Tag Archives: temperature

The magic of yeasts

Yeast

Yeast

Yeasts are fungi, which play a vital role in wine production. The number of different species runs into tens or even hundreds of thousands, no one is quite sure. More than one may be used in fermenting the grapes, and this has a big influence on the wine produced. Yeasts produce aromatic compounds as well as alcohol and carbon dioxide.

What yeasts need to make them work
Yeasts need the right conditions to work their magic during wine fermentation:-

  • Temperature. They operate in a temperature range. Too low, and yeasts don’t function, too high and they are killed off. The grape juice may be actively heated or cooled to achieve this.
  • Nutrients. Sugar is the main one, but you need a source of nitrogen, which is provided by amino acids. Winemakers may add selected nutrients.
  • Alcohol level. Different yeasts work in different ranges of alcohol content.

Winemakers split yeasts into two main categories

  • ‘Natural’ or ‘wild’ yeasts. These are the yeasts which are present in the vineyard, and stick to the grape skins. They are also on the wine equipment. These indigenous yeasts give the wine a local character, a sense of place. The term ‘terroir’ is often used to express this.
  • Cultured yeasts. These are developed to introduce particular characteristics to the wine, or to make fermentation more reliable. Usually, the indigenous bugs will be killed off with sulphur dioxide, and then the grape must/juice will be inoculated with the cultured yeast.

What can go wrong with a ‘wild yeast fermentation’

  • Problems with starting the fermentation. The grape must/juice will contain a range of bacteria as well as yeasts, and these compete for the nutrients. You may end up with acetic acid (vinegar) rather than alcohol.
  • Inconsistency. A number of different yeasts may be involved during a fermentation, with some dying off at quite low alcohol levels, and others taking over. If a different yeast takes over, you can end up with a different wine than you anticipated.

Conclusion
There is no right or wrong answer about the use of wild yeasts, it rather depends on the market you are aiming at. Cultured yeasts will help to produce a consistent product, which is going to appeal to the big brands. Small producers may well enjoy the variability.

Drinking wine on an aeroplane – a disappointing experience

Wines are usually disappointing if you drink them on a plane. The circumstances are unusual, with conditions affecting both the wine and the drinker.

wines to drink on an aircraft

wines to drink on an aircraft

What is unusual about aeroplanes:-

  • Aircraft are pressurised at the equivalent of around 8,000 ft altitude, which is about three-quarters of that at sea-level.
  • Air-conditioning reduces the humidity to around 10%, much lower than most people are used to.
  • There is a lot of vibration.

Affect on the wine:-

  • Low pressure reduces solubility of gases such as oxygen and carbon dioxide, and this reduces the wine’s freshness.
  • Red and white wines are usually served too warm, which has a significant influence on the taste and smell.
  • Wine is rarely served in a decent glass, and this has a negative influence.
  • Wines can be severely shaken up, which doesn’t help.

Affect on you:-

  • The low humidity has a direct influence on your nasal passages, and hence your sense of smell and taste.
  • You also salivate less in conditions of low humidity. Saliva moderates astringent tannins in wine, so a wine appears more astringent than normal in an aircraft.
  • Flying is stressful and tiring, and all this affects your senses.

Conclusion

The conditions tend to suppress the fruit and sweetness of a wine, and enhance any harsh acidity and tannin. So, wines need to be carefully selected to compensate for this.

Bottle variation

Bottles of the same wine may taste very different, and variations increase as a wine gets older. In fact one bottle of a mature wine may be wonderful, and the next over-the-hill. Why?

different bottle sizes

different bottle sizes

The blend
Virtually all wine is a blend from different barrels or vats. If the mixing vat is not big enough to take all the wine, then one batch may well differ from the next. So, there may be a difference before the wine is even bottled.

Bottling
A particular wine may be bottled in batches rather than all at the same time. The fill levels, added sulphur dioxide, entrained oxygen, and gas injected above the wine may all vary at each bottling session.

The closure
Historically this was always natural cork. It is a fine closure, but every cork is different and will allow differing amounts of air to diffuse through. This causes bottles to mature at different rates. One big advantage of screwcaps is that each closure is the same.

Transport and storage
This is a major issue, and can completely destroy a wine.

  • Temperature – is covered in more detail by another post. If the temperature gets too high, the wine will be damaged, perhaps fatally. Cases of wine stored at different temperatures will mature at different rates.
  • ‘Lightstrike’ – damage by over-exposure to UV light.

Bottle size
The larger the bottle, the more slowly and gracefully a wine matures. This may just be because the gap between the cork and the wine is the same for a half bottle, a bottle or a magnum. Any air in that gap will be spread more thinly in a magnum than a half bottle, meaning that it will be oxidised more slowly.

Age of the wine
The older a wine, the more time there is for all these influences to take effect, and the higher the chance of one bottle being very different to the next.

Climate change and wine

There are plenty of climate change sceptics, but it is a fact that alcohol levels in wine are increasing, and some grape varieties ripen, where they wouldn’t have 20 years ago.

