Best Practices for Juice Clarification via Flotation
Last updated: 6/2021
Applies to: Winemakers looking for product and process recommendations for clarifying/removing solids from white and rosé juices via flotation.
The Importance of Clarification
Juice clarification is an important consideration in the production of white and rosé wines. Freshly pressed must can contain up to 20% solids consisting of small particles of cellulose, hemicellulose, pectin, mineral salts, lipids, and proteins. Based on variety and pressing method, the quality and quantity of grape solids in a juice can vary widely; however, it is beneficial to reduce solids content prior to fermentation for all white and rosé juices to 60-250 NTU’s or 1-2% solids.
NTU's, or Nephelometer Turbidity Units, are a unit returned by a Nephelometer and help quantify the "cloudiness" of a juice or wine. This instrument is not only helpful when clarifying juice, but at many points throughout the winemaking process including heat stability and filtration.
Benefits of solids reduction (clarification) include:
- Fresher, fruitier wines
- Reduced sulfur-like off odors
- Better color as enzymes responsible for oxidation have been removed
- Reduction in vineyard residues (e.g., SO2)
- Reduction in acetic acid producing native microflora
- Compact deposit which minimizes juice loss
- Increased fermentation kinetics
Clarification can be achieved via:
- Static Settling
What is Flotation?
3 STEPS OF FLOTATION
Flotation is an expeditious method of juice clarification that can lead to clarified juice without the need for chilling. During flotation, gas is injected into the bottom of the tank and solids rise to the top of the tank leaving clarified juice below. There are 3 main steps to flotation:
- Add Flotation Aids: Flotation aids are added that cause floccules to form through the agglomeration of juice solids with the added flotation aids.
- Inject Gas: Microbubbles of gas are injected into the bottom of the flotation vessel and form adhesive relationship with the hydrophobic floccules.
- Wait for Cap Formation and Rack: Once this adhesive relationship is formed, the floccules, which have a lower density than juice, float to the top of the tank. Clarified juice can then be racked from the bottom of the tank.
Benefits of flotation include:
- Faster clarification than static settling
- Juice loss is minimized
- Juice does not need to be chilled
- Inoculation can occur faster
Considerations During Flotation
While flotation is a technical process, it can be achieved irrespective of winery size as long as the concepts are understood and key considerations are respected:
CONFIRM JUICE IS PECTIN-FREE
When grapes are pressed, pectin is released into the must. The amount depends on varietal, degree of ripeness, harvest method, skin thickness, and contact time. Pectin will prevent cap formation and keep solids and clarification aids in suspension. Therefore, pectin removal is key to a successful flotation process and can easily be achieved by adding a pectinase (enzyme). Choosing the correct pectinase, dosage, and contact time is essential.
Enzymes & Dosages:
- For difficult to clarify juice add one of the following enzymes directly to the press pan:
- For easy to clarify juice add one of the following enzymes directly to the press pan:
Contact Time: After several hours of enzyme contact, confirm juice is pectin free by conducting a pectin test. If pectin is still present, verify juice is warmer than 55°F and add more enzyme. Retest after several hours. Juice must be pectin free before continuing with flotation.
USE APPROPRIATE FLOTATION AGENTS
Once the juice is confirmed pectin free, flotation agents should be added. Traditional clarification aids used during the flotation process include gelatin, bentonite, and silica gel. Chitosan is an animal and allergen-free alternative derived from fungal cells. To achieve the desired level of clarification, any agent should be trialed to determine dosage.
- Floccing Agents are highly charged products that allow for the formation of strong floccules, improves cohesion, and helps adherence to the gas bubbles.
- Bentonite is used to attract the positively charged compounds in the juice, and aid in juice cap compaction.
- NACALIT® PORE-TEC: 10-30 g/hL
- Silica Gel is a colloidal solution that helps generate larger flocs making clarification more efficient. It should be used in conjunction with COLLE PERLE if bentonite is not used.
- GELOCOLLE: 30-80 ml/hL
CHOOSE THE RIGHT GAS
Gas is an essential component of the flotation process and several options exist:
- Nitrogen is the most efficient gas for flotation. It forms appropriately sized bubbles, has low solubility and minimal side effects.
- Filtered Air is a good, cost effective choice, though care must be taken to avoid oxidation.
- Argon is a good, inert choice like nitrogen but it can be cost prohibitive.
- Carbon Dioxide forms too large of bubbles for flotation which can result in foam and juice handling challenges.
- Oxygen forms appropriately sized bubbles; however, oxygen is very reactive and can cause unwanted side effects like oxidation.
- Use the correct equipment for flotation (flotation unit and tank of appropriate size/shape OR ensure your equipment is compatible)
- Manage temperature (ideally between 60-70°F, and NOT below 55°F)
- Ensure no fermentation has taken place
- Ensure size and shape of tank is conducive for flotation
- Ensure the tank is not too full that a cap cannot form
Addressing Other Fruit Quality Concerns During Flotation
It is possible to conjunctively address fruit quality concerns during flotation. The following products are compatible with the process:
- GRANUCOL® FA is a decolorizing carbon and can be helpful at 10-50 g/hL (must be used with NACALIT® PORE-TEC) to remove unwanted pigments (brown/pink), help target color in rosé, etc…
- POLYCEL is a PVPP product and when used at 40-80 g/hL, it can help remove color or bitterness and can assist addressing press fractions.
- POYLCACEL is a PVPP & casein blend and when used at 30-70 g/hL, it can help remove browning/pinking and address some sensory issues like moldy/musky juices for example.