Grape juices containing high levels of grape solids can result in increased hydrogen sulfide production during primary fermentation. However, excessively clarifying juices may result in fermentation difficulties. Attenuated or stuck primary fermentations resulting in elevated levels of volatile acidity may occur.
Well says wine making text 101. While there is a lot to be said about wine making 101. For Winemaking 101, previous work by the (AWRI) has revealed that fermenting on grape solids also results in significantly more polysaccharides in white wines. This is due to more than extensive skin contact, using pressings, and even more than partially fermenting white juice on skins. Higher levels of polysaccharides are thought to positively contribute to white wine mouth-feel. Polysaccharides also 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 never say we have plenty of time, it’s vintage”. We don’t say this. Adding pectolytic enzymes achieved fast clarification. Adding enzymes, which within minutes, ‘mulch down’ the juice polysaccharides that inhibit settling. This hastens clarification. Alternatively, settling grape juice can be sped up by adding bentonite as its charged surface helps to agglomerate grape solids into heavy particles which precipitate more easily.
Meanwhile, the AWRI investigated the effect of different types of juice clarification (natural settling, enzyme and bentonite assisted settling) on the macro-molecular composition of white wine.
Clarification methods and the time taken to achieve various levels of clarity are being investigated. Polysaccharide, protein and phenolic composition levels are also being investigated by AWRI. For more information about fermentation of our wines, please contact me by email in the first instance.