Why is alcohol level an indication of higher temperatures?
Higher temperatures produce riper grapes, which have more sugar. During fermentation, the sugar turns to alcohol, so more sugar leads to more alcohol. There is an associated decrease in acidity.

Some grapes need more heat to ripen

Some grapes need more heat to ripen

Different grape varieties prefer different temperatures
The diagram shows that some grape varieties need longer heat exposure to ripen than others.

  • If the temperature is higher than ideal, the grapes will ripen, but the wine will lack freshness and acidity.
  • If the temperature is lower than ideal, then the grapes won’t ripen properly, and the wine will be tart and acidic.
  • If the temperature is much higher than ideal, then the vine simply shuts down, and nothing happens.

Which countries are most affected?
Those at the current extremes of temperature for growing vines:-

  • Much of Australia and Spain, for example, have vineyards in regions with high temperatures. They will have to adapt to survive.
  • Countries further from the Equator with more marginal climates, such as England, will now be able to grow a much wider range of grape varieties.

What can the adversely affected regions do about it?

  • Plant different grape varieties, which are more tolerant of the hot weather.
  • Train the vine branches so that leaves physically shade the grapes.
  • Allow plants to grow between the vines, as this lowers the soil temperature, and there is less reflected heat from any stones.
  • Plant new vineyards at higher altitude.

The serving temperature of a wine is important

A wine’s serving temperature is probably the most important factor in your enjoyment. It won’t make a great wine out of an average one, but it will make the most of what you’ve got.

Red wine serving temperature

Red wine serving temperature

Serving reds at room temperature
The adage used to be – serve a red wine at room temperature. That was fine in the days before central heating, but now ‘room temperature’ is usually over 20ºC (68ºF) , which is just too high. Any red wine is just bland if it is too warm.

White wine serving temperature

White wine serving temperature

Serving dry whites straight from the fridge
A domestic fridge can get a bottle down to 5ºC (41ºF), if you leave it in there for long enough. At that temperature the wine will just numb the taste buds, and you won’t smell much either.

Serving sweet white wines
These should be served well-chilled, 8°C to 10°C, 46°F to 50°F, is a good guide. Lighter sweet wines can be served at even lower temperatures. Lower temperatures make sweet wines less cloying.

Serving sparkling wine
Freshness is important in a sparkling wine, so its temperature should be lower than a dry white. Serving straight from the fridge at a little over 5ºC (41ºF) is ideal.

The affect of ambient temperature
Once a wine has been poured, its temperature will quickly move to that of its surroundings.

  • If it’s a warm day, then start the wine at a lower temperature.
  • If the weather is cold, then serve the wine at the correct temperature – you can always warm it up in your hands.

The 20 minute rule
This is as simple a rule as you are likely to get. 20 minutes before a meal:-

  • put the red wine into the fridge.
  • take the white wine out.

Is there a perfect temperature for storing wine?

temperature and humidity recorder

temperature and humidity recorder

Wine is an organic living thing. The temperature a wine experiences can have a big influence on its quality.

So, is there a perfect temperature?
Time has shown that deep cellars in temperature parts of Europe are perfect for wine storage. A constant temperature of around 12°C (54°F) is ideal. A high humidity prevents the cork from drying out.

Increased temperature leads to increased reaction rates
Wine is a complicated mixture of chemicals, which react with each other. As the temperature rises, all of the reaction rates will increase, but some will increase more rapidly than others.

Increased temperature leads to new reaction products
As the temperature rises, new reactions will occur, which simply wouldn’t happen at 12°C. An example is the breakdown of aromatic chemicals in dry white wines. Unpleasant compounds are also produced.

Wines with low sulphites/sulphur dioxide
Natural wines with low levels of sulphites (sulphur dioxide) are increasingly popular. Sulphur dioxide serves two very useful functions:-

  • to limit oxidation of the wine.
  • prevent bacterial growth.

Both of these become much more of an issue as a wine’s temperature rises, and natural wines are particularly vulnerable.

Unfiltered wines
If the temperature gets too high, it is perfectly possible to restart fermentation . This causes plenty of problems.

What if the temperature is lower than 12°C (54°F)?
As the temperature decreases, the reaction rates slow down. So, a wine may not mature in the normal way, but at least it won’t go off. If a wine gets cold enough it may deposit white tartrate crystals, but these do no harm. The alcohol in wine depresses its freezing point, so it needs to be well below 0°C (32°F) before it even starts to freeze.

Conclusion
If you live in a climate where the temperature is above 25°C (77°F), and you don’t have dedicated wine storage, then please keep ALL your wine in a domestic fridge. You will have to remember to take the red out in good time before drinking it, but at least the wine will be in good condition.

Putting the fizz into sparkling wine

Sparkling wines are more popular than ever, as they are lively and refreshing. How are they made, and what produces the bubbles?

Champagne cork and muzzle

Champagne cork and muzzle

Where do the bubbles come from?
Sparkling wines have carbon dioxide dissolved under pressure . When the bottle is opened, the pressure is released and the gas starts to evaporate. Bubbles form on irregularities on the glass, or material suspended in the wine.

