Sherry wine

Vinification

Olga Nikandrova and Denis Shumakov.

If two extreme procedures of the sherry vinification technology — harvesting and bottling — ignored, the rest part of the technology may be divided into two parts. The second one being ageing and maturation of the wine in the Criaderas and Solera system. And the first one — everything preceding this ageing and maturation. First of all it is making the base wine. Such a division has not only academic character — it exists in reality (for instance in the form of bodegas with very narrow specialization) and is stipulated by the legislation which distinguishes Production Zone and Ageing and Maturing Zone in the Jerez Region.

It is noteworthy, that, as a rule, sherry technology descriptions pay most attention to the maturation of sherry in the “Criaderas and Solera” system. It is quite understandable since this maturation scheme is specific and landmark sherry technology. Notably less attention is paid to wine making procedures preceding maturation, which is, once again, explainable, but not quite fair.

We consider it necessary to get acquainted with this purely viniferous part of sherry technology chain — at least for the sake of “completing the picture”. Besides, despite the fact that sherry maturation and ageing system has a very strong “leveling” effect, its outcome critically depends on the quality of the materials used for maturation.

It’s important to note though that many of the mentioned below technological procedures may involve different equipment and be carried out in rather different ways. So, it is advisable to add “for example” or “most often” or “usually” at arbitrary places of the text while reading it.

Now then. The technology of making wine (wanted to introduce the term “pre-criadera preparation” but decided not to produce unnecessary matters) for its further conversion into dry sherry is very different from the technology of making wine for sweet sherry — which is natural, taking into account that the raw material (fresh Palomino for dry sherry, and raisined Pedro Ximénez or Moscatel for sweet ones) as well as the conceived outcome are also different.

Base wine for dry sherry

Let’s start with dry. Here is the list of operations (and tasks that are solved during their realization) which guide the conversion of grapes into wine that will turn into dry sherry after maturation.

• Weighing and analyzing (control of the yield and quality characteristics of the grape).
• Destemming (grape stalk separation, optional).
• Crushing (opening the grape skin).
• Pressing (making the must, first selection of the ageing type).
• Clearing the must (separating the juice from solid matters).
• pH-correction (acidification, biological protection).
• SO₂ treatment (delaying the onset of fermentation, preventing enzymatic darkening and bacterial “cleansing”).
• Racking (new solids separation, final biological “cleansing”, preparing the must for the special yeasts introduction).
• Addition of fully fermented must — pie de cuba (accelerated start of fermentation, introduction of the yeasts).
• Alcoholic fermentation (making wine).
• Racking (removing solids made up of yeasts and other matters).
• Analyzing the wine (final decision on the ageing type).
• Fortification (preparing the wine for ageing and maturation).
• Additional clarification (wine stabilization, finishing the work on wine which is now ready for the ageing process).

It’s easy to see that making wine for its further conversion into dry sherry has a lot in common with white wine vinification. The most outstanding distinctions being the absence of a procedure for malolactic fermentation and no cooling during alcoholic fermentation. Nevertheless the result of a certain part of abovementioned procedures can hardly be classified as anything else but white wine. But this is not very important though, what’s important is to clear up the technological procedures in detail.

The collected grape (it’s about Palomino grape, which has very tender berries with thin skin) is brought to the vinery as soon as possible. It is then weighed there and analyzed as to their ripeness degree and the health of the berries. Ripeness is characterized by acidity and density of the juice. Ripe Palomino’s acidity is low: pH 3,7 — 4,0. The juice density allows forecasting the alcoholic content of the wine (the higher is the density, the more sugar there is, and the more sugar — the more alcohol there will be after fermentation).

As was mentioned already, maximum yield should not exceed 10,5 tn per ha, and the grape juice density shouldn’t be less than 10,5° Baume — these values are set and controlled by the Regulatory Council, where apparently someone must be fond of the figure 10,5.

