Several guidelines have to be followed to ensure that additives and processing aids are correctly added to grapes, juice, fermenting must and wine, in order for these products to work optimally. This includes additions like sulphur water (sulphur dioxide), acid, yeast, bentonite and tannins. Incorrect application can result in wasting time and money, and also negatively influence the quality of wine. A few important guidelines for additions in the cellar will therefore be discussed in this article.
Storage and general condition
- Products must be stored in optimal conditions, as specified by the product supplier.
- Ensure that the product is still within its expiry date before use.
- Powders must be dry and the vacuum of yeast packets should be intact. A product like sulphur water should not contain crystals that have formed on the bottom of the container.
- If the product has a suspicious smell when you open it, first find out whether it is the normal smell of the product (e.g. isinglass), or an indication of possible spoilage.
- Maintain a high standard of hygiene in the handling and storage of additives to avoid contamination of the products.
Equipment and hygiene
Additions usually require the use of some form of equipment to execute the action correctly. This may include items like a scale, bucket, measuring spoons, measuring cylinders, measuring bins or vats, a proper whisk (not just a broom handle), pumps and pipes. Even a ladder might be required occasionally to ensure the tank is open at the top before initiating certain actions. These pieces of equipment must be intact, clean and calibrated, and also 100% suitable for the intended action to be performed.
Protective equipment
This aspect is extremely important. Ensure that the correct personal protective equipment (PPE) is used for the task on hand. Rather be too cautious than not careful enough. Accidents can happen very quickly.
Preparation process
The following factors play an important role in this regard:
- The medium in which the processing aid must dissolve, namely water or wine.
- The recommended temperature. Certain types of gelatin, tannins and bentonite dissolve better in lukewarm water.
- Swelling time. Certain additives require a specific amount of time to swell before they can be added, for example bentonite. There are also products that conversely have to be added as soon as possible after preparation, for example powder enzymes.
- The ratio for mixing additives, for example 1 to 10 or even 1 to 20.
Care must always be taken to ensure that there are no lumps in the solution/mixture, and that the additive is homogeneously spread within the water or wine.
Method of addition
The way the additive is added is very important. Simply pouring a full bucket of sulphur water in only one corner of a five-ton load of grapes is not optimal. Rather use a watering can to evenly distribute the additive over all the grapes in the receiving bin.
The most optimal way to add additives to a tank, is to slowly draw the prepared additive into the tank using a pump and venturi. The longer this process takes, the more homogeneously the product will be spread over the entire tank, and the better its efficiency will be. Draw out from the bottom and spread over the top.
An example of a venturi system used to gradually add bentonite to a tank. (Photo: De Krans.)
Sequence of additions
- On grapes in receiving bins: Add sulphur water on the grapes as quickly as possible to protect the juice against oxidation and microbial spoilage. After this the skin-contact or settling/flotation enzymes can be added, but not on the same grapes that came into direct contact with the sulphur water. The best practice is to wait for a short while until these grapes have been carried away by the screw conveyor. Acid additions can then be performed. It is sometimes advisable to perform an acid addition after cold settling right before fermentation, as a more accurate titratable acidity concentration is available at this point.
- On juice: Yeast rehydration is a relatively critical step in wine preparation, because yeast is a living organism and must be kept alive over the course of fermentation in order to ferment dry. It is very important to follow the protocol exactly. The same applies for the preparation and addition of malolactic bacteria. Tannins, yeast nutrients, PVPP and bentonite can also be added during fermentation. These products do not usually impact the action of each other.
- If more than one type of substance has to be added on the same day, it is advisable to start with chemical adjustments like sulphur and acid. Thereafter fining agents like bentonite and PVPP can be added.
- On wine: It is important that all acid adjustments on the final white wine blend are made and that the wine is protein stable (bentonite treatment) before additives like CMC or KPA are added just before bottling.
Mixing
The ideal is that the tank should be fitted with a mixer. Ensure that the mixer works properly and that the wine moves and mixes. If there is not a mixer on the tank, a mixing pump can be used. The acceptable industry norm is that approximately 50% of the tank must be overturned. In effect: a 20 000 L tank, with a 20 000 L per hour pump, should mix for approximately 30 minutes.
The temperature of the wine itself also plays a significant role. The colder the wine, the more difficult it is for most substances to dissolve and in such instances longer mixing will be required.
Many other factors, like the size and form of the tank, the size, speed and even the orientation of the mixer inside the tank, will also determine how long the tank should be mixed. Most cellars establish a standard protocol relatively quickly for how long their tanks should be mixed, given their unique conditions. It is important to ensure that everyone adheres to the protocol.
Follow-up actions
- The process does not stop when the mixer is turned off or the pump is stopped. It is important to make sure the tank is closed properly at the top before leaving the equipment.
- All additives have a specific desired outcome. The outcome is always tied to taking a sample after the addition has been performed and the additive has completed its active period. The sampling tap must be rinsed very well before taking the final sample for the laboratory, or tasting by the winemaking team.
- The minimum or maximum time that should be waited before sampling, is usually indicated by the suppliers on the packaging or specification sheet of a product.
- Some of the most difficult additions to perform 100% accurately, are usually sweetenings like sugar on sparkling wine or grape concentrate. A good practice is to take two samples for analysis – one from the bottom and the other from the top of the tank. This is the easiest way to determine the success of the addition.
Removal
The sediment of tanks treated with processing aids, must be removed using environmentally-friendly methods.
Conclusion
All additions during wine preparation should be fully documented. This is important for labelling and traceability. All documentation of the different additives, indicating compliance of the products to international and South African standards and legislation, should be stored for audit purposes.
If you have any questions regarding the use of additives, contact the suppliers.
For more information, contact Pieter Badenhorst at pieterb@fortheloveofwine.co.za.
Click here to get your copy of WineLand Magazine.
