Levels of Ochratoxin A in vine-based products

A Technical Guide
for Wine Producers

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Preliminary code of sound vitiviniculture practices in order to minimise levels of Ochratoxin A in vine-based products

Preamble
Mycotoxins, in particular Ochratoxin A (OTA), are secondary metabolites produced by filamentous fungus found in soil and organic matter, which spread and thrive on grapes during the berry ripening phase. The formation of OTA in grapes is mainly due to berry contamination by certain mould species belonging essentially to the Aspergillus species (in particular A. carbonarius species and to a lesser extent A. niger). The presence and spread of such fungus in vineyards is influenced by environmental and climatic factors, nocturnal dampening condition of grapes, the shape of the grape bunch, susceptibility of vine varieties, aeration level of grape bunch zone, health status of grapes and berry injuries which are the main entry points for ochratoxinogenic fungi.
Cultivation practices in the vineyards
All recommendations in the OIV document on sustainable vitiviniculture guidelines need to be respected, in particular the aspects concerning the establishment of vineyards, soil management, irrigation, and cultivation practices in the vineyards, pest control and the harvesting process.
The OIV recommends applying the following preventive measures in viticultural regions in which the climatic conditions are favourable for the formation of OTA in vine products in order to reduce epidemic risk which favours the onset of very damaging vine diseases:
Training of producers

Ensure training of producers with regard to:

Risk of mould and mycotoxins,
The identification of ochratoxinogenic fungi and period of infection,
Knowledge of preventive measures to be applied to vineyards and in wineries.

Establishment of vineyards

Establish vineyards in a well ventilated area with low humidity.
Soil potential, row direction, prevailing wind directions, rootstock and scion characteristics, trellising system design and economic factors should be considered in the layout of the vineyard to:

Facilitate planting operations,
Position grape bunches correctly above the soil,
Ensure good pest and disease control,
Promote the uniform ripening of the grapes.

Plant material

Choose varieties which are less prone to develop mould and berry rot and with less rootstock vigour.
Choose clones or biotypes within a variety which are better adapted to climatic and soil conditions in the specific cultivation area and which are often characterised by less compact grape bunches.
Lay out homogeneous plots of land (varieties, clones) to facilitate growing operations and to ensure better crop and disease control and to obtain uniform ripening of the grapes.
Growing techniques

Apply management practices which favour leaf/fruit balance for vines and which reduce excess vigour, in particular, to minimise nitrogenous fertilizer applications.
Favour cover crop and soil covering and avoid working the soil between the beginning of the grape ripening and harvesting period in order to prevent dirt particles on the grapes.
Space grape bunches such that overcrowding is minimized.
If water input is necessary, irrigate as regularly as possible in order to avoid berry bursting and the onset of cracks on the skin which are sources of mould penetration and development, especially in warm regions.
Avoid using marc containing ochratoxinogenic fungus as a fertilizer in the vineyards.
Pest and Disease control

Remove leaves in the grape cluster zone taking into account the risk of sun burn. This will facilitate the aeration of clusters (which is particularly necessary under hot and humid weather conditions) while the grapes are ripening.
Avoid lesions on the berries and skin damage caused by diseases, insects, phytotoxicity and sun burn.
Apply registered fungicides in order to control important grapevine diseases affecting grape quality (o‹dium, botrytis, sour rot, etc.).
Prevent attacks of grape berry moths, grape mealybugs and grape leafhoppers which favour mould development on damaged berries. Pest control needs to be carried out according to biological and epidemic risk. Under high risk conditions preventive treatments must be applied by using specific products and taking into account the warnings of plant protection regional services.
Apply appropriate protective programmes against grape rot and mould. Specific treatments are recommended in all situations which are favourable to the development of toxin producing species (A. carbonarius, A. niger).
Practices at harvest

"The OIV Resolution CST 1/2002 sets maximum contents of Ochratoxin A (OTA) at 2,0 mg/l for wine. The objective is to maintain product safety and consequently protect the health of consumers. "Given the importance of this issue growers and winemakers are encouraged to familiarise themselves with the Preliminary Code of sound vitivinicultural practices in order to minimise levels of OTA in vine-based products." Jan Booysen, Executive Manager, Winetech

