Fermenting on Solids
Duncan Harris at Harris Organic Wines ferments his white wines on partial “solids”, while most Australian winemakers ferment white grapes off solids, what does this mean?
Meanwhile, all red wine is fermented on solids as the skins and pips are retained in the fermentation vessel, during fermentation.
Fermenting white grape juices containing high levels of grape solids can result in increased hydrogen sulphide production during primary fermentation. However, excessively clarifying juices may result in fermentation difficulties. Attenuated or stuck primary fermentation resulting in elevated levels of volatile acidity may occur.
Textbooks on winemaking
Well says winemaking text 101.
There are plenty of textbooks available about fermentation.
Wine Analysis and Production by Bruce W. Zoecklein, Kenneth C. Fugelsang, Barry H. Gump, Fred S. Nury
While there is a lot to be said about winemaking 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.
Enzymes for fast clarification
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 macromolecular 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 the fermentation of our wines, please contact me by email in the first instance.