Wine Storage Guide

7 Golden Rules of Wine Storage

Temperature

In a nutshell: Wine should ideally be stored at 8 to 15°C, no warmer. If the wine gets warmer, the delicacy is lost very quickly, the wine loses its elegance, finesse and fruitiness and is simply no longer good. This process is permanent and cannot be reversed by chilling again.

But beware: the ideal storage temperature differs from the ideal drinking temperature. The following illustration provides an overview:

But back to wine storage: of all the criteria to consider when storing wine, temperature is the most important - but why is that?

The reason, and this is where a little physical biochemistry comes into play, is the temperature-dependent reaction kinetics of the many substances that naturally make up wine. And there are a lot of them - the biochemist counts well over 1,000. That many? Most of it is water, then come alcohol, methanol and glycerine as the most important by-products of fermentation, then the various acids (tartaric, malic and lactic acids in first place), the unfermented residual sugars fructose and glucose, the minerals, especially potassium, calcium and magnesium. Then it gets exciting: aromatic substances, higher alcohols, volatile acids, aldehydes, ketones, flavonoids, anthocyanins and a multitude of phenolic components (or tannins) of all kinds - in the milligram or even nanogram range, but it is often precisely these that are particularly important for sensory perception.

Compilation of the most important ingredients of wines:

These are all natural ingredients that either come from the berries or the juice (primary ingredients), are formed during fermentation and malolactic fermentation (secondary ingredients) or are only formed during ageing (tertiary ingredients). This complex mixture is instable - especially the sensitive, fine aroma components, the higher alcohols, the natural ketones, aldehydes and the numerous phenolic components react with each other and ensure that the wine is constantly changing in terms of its appearance, smell, taste and aftertaste.

When it gets warmer, the ingredients react more intensively with each other; when it gets colder, the reactions slow down. This fact is well researched and is described by the so-called Arrhenius equation or reaction rate-temperature (RGT) rule, also known as van 't Hoff's rule. It describes the dependence of a reaction rate constant on the temperature.

It goes something like this: Starting from 10 °C and a shelf life of 12 months, it can be simplified to say that the reaction rate of the ingredients with each other doubles to quadruples with every further increase of 10 °C - and thus halves the shelf life or reduces it to ¼. At 20 °C, the reaction rate is therefore twice as high as at 10 °C, the shelf life is only 6 months, at 30 °C it is at least four times as high, the shelf life is only 3 months, at 40 °C it is already ten times as high or higher, the shelf life is only less than 1 month. In addition, as the temperature rises, reactions take place that do not occur at lower temperatures. Therefore, at temperatures above 20 °C, the tasty aromatic substances in the wine are lost very quickly and, unfortunately, irretrievably.

Therefore: store your wines in a cool place, below 15°C, so that you can enjoy them for as long as possible. This can be in the fridge, in a wine climate-controlled cabinet or in a special wine storage unit with a controlled temperature.

Temperature Part 2: Temperature Fluctuations

As we have already mentioned, temperature is the most important factor in wine storage, but what we have not yet discussed are temperature fluctuations. While it is relatively insignificant whether the wine is stored at 10 or 16 °C, it is in contrast quite significant if a wine storage has, for example, 17 °C in summer and then 9 °C in winter over the course of a year. Temperature fluctuations greatly accelerate the maturation of wine and have a negative impact on wine quality.

Ideally, temperature fluctuations in a wine storage should remain below 6°C throughout the year!

This can be explained as follows: when it gets warmer, the wine in the bottle expands slightly: with 3 °C more, in a normal 0.75-litre bottle, this is 0.5 ml. An overpressure is created. The magnitude of the overpressure depends on the temperature difference. The following table provides an overview:

The table shows the pressure increase with rising temperature. Analogously, the pressure decreases with a drop in temperature. The pressure values are then identical, just negative, and indicate a slight to strong vacuum in the wine bottle.

