With the recent hot weather it is important to consider the potential increase in phenolic compounds occurring in the skin that may have a negative affect if left in the grape must, writes Mark Crumpton, Berlin Packaging. Non-traditional and low intervention strategy is important, for example, using alternative yeast strains ZYMAFLORE® KHIO and ZYMAFLORE® ÉGIDE for biocontrol is an exciting new field that can lead to brighter, fruit-forward and fresher wine styles whilst reducing SO2 inputs. Oxygen is a highly reactive element that also needs to be treated carefully. The information below outlines the importance of treating the easily oxidisable compounds at the must stage that in turn make your life easier during the wine making process. 

Advantages of fining in must rather than wine, improving both aroma and colour

  • Oxidisable phenolics (mainly Flavanoids and phenolic acids) can affect colour by turning brown. These brown oxidised phenolics can scavenge important aroma compounds. 
  • Fining during fermentation may prevent aroma and colour modification by fining out oxidisable phenolics early on.
  • Each wine is unique and will require a tailored combination of fining agents suitable for the desired wine style.
  • CO2 from the fermentation will not protect phenolics from oxidising.
  • Time from grape to bottle – there is often less time to stabilise colour; greater need to fine.

The most common timing for fining is in the juice stage or in wine, but a multitude of research supports fining during fermentation as a beneficial practice. Fining is a generic term for removal of a particular set of compounds, and there are various methods to accomplish this. Combinations of fining agents can have a targeted effect on undesirable compounds without affecting nitrogen levels. Both micronutrients and nitrogen can be replaced through the addition of organic nitrogen sources, but key aroma compounds like thiols are lost indefinitely if they are not protected from oxidisable phenolics early on in the juice stage.

Wine is a complex matrix of proteins, colloidal matter, sugars, acids, phenolic compounds. Fining removes unwanted components from the juice or wine. This may be for the purpose of clarification, removal of oxidisable and non-oxidisable compounds which can affect colour, bitterness and other off flavours. Fining can improve the wine stability in a number of ways and improve the wine from an organoleptic point of view. Besides having a clarifying effect, fining leads to changes in the polyphenolic structure of wines and in red wines improves the stability of colouring matter by eliminating particles likely to precipitate later in bottle. Fining also helps reduce the microbial load of the wine.

What are the key aroma compounds that need protection? 

Thiols are a key part of expression in many varietals, the most notable being Sauvignon Blanc. Thiols are relatively unexpressed in grape juice but develop via yeast metabolism during alcoholic fermentation. The yeast strain plays a critical role in the formation of the thiols from precursors found in grapes. 

Methoxypyrazines are grape derived and important contributors to “green pepper”, “asparagus”, “grassy”, “herbaceous” and “vegetative”. These aromas are not modified by the fermentation, and were shown to be present even after oxidative handling in the absence of SO2.

Monoterpenes are plant derived, have characteristic floral, fruit, citrus odors in the form of geranoiol, linalool, nerol and alphaterpineol, and are present in aromatic muscat varieties. Terpenes are normally glycosylated and non-volatile in their glycoslylated form. These may be released over the course of the fermentation or with commercial enzymes.

 Esters, higher alcohols and volatile acids are produced exclusively by microbial intervention (this level is subject to genera, species and strain variation). Esters are much less prone to oxidation than thiols and can contribute fruit aromas.

Types of fining agents 

Fining agents can be divided into two categories: proteinaceous and non-proteinaceous. Their interaction with wine compounds can be in the form of a chemical bond, absorption and adsorption or electrostatic interaction. A chemical bond formation will bind to the compound in question and normally precipitate. Absorption and adsorbtion carries no electric charge and captures the compounds upon its structure. Electrostatic interactions involve the fining agent and the compound having opposite charges and attracting, the larger molecules which combine the fining agent will settle out.

What are the benefits of fining in juice rather than fining in wine? 

The removal of oxidisable phenolics are key to preserving aromas and importantly preventing the wine from oxidising and turning brown. Elimination of the phenol acids and flavonoids prevent the formation of o-quinones (brown compounds). If the majority of compounds that can be oxidised are taken out then there is much less to oxidise. Apart from changing the colour, o-quinones can then react with thiols, rendering the bound thiol inodorous thereby removing important aroma. 

When the must is fined rather than later on in the wine, the oxidisable phenolics can be removed before any impact on aroma and colour is caused. When fining wine, the oxidisable phenolics present may already have had an impact on aroma and colour and the rate used has to be much lower, as the fining at this point may have a much harsher effect. Glutathione is found in yeast and juice and can play a role in aroma protection via means scavenging oxygen and can bind to the oxygen in o-quinones forming a stable compound. During fermentation a fining agent is able to be kept in suspension due to the agitation caused by the fermentation, and as a consequence can be thoroughly distributed throughout the must. With the introduction of cross flow filtration, it can be tempting to skip the fining stage. Cross flows can make the wine clear, but not stable. 

What happens when wines aren’t fined? 

With the tendency towards producing a more ‘natural’ product with minimal intervention, some producers are skipping the fining stage. Aside from possible ramifications with colour and aroma, fining takes away harsh, astringent phenolics, often giving the wine a ‘phenolic’ palate. As discussed previously, fining in the wine is often too late, as the fining agent will have a much harsher impact on desirable compounds. Rosé colour will drop out if there are oxidisable phenolics present which aren’t taken out via fining, which leads to colour instability in tank and bottle.