Wednesday, 20 January 2016

What are Enzymatic Biosensors?

These are incredibly useful gadgets which can measure the health of the grapes at the point of reception at the bodega. A common problem at harvest time is Botrytis (Greek = grape disease). This fungus can spread quickly in wet or humid conditions and produces unsightly grey mould on the grapes which can cause various problems during fermentation.

Botrytis affected grapes: no good for Sherry
A key marker for Botrytis is an increased level of gluconic acid (GA) caused by oxidation of the glucose metabolism, and a concentration of over 0.5 g/l of GA can put the must at risk. Biosensors can measure levels of not only glucose (in degrees Beaumé) but also GA - in seconds. The biosensors can also measure malic acid, lactic acid, histamine and sucrose in the must. Selected enzymes react to other substances and a transducer converts this to an electrical signal. In 2011 the Consejo Regulador imposed a limit of 1 g/l of GA in the regulations as it was becoming a problem due to less care in the vineyards as growers struggled with profitability, and the advent of harvesting machines which cannot detect Botrytis - yet. Deductions can be made from the sensors’ results, for instance a grower might not have used sufficient fungicide spray.

Developed by Spanish company Biolán, the biosensors are not cheap, costing 6,000 euros plus the cost of someone to operate them, but eventually pay for themselves with higher quality musts. The arriving grapes must pass a sensor which will spot GA and pass the information to measuring devices. On detection of excess GA unsuitable grapes can be removed. In the past the only way of checking for Botrytis was complex and time consuming laboratory work or an equally time consuming visual inspection.

Biolan Biosensor monitor
It should briefly be pointed out that Botrytis is used to advantage for certain other wines. The great sweet wines of Sauternes, Côteaux du Layon or Sélection de Grains Nobles in France, the Beerenauslesen and Trockenbeerenauslesen of Germany and Tokaji Aszú from Hungary are at their best with a healthy dose, but not if you want dry wine.

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