Enzymes are natural and fundamental elements in the winemaking process. Although they occur naturally in wine grapes and yeast, commercial enzymes are commonly found in many modern-day wineries. They can be used to improve extraction and the aromatic profile of a wine, while also accelerating the winemaking process.
Enzymes are basically proteins that speed up the chemical reactions during winemaking. Commercial enzymes are very much like cultured yeast strains being derived from natural sources and the majority of commercial enzymes fall into one of two categories: those that aid in extraction and those that increase volatile aromatics.
The first group of enzymes are known as pectinases and includes pectin lyase (PL), pectin methyl-esterase (PME) and polygalacturonase (PG). These are predominantly used on red varieties, it breaks down the cell walls of the red skins, while extracting anthocyanins and tannins, which improves colour intensity and stability.
Pectinases also provide a number of other technical advantages: they accelerate the pre-fermentation stages, increase free run juice yield and enhance settling, clarification and pressing. This all leads to an overall improvement in the grape must quality, with increased aroma and polyphenol concentrations.
Glycosidase enzymes work to maximise the aromatic potential of a wine in a shorter amount of time, by increasing the concentration and speeding up the process. These enzymes enhance aromas by releasing aroma compounds bound to sugars in the odourless glycoside form. The release of bound aromatics also occurs naturally in wine by means of acid hydrolysis, albeit at a much slower rate.
Desirable aroma compounds such as terpenes, which are aromatic and floral, are usually sought to be enhanced, while others, such as phenols which are often associated with a medicinal or barnyard character, is best avoided. The treatment will therefore be most suitable to aromatic white varieties high in terpenes, such as Riesling, Muscat, Gewürztraminer and Viognier.
β-glucanases have traditionally been used to improve filtration of wines obtained from grapes infected with Botrytis cinerea. This fungus secretes glucans into the juice during infection which could lead to filter clogging.
β-glucans are the main component of yeast cell walls and aside from the abovementioned activity, they can also be used to enhance yeast autolysis. Natural yeast autolysis is a long-term process that occurs for more than 12 months after fermentation. Commercial glucanase containing enzymes facilitate improved yeast autolysis through a reduction in time, as well as an increased quantity of released yeast cell wall compounds.
Secondary enzyme activity
The nature and composition of the growth substrate used to produce enzymes induces the production of a wide pool of enzymatic activities.
As a result, the main activity in the obtained enzymatic product is accompanied by numerous secondary, or side activities that play roles of varying degrees of importance in winemaking applications.
Some side activities might have an undesirable effect in certain cases and a positive effect in others. Although these side activities are tolerated under the legislation, these enzymes can in certain cases spoil a wine’s quality.
Hemicellulase and cellulose side activities are present in varying amounts in pectinase preparations. They are wanted in red grape maceration in order to extract the maximum skin cells content, but are unwanted in white grape maceration to limit over-extraction.
Cinnamyl esterase contributes to the hydrolysis of hydroxycinnamyl-tartrate esters in white wines. This activity releases coumaric and ferulic acids, which lead to the formation of vinyl-4-phenol and vinyl-4-guaiacol; these compounds give unpleasant poster-paint and nail polish smells. In red wines, vinyl phenols react with polyphenols to form colour-stabilising compounds.
Anthocyanase activity releases anthocyanins from their bound sugars and could thus cause a colour loss in red wines, resulting in an unstable anthocyanidin form.
When and how to use enzymes
During white winemaking, settling and skin contact enzymes can be used. After crushing, negatively charged pectins form a protective layer around positively charged grape solid particles, keeping the particles in suspension. Pectinase enzymes break the pectin molecules into smaller components, exposing some of the positively charged grape solid particles underneath the protective layer.
These bind to the negative charges of the pectin protected grape solids to form bigger particles which settle out. Settling enzymes work mainly on the soluble pectins of the grape’s pulp, the skins contain more insoluble pectin (protopectin), with more side chains. Therefore, in addition to the basic settling enzyme components, skin contact enzymes contain more side activities that specifically work on the side chains of the pectin.
Skin contact enzymes are highly concentrated and contain essential side activities, which improves juice and aroma extraction. Grape cell walls form a physical barrier between the juice in the vacuole of the berry and the outside medium. Pectinases helps to break this physical barrier, increasing the juice yield.
Most grape aroma compounds and their precursors are located in the grape skins and the process of skin contact increases their concentration
in the must. An adapted white skin contact enzymatic formulation contains reduced levels of cellulases and hemicellulases, which prevents over-maceration.
Red winemaking maceration enzymes can contain hemicellulase for improved maceration. These enzymes should also contain very low levels of anthocyanase activity, which breaks off sugar units from more complex molecules. Maceration increases the anthocyanin content; however, the more important action of enzymes used on red grapes is the increase in colour stability.
When ageing wine on its lees, yeast autolysis takes place. This has many advantages for the wine quality, such as increased mouthfeel acquired from the polysaccharides that are released into the wine.
Certain mannoprotein fractions improve protein stability, while others improve tartrate stability. Some components released into the wine during autolysis can also have an impact on wine flavour and complexity. To achieve true yeast autolysis within three to eight months, a commercial glucanase-containing enzyme can be used.
However, autolysis releases many amino acids and nucleotides into the wine that are a source of nutrition for organisms such as bacteria
and Brettanomyces. In the case of malolactic fermentation, this can be advantageous, but if a cellar is contaminated with Brettanomyces, then the enzyme should best not be used.
Production and formulation
To produce the enzymes used in winemaking, selected strains are cultivated in fermenters under aerobic conditions. These include Aspergillus niger for the production of pectinases and β-glycosidases and Trichoderma harzianum in the case of β-glucanases.
Enological enzymes can be formulated in either liquid or micro granulated form. Micro-granulate enzyme preparations offer good storage stability and at room temperature, the shelf life ranges from 24 to 36 months.
Liquid enzymes should be stored at a cold temperature in the shelf life of these products, when stored under recommended conditions, ranges between 12 to 24 months. Their microbiological stability is more difficult to guarantee and their formulation often requires the use of preservatives.
Timing is everything
Commercial enzymes not only speed up the release of aromatics, but also reduce maceration time and accelerate settling and clarification.
However, the use of enzymes on the wrong grape variety or at the wrong time may have undesirable consequences, such as producing off-flavours or masking varietal typicity.
The timing of enzyme addition (and the amount added) is usually instructed by the manufacturer; the majority of enzymes are added just after the grapes are crushed, to the juice or post-fermentation.
With an increased focus on ‘natural’ winemaking around the world, the use of commercial products such as enzymes, which is said to contribute to ‘homogeneity’ in the wine world has become a concern for some. However, when used with the correct grapes, at the opportune time and for the right reasons, commercial enzymes can assist winemakers in realising the ultimate potential of their products.