A fascinating article about monitoring vineyards just before harvest. After reading it you will begin to learn just how much work goes into making great wine!
As grapes ripen, the winemaker monitors sugar levels, acidity and flavours. The colour intensity of red grapes can also be monitored using a spectrometer.
Initially the winemaker needs to sample the vineyard. The sampling technique can vary from berry samples or bunch samples taken evenly across the vineyard (for example, sample every ninth vine and choose a bunch closest to the centre of that vine). The sample is crushed by hand and the grape juice is separated from the skins. At this stage we call the grapes berries!
“There is a lot of chemistry involved in winemaking! We’ll bring you a lot of this information and more through our newsletters as you learn about the world according to Simall Wines” says Simon Hall, Simall Wines winemaker.
The sugar level is monitored using a hydrometer that floats in the juice sample. In Australia and France the unit for measuring the sugar level is Beaume (pronounced ‘bow-may’), where one Beaume is equivalent to 1% alcohol after the yeast have fermented it. The United States of America uses Brix to measure sugar levels and Germany uses Oechsle. Each of these scales effectively measure the same thing but using a different scale. Who knows why each country uses a different scale – perhaps they believe that their scale is the best but Simall Wines believes that Beaume is the best scale to use ?
Acidity (titratable acidity) is measured using a pH meter by taking 10ml of the grape juice sample and titrating it with 0.1M of sodium hydroxide to a pH of 8.2. The amount of sodium hydroxide used is multipled by 0.75 to get the measure of titratable acid. PH and TA results are used together to help indicate the grape ripeness and if the grapes will continue to ripen.
The table below contains examples of the typical sugar and acidity level of white grapes :
| Beaume | pH | TA | Comments |
| 11.0 | 3.10 | 12.50 | Grapes still unripe |
| 12.5 | 3.40 | 8.80 | Perfect, pick them tomorrow! |
| 14.0 | 3.80 | 5.70 | Grapes too ripe |
| 11.0 | 4.00 | 4.50 | Sugar level still low but the acidity tells us that the grapes won’t ripen anymore |
When the grapes are still unripe, they can be left for longer on the vine if the weather is going to be fine. The main weather concern is a prolonged period of heavy rain (4-7 days).
When the grape chemistry is perfect we want to pick the grapes as soon as we can.
If the grapes are too ripe (usually as result of a hot dry weather spell) the grapes should be picked. The wine will need an addition of tartaric acid to bring the pH down to around 3.40. This helps the wine become microbial-stable, improves the red wine colour and helps gives the wine length.
If the pH and TA indicate that the grapes will not ripen then they need to be picked anyway and acid will need to be added. The issue with adding acid is that wine can become unbalanced. We prefer to pick grapes with perfect chemistry and consequently make no adjustments to the wines chemistry. However, with weather playing a big part in grape ripening this cannot always be the case.
The final and important thing to consider just before harvest is the taste of the grapes. We look for a nice fresh fruit flavour in the grapes. For example peach melon flavours in Chardonnay or raspberry and plum flavours in Shiraz. Sometimes the grapes have great chemistry but very little fruit flavour.
Seeds are another indicator of grape ripeness, so we chew the seeds to check for any bitterness. We also look at the seeds to make sure they are completely brown. If they are green then the grapes are not ripe.
All of these checks occur from mid January which is when we start to consider grapes for harvest. It is then time to check the weather and if it’s fine we leave the grapes for another week and recheck then.