Sunday, 9 December 2018
Clarification and Stabilisation of Sherry
The “en rama” wines have without doubt aroused great interest in Sherry as they are as natural and as close as possible to how the wine tastes straight from the butt in the bodega. While no agreement has yet been reached on a precise meaning of “en rama”, it is generally taken to mean that the wine has not been “stabilised” to the extent that most commercial wines are - either not at all or at least much less so. Barbadillo were the first to launch en rama back in 1999, but many bodegas were hesitant to follow suit as they were worried about stablility, and when they did, they put legends such as “drink within a year of purchase” on the back label. So what is stabilisation? Put simply it is a range of processes which ensure the wine cannot re-ferment in bottle.
The first form of stabilisation was alcohol, used mostly for export wines. At home, wines were traditionally bottled in winter when temperatures were low and any solids were close to or at the bottom of the butt. The biologically aged wines however, have flor to contend with and are often bottled more than once a year, and in the past Finos and Manzanillas were filtered and fortified to over 16°. For export they were filtered and fortified to a safe strength of 18° or even 20° (about 30° proof under the old British system I grew up with). Nowadays however with faster transport and better understanding of stabilisation they can be shipped safely at 15°. Since many bodegas cannot afford the equipment for stabilisation, they have always sold their wine en rama, particularly in bulk, but without any need to say so, or had it contract bottled.
Stabilisation consists of a number of processes which ensure the wine reaches the consumer squeaky clean and fault free, but at the inevitable expense of some of its complexity. One of the natural constituents of a grape is tartaric acid, and while the content of it in the grape reduces as it ripens some remains, in fact it is the principal acid in wine. It plays an important role in contributing to balance, however should the wine be subjected to low temperatures for a spell, during transportation perhaps or warehousing in cold countries, it can form harmless potassium bitartrate ("tartrate") crystals which precipitate, leading the consumer to think there are pieces of broken glass in the bottle. To avoid this problem wineries filter any colloids out and then chill the wine to about -5°C, just above freezing point (for an aqueous solution with alcohol) for a few days to remove excess tartaric acid before bottling. This is known as cold stabilisation. The addition of more tartaric acid, a process known as “seeding” can speed up this operation as the crystals are attracted to each other, grow heavier, and precipitate faster.
Another problem is unwanted flor yeast which is unsightly and brings the (slight) risk of refermentation in bottle should there be any unfermented sugars. Normally micropore membrane filters made from cellulose are used to remove it, and they are available with various pore sizes from between say 1.2 – 0.45 microns (a micron is a thousandth of a millimetre) depending on the type of wine. The smaller the pores, the more sterile the wine becomes. Another filtration medium which is occasionally used is activated charcoal which is good for organic impurities but used without great care can strip the wine of its colour and most of its character. The downside of filtration is that the more solids the filter blocks, the more clogged it becomes. Some wineries now use tangential or cross-flow filtration by which the wine flows over the membrane horizontally instead of through it vertically, and with much better results.
Fining is another, and ancient process, for cleaning wine in which an albuminous protein substance is mixed into the wine and gradually sinks to the bottom taking with it any unwanted particles in suspension. In the past things like ox blood and egg white and later gelatine, casein and isinglass were used, but with the advent of veganism most wineries now use bentonite, a form of clay. Traditionally a dozen or so egg whites were beaten into a foam with a few sprigs of thyme and mixed into a jug of the same wine then poured into the butt and stirred in with a stick. After a few days some fine clay from Lebrija would be added to finish the job before racking the wine into a clean butt. The yolks usually went to a convent where the nuns would use them to make sweetmeats. Fining agents work by having a different electrostatic charge to the substances to be removed attracting them to each other and thus falling out of solution by gravity.
Yeso (or gypsum – calcium sulphate - plaster), while not strictly speaking a fining or filtration agent, certainly helps with stability. It has been used for centuries and was traditionally added during pressing to increase must acidity, help fermentation and the longevity of the wine and reduce the presence of potassium bitartrate while increasing aromas. XIX century English doctors tried, unsuccessfully, to condemn the process of “plastering the must”, and though science has since shown it to be wholly beneficial, it has died out on its own as the grapes used nowadays are very rarely sunned and therefore retain a little more acidity.
Consumers are always on the lookout for “natural” food and drink, but have little idea what “natural” really means. They are used to wines which are often over stabilised so as to be problem (and thus often character) free. So they get a bit of a shock when wine has sediment or is hazy or even has an odd colour. And so we come to the thorny subject of sulphites. Sulphur is one of the most abundant elements on the planet, and while it is impossible to make wine completely free of it, it is possible not to add any more – so long as you really know what you are doing. This natural substance has been added to wine for millennia as a cheap and effective antioxidant which keeps the wine smelling and looking fresh while it also inhibits the fermentative abilities of yeast. It is normally used in the form of sulphur dioxide (SO2) gas and amounts used are strictly regulated by law since a small percentage of the population is allergic to it, which is why its presence must be stated on labels if the (dry white) wine contains 210mg/l or more - and they all do. These days the minimum possible is used and there is constant research into alternatives which is beginning to bear fruit. It seems very unfair, however, that food labels can simply put “E 220” on the label while wine labels must put “contains sulphites” which really worries consumers, for the most part completely unnecessarily.
In the end, as always, it boils down to the type of consumer. There are the connoisseurs who understand that wine is a living thing which will inevitably evolve throughout its entire existence and take great pleasure from that, being prepared for most eventualities. And then there are the less well-informed consumers with very little understanding of wine who see a trace of sediment or a little tartrate crystal in the bottle as catastrophic. After over 40 years in the wine trade I would estimate that hardly any of the bottles which were returned were genuinely faulty. It was nearly always a question of the customer simply not liking the wine or not understanding it. That says a great deal for the stabilisation processes - not to mention the corks which protect the wine.