C6H12O6 + yeast → 2 C2H5OH + 2 CO2
The grape juice is now wine.
The marc was then returned to the vineyard rows. The skins are rich in potassium and are a good source of fertilizer for that element as well as a soil conditioner.
A further pH test was performed and confirmed at 3.8.
We wanted to adjust it to 3.6.
To achieve this tartaric acid (a natural grape acid) is added to the wine.
There is no magic formula ie. add x grams H2TA to xx litres wine to reduce pH by 0.1 units due to the differing buffering capacity of different wines.
It is a matter of trial and error. And it has to be done gradually as deacidfication caused by too much H2TA is a pain.
So our initial addition was 1.0 g/L.
This resulted in a pH of 3.7 so we added another 0.5g/L which got us to 3.6.
To clarify the wine we use egg white. One white is slowly mixed into a 10% solution with water and 0.5% salt to help dissolve the protein. This is then thoroughly mixed into the wine. Within a few weeks the solids suspended in the wine will settle to the bottom of the tank and the clear liquid on top will be racked off.
We do not use oak barrels for storage and aging. Previously we have added oak mini staves to our red wine in order to impart an oak nose and flavour. This vintage we are trying out a powdered tannin product made from oak heartwood and gall. This addition is said to produce exactly the same oak characteristics to those extracted when aging wine in wooden barrels.
Meanwhile the Semillon is still fermenting. Ferment temperature is around 25 deg C which is a little too high for good quality white wine but as mentioned before there is nothing much we can do about that.
Suffice to say that the smell of the ferment in the 'winery' is wonderful.
Our last test showed that it is about 50% 'there'.
The rain event mentioned in the last post lasted for 3 days and dropped around 50 mm on us.
So that was pretty much the forecast.
The farmers out west got 50-100mm in places so that was good for them. They still need a lot more however.
Our next jobs are to sulphur and fine the Semillon after fermentation is finished and test the Pinot Noir to establish whether harvest is imminent.
We will now need to spray the Cabernet and maybe the Pinot depending on its condition after the rain.