After being weighed and analyzed, the grape undergoes crushing. This tough word denotes rather a gentle procedure of opening the grape skin. If berries where not previously destemmed (full or partial destemming is optional in sherry making) then crushing is made very carefully not to crush down the stalks, so that substances that they contain wouldn’t penetrate into the juice.

After crushing, berries with opened skin and running juice undergo pressing, which is done in several stages. First extraction (primera yema, approximately 65% of total must volume) is done with the pressure of up to 2 kg per cm^² (the pressure of the grapes’ own weight). Second extraction (segunda yema, about 23% of the total must) uses the pressure of up to 4 kg per cm^². Finally, the third extraction (mosto prensa, all the rest) is obtained with the pressure over 6 kg per cm² — with the use of screw-type presses, for example.

The first extraction must contains more (in comparison with the following extractions) sugars and less polyphenols, potassium, iron and solids — and is better suitable for biological maturation. The second extraction must is better for oxidative ageing. While the third extraction must is not used for sherry production, but can be used to make vinegar or distillate.

The freshly extracted must undergoes a complex of procedures designed to prevent its fermentation and bacterial contamination as well as improve its aroma. First of all, the must is filtered through a mesh to separate it from stalks, pips and skins. Then it undergoes pH-correction — through addition of either tartaric acid or (following old traditions) gypsum. Higher acidity (which is the purpose of pH-correction, it is brought to the level of pH 3,1-3,4 being initially at the level of pH 3,7-4,0 ) protects the must against bacterial contamination during fermentation.

After pH-correction the must is treated with SO₂ (60-100 mg per liter, depending on the grape condition). Such a treatment creates additional protection against bacterial contamination, prevents enzymatic darkening of the must, impedes development of unwanted yeasts and delays the onset of fermentation for about 24 hours. During this time the must is cleaned off the solids and unwanted yeasts by means of racking, which enhances the quality of the wine (if racking is not overdone) and creates favorable conditions for the addition of specially selected yeasts.

All these procedures done, the must is placed into fermentation containers (previously, this employed 500-liter butts, nowadays — 50 000-liter stainless steel tanks bedangled with controlling and regulating equipment), where different, already fermented, must (pie de cuba) is added in the amount of 2 to 10 % of the total volume. This “injection” speeds up the onset of fermentation, decreases the chance of unwanted microorganisms’ growth and (optionally) involves specially selected yeasts (selected by their alcohol and acetaldehyde performance, resistance to sulfur dioxide and stability of the fermented wine’s acidity) into the work on the must.

Alcoholic fermentation consists of two stages. The first one (tumultuous fermentation) lasts from three to seven days and is characterized by intensive transformation of almost all sugars into alcohol, formation of glycerol, acetaldehyde, lactic and succinic acids, aromatic compounds, release of carbon dioxide, and generation of heat. It all happens at 23-26°C — such conditions are the most comfortable for the yeasts. The second stage — slow fermentation — is similar to the tumultuous one by biochemistry, but it passes in a notably less intensive way and doesn’t require temperature control. Its duration depends on the amount of the sugars left in the must and usually takes several weeks. The total duration of fermentation (both tumultuous and slow) is normally about 12 weeks, all other stages of wine making take much less time.

On the completion of alcoholic fermentation the young wine (it is already wine, indeed) is left to settle — to rack it off the lees (dead yeast and solid fractions, consisting mostly of tartaric acid salts and insoluble proteins). The cooling, which accompanies the opportune coming of late autumn, helps rapid settling of sediments. By November 30 (St.Andrew’s Day) the residue is removed. Then the wine is analyzed “attributed” to a certain maturation type. The finer wine (which consists mostly of primera yema must) will be used to produce biologically-aged sherries. More robust wine — sherries of oxidative maturation.

It’s interesting to note that after racking off the lees, the wine (base wine or mosto) comes out to be more than drinkable. It is a popular winter drink of the Jerez Region often called simply grape juice — despite its relatively high strength (10-12°). Such a sweet countrylike deception.