If the pressure difference is less than 100 mbar, a negligible pressure increase can be assumed. Between 100 and 200 mbar of pressure increase, the influence is slight. If the pressure increase due to the temperature change is between 200 and 400 mbar, a significant influence can be assumed. If the pressure exceeds 400 mbar, it can be assumed that the cork moves. In the opposite case, i.e., with a vacuum in the bottle, it can be assumed that the vacuum is balanced by gas diffusion into the bottle - the cork will not move. It is precisely this process, in which the vacuum "sucks" air into the bottle, that introduces new oxygen into the wine, accelerating aging and enabling reactions of wine components that negatively affect wine quality.

The table clearly shows that the residual air volume in the wine bottle has a very large influence on the internal bottle pressure. Winemakers now strive to keep the residual volume in the bottle as low as possible - around 6 ml is the average. The following rule of thumb provides an indication of how to roughly estimate the residual air volume:

1 ml of residual air in the wine bottle corresponds to approximately 0.3 cm in the bottle neck.

Then to the pressure increase. The pressure increase can also be calculated by yourself, the formula is relatively simple. First, the volume increase due to the temperature difference of the wine is determined:

The volume increase of the residual air volume is then determined in the same way:

The pressure increase is then calculated from the two volume changes:

If the temperature in the wine storage rises, there are two possibilities: if there is still some residual air in the bottle (which is usually the case), the expanding wine compresses the remaining air more and thus compensates for the volume increase. If this is not or only very slightly the case, the pressure becomes so great that the expanding wine pushes the cork out of the bottle a bit - the overpressure is thus reduced. The reason is simple: air can be compressed relatively easily. Liquids, however, cannot.

The smaller the residual air volume, the sooner a temperature increase will result in the cork being pushed out. This can be only a few millimetres to a centimetre – depending on the magnitude of the temperature increase.

So far, so good. But if it gets colder again, the volume of the wine decreases again – creating a vacuum in the bottle. Since the cork has a certain air permeability, the pressure equalization in this case almost always occurs through air diffusing into the bottle through the cork. This is easier than moving the cork further into the bottle. The vacuum equalizes slowly. However, new air (and thus oxygen) enters the bottle through the cork in this process. The cooling bottle literally sucks in the surrounding air. This gives the wine additional oxidation potential, accelerating the reaction of wine components: particularly disadvantageous is the introduction of new oxygen into the wine, as this leads to reactions of wine components that negatively affect wine quality – and which would not occur without it. It is precisely these that have a very detrimental effect on wine quality. The result: the wine ages faster than it would without temperature fluctuations, and its quality deteriorates. The temperature fluctuation thus acts like the bottle breathing, and each temperature fluctuation acts not only like an accelerator for the aging speed of the wine but also deteriorates the wine quality. Therefore, maintaining a very constant storage temperature is so important.

And what to do if it has happened? It is best to enjoy it immediately, as long as the aging and deterioration processes have not yet begun.

Humidity

The ideal humidity for wine storage is between 45% and a maximum of 65% relative humidity. This is important even though humidity is completely irrelevant to the wine it-self. If it becomes too dry, it can cause a problem with the cork, which loses its elasticity due to dryness. A dried-out cork allows more air exchange, causing the affected wine to age faster. However, the problem of corks drying out is rather rare, as most corked bottles have a capsule that additionally protects the cork from drying out. For wines with a screw cap or synthetic cork, excessively dry storage is not an issue.

High humidity is more often a problem in wine storage

From 70% relative humidity, the growth conditions for mould fungi become increa-singly favourable, and from 80%, they are ideal! Mould fungi infest all organic materials, including wood and labels. If a wine cellar is too humid, the labels are covered with black spots or become unreadable within a few weeks. Wine bottles with such labels are disfi-gured, or it is impossible to tell which wine it is.

And what if the cork has mould?

