Thursday, October 28, 2010

pH issues with organic fertiliser

One thing that has really impressed me in Faugeres is the pH of our finished wines. In Australia and New Zealand I was always battling a pH that would blow out after ferment and MLF. Therefore a healthy dose of H2T was always needed to keep the pH around 3.60 in my finished wines. I would do this to ensure stability to the wine as spoilage bacteria and yeast would flourish at a higher pH especially if, heaven forbid, there was a little sugar left for them to chew upon.
Then we arrive in Faugeres and the first thing that I notice is that the pH of the juice is quite low even as we are picking at quite high potential alcohols (>16%). After fermentation the wines are around 3.40 and, taking into account that the Malic acid is very low, after MLF I am ending up with a very workable pH of 3.50-3.60. Perfect! But why and what will I do to the pH balance if we start adding organic fertiliser and messing with the terroir?

The uptake of nutrients is dependent on soil pH. The diagram below illustrates this commonly known data. The diagram shows that the optimal pH of soil is between 6.0-8.00 for maximum uptake of nutrients.

In hot climates, like the Languedoc, wine making is often difficult as the pH usually blows out. This is because malate will generally decrease because of respiration. The higher temperatures will also favour greater enzyme activity that facilitates the uptake of potassium which leads to an elevated pH (>3.50) due to the exchange of hydrogen ions from malate.

Wine scientist Bruce Zoecklein has also outlined some important parameters in potassium uptake that include soil type, rootstock, vigour, shading, crop level and seasonal variations. This leads me to think that tha schist soils of Faugeres somehow inhibit the uptake of potassium or the low levels of potassium in our soils are too low to satisfy the enzymatic uptake into the vines.

This is what we know from our 2010 harvest;

Vineyard # 1 Carignan La FiƩre

This vineyard is approximately 60 years old and is in goblet form. The soils are calcaire and predominately Marron. The soil pH here is a very stable 8.0 but the organic matter is very low as is the levels of phosphorus (<0.02g/kg optimum is 0.07-0.20) and potassium (0.108g/kg optimum 0.25-0.31.)The wine unfortunately was blended but still the pH was 3.46 before MLF, 14.51% alc/vol and 1.4g/L sugar.

Vineyard #2 Syrah La Espinasses

35 year old vines trained VSP. The soil is marron schist with a low pH of 5.80. Again the vineyard is lacking in Organic material and in phosphorus (0.031g/kg) and potassium (0.105g/kg). This wine went to barrel with a pH ~3.55 before MLF, 15.10 % alc/vol and 1.40g/L sugar.

Vineyard #3 Grenache Mas de Lanus

35 year old vines trained VSP. Marron schist with a 7.30 pH. The organic matter is healthy here but again the soil is lacking in phosphorus (0.030g/kg) and pottassium (0.059g/kg). Wine ph was a very low 3.39 at 80% MLF, 16.31% alc/vol, 1.30g/L sugar.

I will track these wines and report back on how they finish and more excitingly I will track what happens in the vineyards after we add fertiliser this year. What will be the change in the wine pH? That is the major question taht we will be investigating. Any thoughts or observations would be appreciated on this subject.

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