What if there are no bubbles?
The main reason for bubble-free sparkling wine is dirty glasses. There is nowhere for the bubbles to nucleate.

What is the gas pressure within a bottle?
Champagne usually has a pressure of around 6 bar – 6 x atmospheric pressure – at room temperature. Which is why you get a mess if you open a warm bottle. The pressure decreases rapidly as the wine is chilled, which is one very good reason for serving cold Champagne. Other sparkling wines have a similar, or lower pressure.

Where does the carbon dioxide come from?
When sugar ferments in the presence of yeast, it produces alcohol and carbon dioxide. The more sugar you have, the more alcohol and carbon dioxide is produced.

  • In most sparkling wine production, grapes are fermented to a still wine. Sugar and yeast are added, and the second fermentation produces carbon dioxide for the sparkle.
  • In some rare cases there is just one fermentation, and the carbon dioxide retained, rather than allowed to evaporate.
  • The cheapest way of introducing the gas is to inject it into still wine, but this produces a coarse result.
Stopper to keep the fizz in a bottle

Stopper to keep the fizz in a bottle

Producing bubbles using a second fermentation
Starting with a still wine, there are three main methods for producing the bubbles:-

  • The method used in Champagne, now generally known as the ‘traditional method’. Wine is put into a bottle, along with sugar, yeast and nutrients. This second fermentation produces carbon dioxide. The debris is removed, and the wine sold in the same bottle.
  • The transfer method, in which secondary fermentation is in a bottle, but the wine is then transferred to a vat, where the debris is filtered out. The wine is sold in a different bottle.
  • The Charmat or Tank Method, where the second fermentation is carried out in tanks. The wine is then filtered and bottled under pressure.

The quality factor
Quality sparkling wines undergo a number of processes and maturation to give the same depth and complexity as a fine still wine, but they also have the prickle of bursting bubbles on the tongue.

Preserving wine once a bottle is opened

Once a bottle is opened, most wine has a very limited life. All but very mature wine will improve for a while when exposed to the air, but over time all wine will oxidise and become unpalatable.

The best thing to do with a bottle of wine is to drink it all at one sitting. If you fail to do that, then there are several options for preserving it in good condition for a few days.

Refrigeration

Chilling any wine, including reds, will help to preserve them. All reaction rates, including oxidation by air, will decrease at low temperatures.

Vacuum systems

vacuum stopper

vacuum stopper

vacuum pump

vacuum pump

These pump air out of the bottle. The less air there is, the less oxygen is around to spoil the wine. The problem with hand-held systems is that you are likely to remove some of the desirable chemicals as well. Commercial systems claim to pump the air out more precisely, without affecting the volatile compounds in the wine.

Inert gas systems – hand-held

The gas cannister dispenses an inert gas on top of the wine; this is heavier than air and displaces it. Pouring wine from a bottle will agitate what is left in the bottle, and dissolve some more air into the wine. The inert gas will not keep the wine for prolonged periods, but it works well for several days.

Inert gas systems – commercial

These use an inert gas to force wine out of the bottle, and through a nozzle into a glass. No extra air is introduced into the bottle. Enomatic is the market leader, and their website provides more details. These systems allow restaurants, wine bars, and shops to sell wine by the glass, even if it takes weeks to empty the bottle.

Plastic film on top of the wine

A company called Wine Shield sells specially designed thin plastic film, which sits on top of the wine in a bottle. This aims to keep air away from the wine. I haven’t tried it, but it does sound plausible.

A simple and reliable approach

I pour wine into a smaller bottle, and fill it. Pour with care so as not to introduce too much air. Then stopper it and put it in the fridge. Depending on the wine, this is fine for a couple of days. It lasts longer if you squirt some inert gas above the wine.

Wine storage – what you need to know

Wine rack

A classic wine rack

Wine is alive, and there are two things which will kill or maim it in no time at all, they are direct sunlight, and temperatures above 25°C (77°F). Even if you are going to drink a wine soon after buying it, beware shops and restaurants where these conditions apply.

Light, aromatic wines are most susceptible, and heavy reds the least.

Sunlight has two harmful properties – ultraviolet light (UV) light, and radiation which heats what it shines on. UV light encourages the breakdown of many chemicals, and the oxidation of others. All this is bad news for the wine. Coloured glass provides some protection.

Temperature. High temperatures cause some chemicals to breakdown, and others to react rapidly. New and unpleasant compounds are also produced.

Avoid rapid changes in temperature as this can cause the cork to move within the bottle, and allow air in. This influx of air causes the wine to go off more quickly.

Ideal storage conditions are:-

  • Temperature:- 12°C to 13°C (54°F to 56°F).
  • Humidity:- 60 to 70%. If the cork dries out it will let air into the wine.
  • Horizontal:- the cork should be in contact with the wine, to prevent it from drying out.
  • Keep it in the dark. No sources of UV light or heat.