This can happen - but it is not a problem. The fungus grows on the cork but stops as soon as it encounters alcohol that has diffused from the wine side of the cork into its depths. This stops the mould from growing further. As seen clearly in the image below, no metabolic products of the mould are found on the cork in the wine. Therefore, before opening a bottle with a mouldy cork, wash and scrub it with hot water, dry it, and then pull the cork. By the way, if the cork is old and brittle, it is best to use a two-prong cork-screw.

What does "relative humidity" actually mean?

First of all, humidity is the weight proportion of water vapour in the air. The matter of humidity is a bit complicated because the warmer the air is, the more water it can absorb. At 0°C, it's about 5 g in 1 m³ or 1,000 litres of air; at 10°C, it's about 10 g in 1 m³; at 20°C, about 17 g in 1 m³ - and so on. To have a temperature-independent measure of humidity, the relative humidity (abbreviation r.H.) was created. It expresses the percentage of air saturation with water, making it a better indicator than the absolute water content of the air. 70% relative humidity means that the air has absorbed 70% of the possible amount of water. The following table and chart illustrate the relationship.

Some wine storage rooms naturally have high relative humidity - typically these are cellars whose surrounding soil is moist and transmits this moisture to the room. To protect such rooms permanently from high humidity and associated mould infestation, either structural renovation or continuous air treatment with a dehumidifier is recom-mended.

Cool wine storage areas (whether cooled or naturally cool) into which warm air constantly penetrates (e.g., when entering) or which adjoin warm rooms, can also cause a mould problem. This is a known issue with wine storage in restaurants. What happens here? Two factors come together: as the warm air, which can hold more water, cools, the relative humidity rises, suddenly making water available for mould spores (from 70% r.H.), and mould growth begins.

The problem of condensation

During this process - warm air with high water content entering cold rooms - the dew point is undershot by the cooling (the dew point is the temperature at which the air is 100% saturated with water). The water condenses and becomes visible as water droplets. Everyone has experienced that a cold wine bottle, taken dry from the refrigerator and placed on the table, becomes wet after a few minutes. Water condenses wherever the temperature-related water saturation of the air is exceeded. This phenomenon occurs wherever the dew point is undershot. The fogged-up wine bottle is just one example; ty-pical spots are all areas where the transition from warm to cold is significant, such as the wine rack itself and the wall. These spots are usually hidden in rooms, less visible, and of-ten real breeding grounds for mould. This makes a room very unhygienic and un-healthy!

Condensation can also occur over large areas, such as on glass wine racks. Such fog-ging can ruin the beauty of a glass wine rack used as a display area.

For this reason, we offer our air-conditioned glass cabinet VITRUS and glazed design wine climate rooms. These products ensure that your wine collection is optimally stored without condensation affecting aesthetics or promoting mould growth.

Humidity, mould, and health

Mould not only destroys wine bottle labels and infests all organic materials, including the wood of wine racks, but it also poses a health problem. The following table provides an overview, sorted by the colour of the mould.

High humidity in the wine cellar (as in all rooms) should therefore also be avoided for health reasons.

Possible controls and remedies

Controlling humidity is simple; the measuring devices are inexpensive. To reliably avoid these humidity-related problems in wine storage, a well-designed air conditioning system combined with guided air circulation is the solution of choice. Why? Because air conditioners in air-conditioned rooms always produce drier air than would naturally oc-cur. This is because, as the air passes by the evaporator of the air conditioner, it cools be-low the set room temperature, reaching the dew point, and water is expelled. Thus, an air conditioner always acts as a dehumidifier (or water trap) and ensures a relative humidity of between 40 and 60% in air-conditioned rooms, the ideal range for wine storage. If the air from the air conditioner is then specifically directed to the critical condensation points in the room and warmed, the air can absorb water again, and such a wine storage room remains mould-free and the glass does not fog up or clears up after just a few minu-tes.

If the humidity problem in the wine cellar is not so severe, simple means like cat litter can help, as cat litter absorbs water from the surrounding air and stores it so that it is no longer available to microorganisms. From time to time, the water must be removed from the cat litter material: the best way to do this is on a hot summer day outdoors.