Grape Harvest Season is here, but as a winemaker, when do you pick? As a visitor, when do you visit to see the harvest?
This is one of the biggest decisions of the year for winemakers. Mere hours can decide the fate of there wine for this vintage.
Mainly you will be considering climate, sugar, acid and maybe even the biodynamic calendar (only harvest on fruit days!)
Grape Harvest Season – Climate:
The climate has an impact on your final harvest because any rain or if you have a hot day, this can take your grapes beyond their peak ripeness.
In hot climates like California, you will see most vineyards harvesting at night while the grapes are cool to maintain their flavors and aromas. If you want to learn more about this, here is what some winemakers say.
The other things you are looking for when harvesting is sugar levels and acid levels in your grapes. This is a balancing act within the grapes, as the acids convert to sugars as the grapes ripen.
If they become “overripe” then you are in the territory of ice wine, this is when the grapes start to shrivel and look like raisens.
If you are an old school winemaker, you may choose not to run any modern tests and stick with the traditional taste test. When the grapes taste good, it’s time to harvest!
However, newer winemakers may want to add more science to the mix. We definitely do.
Grape Harvest Season – Sugar Levels:
The sugar in grapes is measured in Brix and traditionally you will find
- whites are harvested at 21-26 Brix
- reds are higher, between 24 and 28
It really depends on the wine you are after. The higher the sugar in the grapes going into fermentation, the higher the alcohol in the finished wine.
To do this you will need a refractometer before the grape harvest season beings, or a hydrometer if measuring juice during or post-fermentation. Find out more about these instruments here.
Grape Harvest Season – Acid Levels:
Acid is never something I thought you would want in a wine, but if you’re going to make excellent wine, then you are going to befriend acid.
Acid has a big impact on the tasting profile of a wine. Specifically, after a drink of wine, it is the acid that makes your mouth salivate. If the acid is too low in the wine, then your wine will taste flat.
Acid also balances out the sugar. This is why people love to drink citrusy juices. They have high sugar and high acid, a nice balance!
As a winemaker, you will want to know that acid is measured in two ways pH and Total Acidity (TA) which is sometimes interchanged with Titratable Acidity since it is the prominent acid in wine
pH:
pH originates from the French as ‘pouvoir hyrdogene’, which means hydrogen power. This is because you calculate the pH in a substance by taking the negative log of the hydrogen atoms
pH is an important measurement in wine because it tells you about the microbial stability of the wine. Effectively, this means that it dictates how microbes grow in your wine.
Most wines fall between a pH of 3 to 4, which means wine is on the acidic side of the pH scale. The scale goes from 0 to 14, where 0 is battery acid strong, 14 is alkaline and 7 is your neutral water.
Wine being acidic is great because it means that pathogenic organisms cannot survive in wine and therefore it is fundamentally safe for consumption. This is why it was so useful back in Roman times.
Highly acidic wines would include Riesling, Chablis and Muscadet which could have a pH of 2.9. Whereas a hot, California cabernet might have a pH of 3.5
To measure pH is quite simple, all you need is a cheap pH meter and some calibration tablets. The pH meter can fall our of accuracy after a day, so the tablets work by dissolving in water at a known pH and thus you can reset your pH meter to match
It’s up in the air whether pH or TA has a greater impact on wine taste. From everything I’ve read I believe the best answer is that pH dictates keeping qualities while TA is a better indicator for flavor
In chemistry, a buffer would be the natural salts found in wine, and these ultimately change the pH but have no impact on the total acid in the wine
Grape Harvest Season – Total Acidity (TA)
Total Acidity is measured as the grams per litre in wine. The benchmark for this is 6-8 grams in the finished wine, where 9 is sour and 5 will taste flat.
As you are going about your wine making you will want to measure this and you can do this by titration.
- You can do this with a laboratory tool called a pipette which is used to measure a portion of wine into a flask.
- Next, you will also add standard sized amounts of an alkaline solution to the flask using another lab tool called a burette (specialized in exact amounts)
- Keep adding these doses until the flask result is neutral, which is called the ‘end-point’ in titration
How will you know the solution is neutral? Well this is where the chemisty from the movies comes in. You get to add an ‘indicator’ to the flask which will change colors when the mixture is finally neutral.
This can be a bit tricky with red wine, as it might be hard to notice due to the deep red color. I have no idea how to get around this, so please comment below if you have any tips!
How do you know how much acid you have in the wine then? Well it equals the amount of alkaline solution that was added to neutralize your wine mixture.
This is the total acidity of your wine and is crucial to understand before you start your fermentation. This is so that you can make any necessary adjustments as early as possible, since trying to do so later will be less effective.
Ultimately you can make an adjustment later on as well, so it’s better to get ahead of the game and make smaller adjustments at the beginning and end of the fermentation. More on this next post!
For now it’s prudent to understand that labeling this in the EU will need this labeled not as Total Acidity but as Tartaric Acid and the minimum needs to be 4.5 grams per litre (probably smart because it would be way too flat otherwise).