Tag: sulphur dioxide

Where all the fun happens…

This week we take a look at what happens inside the winery laboratory!

OK, “fun” might be a bit of a stretch, but for a science geek like me, it is!

Over the course of the last few months, as I have led you through some of the key steps of making wine, I have alluded to this placed called the “laboratory”. If you’re imagining a corner of the winery where geeky, glasses-and-white-lab-coat-wearing people spend their days playing with beakers and test tubes, well….. actually, you’d be pretty much spot on. However, if science (or learning about it) is your thing, it is one of the most exciting and fascinating places in the winery.

It is also one of the most important. The winemaker relies on data from “the lab” (that’s what all the cool kids call it!) to make key decisions during the winemaking process. What many people don’t understand is that winemaking is highly scientific. That’s where Rob, and his background as a (maths and) science teacher, comes in very handy and probably why he is so good at it. He understands the importance of getting things right.

So what happens in this place of wonder and awe?

There are a number of tests that the laboratory can perform during the lifespan of a wine… from pre-harvest of the grapes to bottling of the finished wine.

Let’s take a closer look at a few of the key tests…

Measurement of residual sugar

By now, you should be getting pretty familiar with this. Previously we’ve talked about measuring Baumé in grape juice to determine when the grapes are ready to pick. We’ve also looked at how the same measurement is used to determine whether the ferment is progressing and when it has finished. Considering this measurement is taken a few times before harvesting the grapes and then usually twice a day during fermentation, it’s easy to see that this is one of the most basic but important tools a winemaker has.

Without going into too much detail there are a number of instruments which can be used to take this measurement. If you are lucky enough to work in a laboratory which has a digital refractometer, then life is easy. Smaller wineries though rely on a piece of equipment called a hydrometer.

A hydrometer is usually made of glass, and consists of a cylindrical stem and a bulb weighted with mercury or lead to make it float upright. The juice or wine is poured into a graduated cylinder, and the hydrometer is gently lowered into the liquid until it floats freely. Hydrometers have a scale inside the stem, so that the person using it can read the Baume measurement.

Measurement of pH

If you can think back to your high school science days, you may remember a term called pH. It’s a tricky concept to grasp, but basically, it is a measure of acid in a liquid. Acids exist in different forms, and one of these forms is free hydrogen ions. pH measures the concentration of hydrogen ions, which are important in that they influence chemical reactions in the juice or wine. Concentrations of these ions in solutions are very low, so chemists invented a scale for expressing acid condition in all sorts of liquids (not just wine). This scale ranges from 0 – 14. Pure water is neutral at pH 7, lemon juice sits around pH 2 and grape juice and wine usually sits in the range of pH 3 – 4.

The thing to remember about pH in wine is that the higher the pH, the greater chance of oxidation. During the winemaking process, some of these free ions are used up through chemical reaction so the pH increases. Acid additions are often made with the aim of achieving an acid level which is in balance with the sugar, alcohol and fruit in any particular wine.

It’s a very delicate process, one which needs constant monitoring to ensure the levels are optimum. In the laboratory, pH is measured using a pH meter.

 

 

Testing sulphur dioxide levels

As we discussed a couple of weeks ago, the production and addition of sulphur dioxide is an important element in the process of making wine. It is also important to make sure the level of sulphur in the wine is just enough to help prevent oxidation, and at the same time keeping the level as low as possible.

This is a pretty involved test. I have included the below video for those of you who are interested. But be warned… it is of the educational, not entertaining variety. I won’t be offended if you don’t press play!

I could go on…

… and on, but I won’t (for now)! I’ll stop before I lose you all, but I may come back to the lab every now and then to chat about other important tests (unless I get a resounding “no! please don’t!” from you all in the comments section).

If you are particularly interested in this side of wine-making, please let me know via the comments. I’m happy to answer any questions you may have.

Our young wines are growing up…

While the hustle and bustle of vintage is finally settling down, there is still plenty of important working going on in the winery. Rob is busy preparing his ‘babies’ for the next stage of their development (and no, he doesn’t have a favourite!).