One more interesting (and more important) thing to note is that during the racking or decantation on the surface of the wine a layer of special yeasts, capable of active vital functions even after other yeasts have “eaten up” almost all sugar, starts to form. This is velo de flor — the very special yeasts which determine the characteristics of certain sherries which are aged under its layer. By the way, flor consumes residual sugars, glycerol and ethanol — the quality that makes one feel envy and sympathy towards it.

After the lees are racked off the young wine is fortified with grape distillate — to 15,5° for biologically-aged sherries (Fino, Manzanilla) and to 17-18° for oxidatively-aged sherries (Oloroso). Given the initial strength of the young wine, not so much distillate is required. This fortification results in new sediment, which is also removed. Besides, the wine is usually deironed, which makes it more stable. At this stage of vinification the product is ready for ageing.

Fortified and clarified young wine ready to run in the Criaderas and Solera system designated for biological ageing is called Sobretabla. And fortified and clarified young wine ready to run in the Criaderas and Solera system designated for oxidative ageing is called Añada (this term has other meanings as well). Sobretabla and Añada are kept in stainless steel tanks or other containers (at least one year, until the next harvest) and are taking from there in small portions to refill criaderas.

Making sweet sherry wine

Some words about sweet sherry now. Making the base wine for its further conversion into sweet sherry look laconic comparable to the abovementioned procedures which precede the ageing of dry sherry.

• Sun drying (raising the sugar concentration).
• Pressing and extracting the must.
• Stabilization of fermentative activity.
• Racking and separating the sediments.
• Fortification (preparing the wine for ageing).

Pedro Ximénez (if it is to be used in producing sherry wine) is collected later than Palomino — already overripe, with about 16°Baume sugar density. After harvesting the grapes are spread on special mats (often made of Esparto grass) for sun drying where they spend seven to fifteen days. Every day during sun drying the grapes are turned over and unhealthy berries are removed. In districts close to the ocean the drying grapes are covered for the night to avoid dew.

As a result of sun drying the grape looses water, changes color (darkens), becomes more dense, viscous and sticky, gains characteristic sweet sherry aromatic notes; its sugar content raises up to 400-450 g per liter.

After sun withering the grape is transported to the press — where certain difficulties arise. Dehydrated grapes are very hard to press. It is possible to smash them to pieces with a powerful press — but it is gentle extraction that is needed, which does not damage seeds or extract anything unwanted from the skins. That is why the dried grape bunches are layered separated by the grass mats on which they were sunned and accurately pressed in the vertical press. The mats help evenly distribute the pressure and delicately extract the juice. Which, obviously, comes in very small amounts — 25-30 liters from every 100 kg of grapes.

The collected must has a very high sugar content and little water, and on the whole everything is bad from the yeasts’ point of view. много Therefore, alcoholic fermentation starts there reluctantly and proceeds very inertly. For the must not to behave like a grape syrup which has suddenly got sour a little grape distillate is added into it, raising its total alcoholic strength up to 10°. The introduction of the distillate stabilizes the must — and it is left to settle in autumn and winter.

After settling the mixture of the must with alcohol (it is often referred to as wine, but it sounds somewhat unconvincing) is cleaned off the sediments, fortified with grape distillate up to 15-17° considered ready for ageing. It is also suitable for immediate consumption, by the way.

The wine from Moscatel is produced in a similar way, with the only difference that Moscatel is often sun dried on plastic nets spread on the sand, which heats in the sun during the day and gives off heat at night, thus contributing to the process of grape withering. It is also worth mentioning that Moscatel’s larger berries do not get dehydrated so much as Pedro Ximénez’s ones.

It is remarkable, to our mind, that the must which is destined to become sweet sherry wine ferments very poorly. Unlike dry sherries, during production of which fortification only aggravates their own rather prominent alcoholic strength, in case of sweet sherries the alcohol content is almost completely provided by the added distillate.

Read next — Sherry Ageing.

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