“Asoleo” or Sunning the Grapes

Before more scientific techniques were developed, the drying of fruit under the sun was an ancient technique by which the likes of dates, figs and grapes could be preserved. The history of this process goes back millennia but was probably introduced to Spain by the Moors who valued raisins highly as foodstuffs and used them in their cuisine.

Pasas or sun-dried grapes

In winemaking the technique was used to increase effective sugar content in the grapes thereby increasing potential alcohol, or simply producing much sweeter must.  It does, of course, reduce the amount of liquid. We all know that PX and Moscatel grapes are dried out in the sun- or raisined - to lose some of their water content and thus increase the proportion of sugars for sweet wines, but it used to happen with all the grapes as the Palomino produces a fairly low alcohol, low acid must. Indeed some Palomino is still dried, as in Lustau's Anada 1997.

A redor de esparto. Those used for pressing have a central hole. (foto:gentedejerez)

The newly picked grapes were collected in a canasta (a wicker harvesting basket) or a wooden pannier or nowadays in a plastic box but all with a similar capacity of 11-12 kilos (roughly one arroba) and laid out on “esterillas” or “redores de esparto” (esparto grass mats) of @ 80 - 100cm diameter in the sun of the “almijar.” This is an Arabic word meaning a large flat area of ground or yard suitable for laying out the grapes, usually in front of the vineyard building which housed the “lagares” (treading troughs) and overnight shelter for the harvesters. The time spent “asoleando” depended on the weather at harvest time. If the grapes were not ripe enough to produce enough sugar for @ 15%/vol alcohol in a dry wine, a day or two of sunning would correct that.  If it was intended to produce a sweet wine, a couple of weeks were needed to bring the sugar content up to the desired @ 500g/l.

The old way: sunning the grapes in the almijar of Palomino & Vergara

After one day the grapes lose about 10% of their weight (mostly water) and so the sugar content will be proportionately higher. Overnight the grape bunches are covered to avoid the risk of rehydration and potential rot from the dew, and the next day they are turned over to even out the sunning. The proportion of malic acid and, to an extent, tannin will be reduced, while that of tartaric acid will increase.

“Yeso” (gypsum =calcium sulphate) used to be added – and occasionally still is – perfectly legally, in the proportion of about 1-2 grams per kilo. This will help the wine fall bright and give the must a little more acidity. This ancient process is known as “plastering”, and while Victorian doctors ranted about its supposed deleterious effects on the wine, it is in fact perfectly harmless in reasonable proportions and is allowed under European law for wines produced in hot places where they have lower acidity. Most bodegas now simply correct the acid level with tartaric acid however, and no longer practise  malo-lactic fermentation.

The modern way: the hoops support overnight covering (foto: Consejo Regulador)

Using the asoleo method, the potential alcohol level in the grapes was sufficient for stability of the wine for domestic use, but export wines needed a bit more to withstand the rigours of a long sea journey, and were fortified as well. It was noticed that fortification killed off any flor allowing Amontillados to be produced more quickly, and that light fortification of Finos would save the labour involved in sunning grapes not destined for sweet wines. Accordingly only grapes for sweet wines are now sunned, and generally in the vineyard itself on long sheets of polythene which can be easily covered overnight.

Typical PX/Moscatel hudraulic press (foto: dimobe.es)

After two weeks of sunning the grapes will appear much darker and will have dried out to half their original weight, making it impossible to extract the juice in a normal press. A purpose-built hydraulic press is therefore used onto which a “sandwich” of esterillas and dried bunches will be placed. The hydraulic ram exerts much more pressure, and eventually a thick, concentrated, syrupy aromatic juice flows out. This will be allowed to partially ferment before being fortified, and after years of ageing it will be more concentrated still.

PX oozing from the press (foto:clubdevinos.es)

See also: Vinification in Jerez