Friday, May 20, 2011

O.T.R. not O.T.T.

Angela measures oxygen in the head space

The care and attention that we take in making the best wine that we can does not stop at the cellar door when pallets are shipped out to our customers, we obviously try to guarantee (as far as we can) that our customers will enjoy our albari├▒o once they pull the cork.

You may have heard me comment on previous occasions that one of the biggest enemies of the winemaker (and possibly more especially white wine makers) is that of oxidation. Now, oxidation can and does occur at every stage of the wine making process, and so we make it our goal in life to ensure that it is kept to the absolute minimum, thereby ensuring the freshest possible wine that we can.

Fruit oxidation starts from the first moment that the skin of the grape is broken, and quite obviously is exacerbated every time the grape must or finished wine is exposed to the air. It is also made worse by the use of pumps that serve to agitate the wine as they force our precious liquid through the pipework. In the case of Castro Martin the need for pumping is largely offset by the very design of the building itself. Our vinification takes place over three different levels and we can therefore simply move our wine around by gravity.

Once the wine is actually made there are three further opportunities for oxidation to take place. The first is during the tank storage period, which is why we ensure that our wine is kept under a 'blanket' of nitrogen, and also explains why we store in tank, and only bottle as and when floor stock is required.

The second is at the time of bottling, where we do our very best to ensure that all possible oxygen is removed from the empty bottle and that nitrogen is added once again, a split second before the cork is put in. The small gap in your bottle between the cork and liquid (known as the head space) can perhaps unbelieveably account for up to 80% of the total oxygen contained within the bottle - the rest being present in the wine itself.

The third opportunity for oxidation is after bottling, when the cork finally seals the package. Over the years we have spent a lot of time studying this, and run many tests on different types of wine closure. The best and most expensive natural corks are of course very good, but will always be subject to a small percentage of spoilage caused by TCA (cork taint). The secret therefore is to find something that behaves like a cork, but does not allow a wine to become tainted. Our own solution is Nomacorc, a synthetic closure that provides a very good (and consistent) seal, whilst at the same time allowing an almost microscopic transfer of oxygen, measured by OTR - the oxygen transfer rate. Believe it or not a closure that provides a completely hermetic seal can also cause problems. The sulphur that is added to protect wine needs to escape slowly over time, and if it becomes trapped it will eventually be absorbed back into the wine. This can actually cause a different type of 'off' flavour (sometimes similar to burnt rubber).

Oxygen readings taken in tank

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