What are the differences between cleaning, sanitation and sterilisation?
Cleaning is the removal of visible dirt, debris or unwanted material (solid or liquid) from a surface. This can include removing grape solids from the winery floor using a broom or removing colour or tartrate deposits from tanks after fermentation. Cleaning needs to be done before any sanitation steps, to ensure that sanitisers make contact with the surface that needs to be sanitised. Typical cleaning agents include water (hot and cold), sodium or potassium hydroxide (caustics), carbonates or percarbonates, metasilicates, citric acid, and physical cleaning actions such as scrubbing, brushing or high-pressure spraying. There are also a range of proprietary blends which may include surfactants (detergents or wetting agents to lift dirt from surfaces) and sequestrants (metal chelating agents), which are important when using hard water.
Sanitation is the reduction of the microorganism load on a surface to a level that minimises microbial spoilage potential. Wineries define sanitation as a 3 log or 99.9% decrease in cell number. Typical winery sanitisers used in Australia include hydrogen peroxide and peroxyacetic acid (peracetic), sulfur dioxide, alcohol solutions, hot water and/or steam. Detergents and surface spray cleaning agents are typically made of a range of chlorine-based agents, often with added artificial flavours (citrus/lavender). These can be used in office and laboratory spaces but should be avoided on winery tanks, floors, barrels and packaging lines to prevent chlorophenol, chloroanisole and artificial flavour taints. Specific information is also available on winery sanitation and COVID-19.
Sterilisation is the complete removal or inactivation of all living microorganisms present. Sterilisation is achieved by maintaining high temperatures for a fixed period of time (dry heat or flaming, heating under pressure and/or hot water or steam), by physical removal of microorganisms through absolute membrane filtration, or using chemical treatments such as dimethyl dicarbonate to inactivate or kill all living organisms. Verification testing is required after sterilisation to determine if the treatment has been successful.
What needs to be cleaned, sanitised or sterilised in a winery?
Floors, walls, ceilings, drains, fermenters, tanks, barrels, hoses, hoppers, crushers, presses, fittings and fixtures, buckets, plungers, sampling devices and anything that makes contact with wine should be cleaned before and/or after use. Sanitation is typically performed before use. Sterilisation steps are generally reserved for bottling operations.
Cleaning during vintage
Crushers, presses and must lines should be cleaned and sanitised regularly (at least daily) so that populations of unwanted microorganisms can be kept to a minimum. Keeping processing equipment clean will also help prevent the accumulation of organic material, which can provide a food source for microorganisms.
Floors walls and ceilings
Floors and walls of cellar areas should be rigorously cleaned at least twice per year, to remove ingrained dirt, colour material and biofilms that will inhibit the effectiveness of daily cleaning operations. It makes sense to do this once before vintage commences and again once vintage is complete. This also applies to crushers, hoppers, some presses, pumps and winery grape bins. Any full tanks of wine should be sealed or moved before any cleaning commences in the area.
Floors can be washed and scrubbed (with scrubbing brushes/brooms) using cold then hot water or using cold water with a high-pressure cleaner. High-pressure cleaning nozzles can aid in cleaning floors and winery machinery. Use on walls will depend on their composition. Water used for cleaning should ideally be potable water to prevent scale residue. Non-potable water can be used for daily cleaning of floors to wash away grape and wine sediment. To conserve water, a variety of stiff brooms, rubber brooms and squeegees are available to direct solid wastes to drains/sewer traps. Preventing gross solids from entering the winery drainage systems will also reduce the chance of off-odours building up in the waste lines. Gross solids can be collected with grape marc.
The internal surfaces of winery stainless steel tanks generally require cleaning after fermentation, settling, fining and stabilisation cellar operations. Both fermentation and cold stabilisation will result in a significant ‘tartrate’ coating of the tank walls, as well as red pigment staining from red wines. Vertical stainless-steel tanks are often cleaned with caustic or other basic solutions, citric acid, peroxides and hot water. The process can be aided with manual scrubbing for small tanks or with spray balls or rotary cleaning spray heads. Appropriate safety clothing and glasses/goggles should be worn during these cleaning operations.
When cleaning tanks, it is recommended to remove all rubber o-rings from doors or fittings and clean these by hand. Sample valves, taps and gauges should also be opened and closed during the operations to ensure the cleaning solution makes contact with all tank surfaces. Black moulds on the outside surface of tanks can only be removed by regular manual scrubbing.
Cleaning tanks with a spray head
Tanks should be first rinsed with water to remove bulk solid waste. Tanks should be filled with water to approximately one twentieth the size of the tank (e.g. 500 L for a 10,000 L tank), or so that there is sufficient water to fill the base of the tank and fill liquid through the pump. Water is pumped from the bottom racking valve and returned to the top of the tank via the spray head. The tank door should be shut, or only slightly ajar during these operations. Washing is then repeated with a caustic agent. Preparation (concentration and temperature) will depend on the product used. A caustic solution is usually prepared outside the tank to ensure thorough preparation/concentration. The caustic is circulated through the spray head for approximately 20 minutes or until colour and tartrate have been visually removed. If the tank is still unclean, more caustic should be added and the process should be repeated. A citric acid solution (0.6%-1%) should be circulated for five minutes to neutralise the caustic, the tank should then be rinsed with water and allowed to drain. Any o-rings and fittings previously removed should then be replaced and allowed to dry.
Cleaning tanks by hand
Cleaning tanks by hand generally requires workers to enter the vessel and use scrubbing brushes and the same cleaning agents described above or high pressure spray guns using warm water. Requirements for confined space entry, safety clothing, equipment and procedures must be followed in these cases.
Cleaning hoses and fittings
Hoses are cleaned after use by first flushing with water to remove any residual wine. Hoses can be cleaned while cleaning a tank, using a pump with two hoses to move the caustic or citric liquid from the bottom of the tank to the top spray ball. Hoses can also be cleaned separately. One hose is connected to a pump inlet and one to an outlet. Both hose ends are then placed in a 200 L tub filled with a 0.5-1.0% caustic solution and the liquid is circulated for five minutes. The caustic is then emptied from the lines and the inlet placed in an equivalent tub of 5% citric acid. A tub of caustic and citric can be placed on a pallet or mobile unit that can be moved to where cleaning needs to take place. Solutions should be remade once they become discoloured or diluted. The lines are then rinsed with water. Cleaned hoses should ideally be placed off the ground to hand dry rather than coiled and left on the ground. This way hoses can be used immediately when needed rather than needing to be cleaned again before use. Similarly, cleaned fittings can be placed on a designated equipment rack to aid in finding equipment easily and to know the materials have been cleaned.