A healthy grape harvest can ensure optimal quality and safety of vitiviniculture products. Consequently, only a healthy grape harvest can be used for human consumption without the risk of quality loss and without food safety problems for consumers.
The date of harvest must be decided taking into account grape ripeness, sanitary level, and forecasted climatic changes and epidemic risk. In high risk OTA areas, it is recommended to advance the harvest date.
When grapes are extensively contaminated by mould:

The grapes cannot be used for human consumption, neither fresh or in raisins, nor for making concentrated musts, wine, grape juice or vinegar.
The grapes can only be used for distillation.
Production of raisins and raisined raisins
For production used to obtain raisins and raisined raisins (sweet wine) the OIV recommends that the following should be observed:

Ensure the hygiene of containers to be used for the harvest and/or the drying of grapes.
Use only grapes not damaged by insects and not contaminated by mould.
Sort grapes by eliminating damaged or contaminated grapes.
Place grapes to be dried or raisined in just one layer to avoid overstacking.
Favour progressive and uniform drying of all parts of the grape bunch.
Take the necessary measures to avoid development of drosophila's.
For particular conditions of drying in open air, it is recommended to dry in well ventilated conditions and to cover the grapes at night to prevent condensation and humidity.
Production of wine grapes
The OIV recommends the following actions in the case of a harvest that is moderately contaminated with ochratoxinogenic mould and is to be used in wine production:

Grapes damaged by insects, mould, or contaminated by dirt particles must be eliminated at harvest time.
Grapes need to be sorted (e.g. hand-picked harvests), in order to separate the grape bunches or the damaged parts of the bunches. It is important to discard grapes with black mould.
Harvested grapes must be transported as quickly as possible to the winery in order to avoid extended waiting, especially for grapes with a high proportion of juice.
It is important to clean containers after each load, especially in the case of rotten harvests.
Practices at the winery
Under high-risk OTA contamination conditions, it is recommended to measure the contents of OTA in the musts to be used in winemaking.
Operations and pre-fermentation treatments

In the case of mechanized harvests, appropriate sulphiting and/or prevention techniques should be carried out in order to prevent rapid and uncontrolled fermentation.
In the case of contamination, use higher doses of sulphur dioxide.
Avoid skin maceration in the case of OTA high-risk harvests or carry out maceration over a short period of time.
In the case of a significant contamination of red grapes, consider the possibility of the making of ros‚ wine.
Adapt the pressing rate to the health status of the grapes; in case of contamination, carry out small volume, low-pressure, quick pressings. Avoid continuous pressing.
In the case of contaminated grapes, avoid using pectolytic enzymes for racking must or maceration. Quick clarifications with must filtration, centrifugation and flotation are preferable.
Avoid berry/must heating treatments and aggressive and prolonged macerations.
In the case of contamination of white musts, it is advisable to treat with a low dose of oenological charcoal in accordance with prevailing legislation in order to avoid higher dose treatment afterwards.
Fermentation treatments

Fermentation and maturation should be done in smooth-walled containers to avoid sources of contamination linked to previous fermentations or maturations and also to facilitate cleaning.
For alcoholic or malolactic fermentations, use yeasts or bacteria which have absorbent properties for OTA; ensure that these characteristics are guaranteed by the supplier. Note that the usage of these products only enables a partial reduction of OTA.
It is recommended to rack as quickly as possible after fermentation.
Maturation and clarification treatments

Active Dried Yeasts, yeast cell walls or inactive yeasts can help reduce the level of OTA.
Maturation on lees can help reduce the rate of OTA formation. The risks of this technique related to the organoleptic quality of the wine should be evaluated.
Current clarification products (organic or inorganic fining agents) have variable levels of efficiency for reducing contents of OTA as:

Cellulose has a relatively small effect,
Silica gel associated with fining with gelatine enables a significant reduction,
Oenological charcoal authorised exclusively for white winemaking is the most efficient.

Acquaint oneself with efficiency of the product used and application techniques.
Carry out trials with different dosages to determine application rates and to avoid sensory problems.
Conclusion
These recommendations are based on current knowledge and can be updated according to research to be pursued. Preventive measures are essentially carried out in vineyards and treatments in the wineries are purely corrective measures.
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