February in the Tamar Valley, Tasmania

Verasion Netting Water Management

Verasion

During February the bunches of Pinot Noir grapes change colour from green to black over the period of about 3 weeks.

The time of harvest is approaching where all your work during the season will be rewarded with high quality fruit of optimum ripeness.

During this month you can monitor the sugar and acid levels in your fruit and plot these to determine the time of optimum ripeness.

 

 

 

Netting

Once verasion has started, you will need to net your grapes to keep interested birds away from the ripening fruit.

I usually do this in the first week or two of February.

Determining Ripeness

Ripe grapes suitable for premium table wines need a balance of sugar level,titratable Acids & pH.

For consistently good wine, you need to measure these 3 factors accurately.

Taste the grapes weekly so you can learn to associate certain tastes with changing levels in the measured factors.

Nobody interested in making excellent wine walks into the vineyard and by taste alone determines when their grapes are ready for harvest.

They are interested in knowing the numbers.

Brix

Sugar level is usually measured in degrees baling or Brix- it is the percentage of the sugar in the grape juice.

To measure this accurately you will need a wine maker's hydrometer.

The presence of sugar raises the specific gravity of grape juice above 1.000 which is the specific gravity of distilled water.

Therefore we can use a hydrometer that measures Brix to get sugar content.

These are found at wine making shops. Some hydrometers are Baume hydrometers.

I don't use these as there are complex conversions to undertake.

Take two separate 100 berry samples, each crushed, sieved, and measured with a hydrometer,

with their specific gravities averaged will give an accuracy of plus or minus 1 degree Brix for the grapes in your whole vineyard.

The berries should be selected from the middle of the bunches, taken randomly from the vines of the same variety,

avoiding end vines and obviously diseased or stunted bunches.

The samples should be lightly crushed and the juice sieved to remove any free-floating particles,

which would interfere with the reading.

Pour the juice into a graduated flask or the cover of your hydrometer so that the level will allow the hydrometer

to freely float off the bottom.

Read the level from the bottom of the liquid surface.

The juice will be attracted by the glass and raise up the sides slightly,

so always take the reading from the bottom of the liquid level. ( See diagram)

* unless specifically your hydrometer is calibrated to read on the upper part of the meniscus.

Check on the instruction of your hydrometer.

You can check the potential alcohol level of your grape juice sample here

Titratable Acidity

Acid balance is extremely important in wine.

Acids give crispness, brightness and thirst quenching qualities to wine.

If there is not enough the wine will be uninteresting and most likely deteriorate quickly.

If there is too much, it will be harsh on the palate and tart-not at all pleasant to drink.

Most of the acid in wine is tartaric, and some will be malic, with some tiny amounts of other kinds such as citric and lactic.

Grape acids protect the wine from growing spoilage organisms.

Acids in wine have an optimum around 0.60 to 0.80 for reds and 0.65 to 0.85 for whites.

Harvest is indicated at the time the acids come close to their optimum at the same time sugar comes close to its optimum.

In many cases the optimum for both sugar and acids will not be reached but there are "rules of thumb" for judging readiness for harvest.

"Titratable Acidity" TA is a measure of total acid in grape juice as expressed as the tartaric acid content.

Determining titratable acidity involves neutralising a predetermined amount of juice with an accurately measured standard alkaline solution of NaOH.

The point of neutralisation is determined by use of an indicator, usually phenolphalein.

To learn how to make a measurement of Titratable Acidity visit here.

pH

pH is a measure of free hydrogen ions in a solution.

It is related to acidity(TA), but differs from it in several ways, and the pH of grape juice may not be correlated with the amount of tartaric acid.

As with other measurements there are optimums: pH 3.1 or 3.2 for white grape juice, and 3.4 for reds.

We need to know the pH to an accuracy of 0.1 which requires the use of a pH meter.

These can be bought from wine supply stores or from electrical goods stores for about $50- $500 for the highly accurate ones.

You will use it frequently in wine making, so it is well worth obtaining one that is reliable.

I have a hand held meter that is accurate to +- 0.1 once it has been calibrated.

Use clear strained juice, as solid particles in the juice will distort the reading.

You will need to allow for temperature differences also.

The meter I have calibrates differences in temperature and adjusts the pH reading accordingly.

High pH in juice can lead to wine defects from spoilage organisms.

If the pH of your wine is high, it may be due to over ripe grapes or your soil may be too high in potassium.

High soil potassium is directly linked to high pH in the juice.

To correct high pH you can add small amounts of tartaric acid during the wine making.

Readiness for Harvest

During the last two weeks of March I regularly take samples of my grapes and measure sugar, pH and TA as explained above.

When sugar is in the range 23-25 brix and TA is in the range 6-8 Pinot Noir develops some intensely beautiful flavours if allowed to hang for another week or so.

If you get rain in this period harvest immediately, as the vines will take up the moisture and dilute your sugar levels.

You will then need to wait until they build up again and risk the danger of skins splitting and subsequent infection of botrytis or decimation by hungry European wasps.

Harvest time is always a nervous period in order to get the optimum levels in your fruit without compromise.

The seeds in your grapes should be now toasty brown in colour and the grapes should taste very sweet.

Water Management

Water management after verasion is very important.

Give your vines adequate water to keep them growing but never load the ground up with lots of water,

as it may cause the softening skins of the grapes to split allowing the entry of disease and wasps which seek the high sugar content.

Preparing for Harvest

Get out all your equipment and lubricate it for the new season.

Crusher/ Destemmer

Lightly lubricate all moving parts and sterilise using a solution of potassium metabisulphite:

56 gms dissolved in 3.8 litres of water makes a strong sterilent for wine making equipment.

Keep the solution tightly stoppered as it is highly volatile.

You should have plenty of ventilation when using this- preferably do it outside.

Sulphur dioxide is highly poisonous in high concentrations, so take care if using it inside.

Grape bins- sterilise

Snips- sterilise in methylated spirits prior to using in your vineyard- especially if you have used them for another purpose.

Fermenting vessels all should be sterilised before use as over time,

as these pieces of equipment are colonised by yeasts which may lead to unwanted fermentation at this stage.

Next Month:

Harvest Day

Care for Vines after Harvest

See In The Cellar for a full account of the wine making process.

 

 

 

 

 

 

This page was last updated on 21/01/2014