Let’s take a look a closer look…

Sauvignon Blanc (in tank)

This wine has now been confirmed in the lab as “sugar dry”. That means that fermentation is complete.  Therefore, it is now ready to “rack” (which will happen over the coming week) and a small amount of protective sulphur dioxide will be added.

Whoa… wait up! That’s a lot of technical terms to throw at you in one paragraph. Let’s just take a minute to look at these in more detail.

Sugar Dry:  This just means that all of the fermentable sugars (being glucose and fructose) are below 1 g/L (or 0.1%). There comes a point in the fermentation that measuring the Baumé is no longer sensitive enough to determine the point when the fermentation has stopped, and the wine is considered dry. That is when the laboratory needs to use much more specific tests such as enzymatic assays or High Performance Liquid Chromatography (HPLC for short, because let’s face it, that’s a mouthful!).

Racking: racking a white wine simply means to move it from the tank it was fermented in (with all the lees and sediment at the bottom of it) to a fresh, clean vessel. Particularly with a wine like Sauvignon Blanc, you don’t want to leave it on this sediment for too long after the completion of fermentation as this starts to affect the taste of the finished wine.

Sulphur Dioxide (or SO2): Let’s come back to this.

Chardonnay (in barrel)

This wine is also dry, so Rob is happy to add the malolactic bacteria now. He’ll then give it a good stir and top up the barrels to ensure there is very little space at the very top. The more space, the more oxygen in the barrel which has the potential to cause oxidation.

If you missed the question on last week’s blog post about why Rob prefers to wait until the end of fermentation to add the MLF bacteria, then here is the answer…

“There’s a feeling that adding MLF bugs while the yeast fermentation is still finishing (and residual sugar still in the wine), may lead to acetic acid (VA) production. Since there’s no great rush to get MLF started, we’d prefer not to take that chance!”

Fumé Blanc (in barrel)

This is also dry and will now be treated in the same way as the Chardonnay

Pinot Rosé (in tank)

Again, this one has also finished fermentation and is considered dry. It’s also ready for some MLF bacteria to be added. Seeing this wine doesn’t spend any time in barrel, and the malolactic fermentation process will happen in a tank, Rob will need to transfer this to a tank that is just big enough for the volume of wine and then top it up to make sure the amount of space in the tank is at a minimum… just like the barrels for the Chardonnay and Fume.

Pinot Dry Red (in barrel)

The Pinot has been dry for a while now. At least one of the barrels has already finished malolactic fermentation. Rob will give it a couple more days before he gets the lab to take a representative sample of all of the individual barrels to check if all of the barrels have finished. If they have finished, then he’ll rack them and add a small amount of sulphur dioxide and top them up.

Racking a wine in barrel is essentially the same process as for wines in tank. The wine is siphoned off into a tank, the barrels are then cleaned out with a high pressure hose to remove all the sediment and residue and the wine is then returned to the barrels.

At this stage, the wines are really quite fragile. That’s why it is super important to keep oxygen away from the wines by ensuring the containers are absolutely full. This means periodically checking all the barrels and topping them up as necessary.

So, what’s the story with sulphur dioxide?

Without opening an enormous can of worms, let’s briefly have a chat about the role of SO2 in wine production.

Sulphur dioxide has been used in winemaking for many years. There is talk of the Egyptians and Romans using it, but there hasn’t been any conclusive proof of that.

Sulphur dioxide is a unique compound which inhibits microbial activity and aids in preventing oxidation and therefore is commonly used for maintaining the wine in prime condition.

It can be added to the bins in which the grapes are harvested and transported to the winery, to the juice prior to fermentation and, most commonly, to the wine after fermentation and during storage.

Sulphur dioxide is added in very small amounts and is considered harmless to most consumers. A small proportion of people can be sensitive to sulphur dioxide. In these cases though, it is important to remember that sulphur dioxide is actually naturally produced by yeast during the fermentation process. Therefore, some sulphur dioxide will be present in all wines even if it has not been added.

Do you have any questions or comments about adding sulphur to wine? We’d love to hear your thoughts.