Fermenting on Solids cont.
Fermenting white juices containing high levels of grape solids can result in increased hydrogen sulfide production during primary fermentation. However, excessively clarifying juices may result in
attenuated or stuck primary or malolactic fermentations resulting in elevated levels of volatile acidity. Well so says Winemaking 101.
While there is a lot to be said for Winemaking 101, previous work by the AWRI has revealed that fermenting on grape solids also results in significantly more polysaccharides in white wines – more than extensive skin contact, using pressings, and even more than (what many may consider a radical practice of) partially fermenting white juice on skins. Higher levels of polysaccharides are thought to positively contribute to white wine mouth-feel, and to enhance both protein and cold stability resulting in less bentonite fining and lower refrigeration costs.
While juices will naturally clarify under the action of gravity given time, commercial vintage logistics dictate that the settling process be achieved as quickly as possible (“We have plenty of time – it’s vintage” is a phrase never said). Typically faster clarification is achieved by adding pectolytic enzymes, which within minutes, ‘mulch down’ the juice polysaccharides that inhibit settling. Alternatively, settling can be sped up by adding bentonite as its charged surface helps to agglomerate grape solids into heavy particles that precipitate more easily.
In a new project, the AWRI is investigating the effect of different types of juice clarification (natural settling, enzyme and bentonite assisted settling) on the macromolecular composition of white wine. The effects of the method of clarification and the time taken to achieve various levels of clarity on the polysaccharide, protein and phenolic composition are being investigated now.
For more information about fermentation of our wines, please contact me by email in the first instance.