before problems arise due to excessive sugar levels in must, fermentation problems are prevented by a selective intervention. The sugar reduction of must is performed in two steps. Subsequent

yield

**Viticulture Microbiology Enology**

of sugar (e.g.,

oxidase)

Yeasts with reduced alcohol

Alternative metabolization

enzymatically by glucose

Membrane processes before fermentationSugar reduction by membrane

Distillation treatments(a) Vacuum distillation(b) Vacuum rectification(c) Spinning cone column

Membrane processes after fermentation(a) Osmotic distillation(b) Nanofiltration or reverse osmosis coupled with second treatment

coupling

**252**

**Table 1.**

treatment with ultrafiltration and nanofiltration removes sugar from the must. Consequently, the fermentation produces a wine with lower alcohol. This technology may help to prevent stuck and sluggish fermentations due to high sugar contents and consequently elevated alcohol levels. These high alcohol levels also have a negative influence on malolactic fermentations [5, 49].

First membranes for ultrafiltration were commercialized in 1926 by membrane filter GmbH [1]. The surface of the membranes is porous, and the pore sizes in ultrafiltration are 10–1000 Å. The retained particles are usually 0.1–10 μm and larger. Common applications of ultrafiltration in food production are dairy processing in milk processing plants and clear filtration in fruit juice production. The use of ultrafiltration for protein removal is conceivable in winemaking [22, 23, 29, 62].

Nanofiltration was developed in the late 1980s. It has been described as a technique between ultrafiltration and reverse osmosis. Nanofiltration usually retains molecules such as sugars and organic acids. The pore size of the membranes is 1–10 nm, and the molecular weight cutoff (MWCO) is at 100–500 Da. The usual working pressure is up to 40 bar. Nanofiltration has many possible applications in winemaking. It is used to remove volatile acidity or to reduce the amount of malic acid. Nanofiltration is also used to concentrate must and wine. If nanofiltration is coupled with another process, the alcohol content of wine as well as the sugar content in the must can be reduced [11, 16, 17, 19, 26, 40, 44, 57].

In this case the permeate of an ultrafiltration is separated in the first step. This fraction contains besides water, acid, and sugar only a few anthocyanins and tannins. During the second step, this fraction is concentrated by nanofiltration. The permeate of the nanofiltration contains then mainly water, some acids, and barely sugar. This aqueous solution is finally blended back to the retentate of the ultrafiltration. The sugar content of the must is thereby reduced after the treatment. The byproduct of that process is the retentate of nanofiltration. This fraction is viscous and high in sugars. The ratio of fructose and glucose is maintained because nanofiltration withholds equal amounts of fructose and glucose. Tartaric acid and potassium are retained only to a small extent, whereby the acidity and pH value are not or hardly changed. Anthocyanins and polyphenols are concentrated in the retentate of nanofiltration due to their molecular size. Consequently, they would be missing in the treated must. Therefore, it is important for red wine to perform the procedure before maceration. A "saignée" has to be done before fermentation. This fraction has to be clarified and treated by the two-step process to avoid color and tannin losses. This pre-clarified fraction is then reduced in sugar content and finally added to the original red wine mash [25, 26, 57].
