Bentonite is a clay, impure hydrated aluminium silicate, and is found only in a few places in the world. The most suitable for wine comes from Montana and Wyoming.
The clay (around 0.5g/L of wine ) is hydrated in approximately 5 times its weight in hot water and left to swell for 12 to 24 hours. By that time it forms a thick thixotropic paste.
A little wine is gradually added to the paste to form a slurry which is then added into the Semillon and mixed thoroughly.
This addition has the affect of the bentonite adsorbing the proteins in the wine by either by electrostatic attraction or by hydrogen bonding. Bentonite is negatively charged, the wine protein positively. This is another case where chemical addition activity is dependant on wine pH. The lower the pH the more positive is the protein molecule charge.
While the initial muddy look of the wine can be a bit disconcerting to the uninitiated, in a few weeks we will be able to rack the clarified wine off the settled residue layer.
The Pinot Noir came in at 11.3 deg Baume and pH 3.4 after a full block test on 17th February ie. not ripe.
This was a bit of a surprise as it has not 'progressed' too far from a few weeks ago. Maybe the 50mm of rain had more of a dilution affect than expected. So it is still a waiting game.
As expected a quick test of the Cabernet resulted in 10.0 deg Baume.
The Tempranillo needs another week or so before its first racking ie. siphoning the clear wine off the solid residue that will have formed on the bottom of the tank after the egg white fining addition.
And just when you think you have all the pests covered, I found around 5 satin bower birds in the Cabernet. As the vines are completely enclosed in netting I went looking for a hole and found at least 6 right on the bottom of the net where it is pegged into the ground. Satin bower birds, our major bird pest, are very cunning and will walk around the base of the netting looking for a way in. I have even seen them trying to lift the netting with their heads in an attempt to get entry.
Our other bird pest, the currawong usually clambers over the top and sides. It has a long beak and can swing back and forth on the nets and take a peck at a bunch on the inward cycle.
A little further investigation found that these holes are being made by rabbits (scrapings and poo evident ) who must be anxious to get at the fresh green grass shoots of the mid rows and are chewing their way through the nets. We are now baiting the area.