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Fermentation is the process of converting grape juice into wine with the addition of yeast. Selected wine yeasts may be added to the must by the winemaker, after which fermentation may take up to 10+ days to complete, depending on the grapes, the temperature of the must, and/or the wine style desired. Fermentation converts the sugars in grape juice into ethanol, with carbon dioxide and heat also being produced in the process. Fermentation is generally considered 'complete' when all of the sugars have been converted into ethanol. Fermentation is commonly carried out in tanks, Macro Bins, or barrels.

Possible Hazards:

Release of Carbon Dioxide (CO2) into Work Areas

    Fermentation produces carbon dioxide gas about 40 times the volume of grape juice. Excessive carbon dioxide in the air can cause headache, sweating, rapid breathing, increased heartbeat, shortness of breath, and dizziness. The number and severity of symptoms may vary between individuals. Higher levels of carbon dioxide can result in more serious and immediate effects including coma, asphyxia, convulsions, unconsciousness, and death.

    Carbon dioxide has several occupational exposure limits set to help prevent harmful exposure. Along with air tests and exposure monitoring, the limits may be used to identify needed controls or determine the effectiveness of existing controls. The State of Washington exposure limits for carbon dioxide are 5000 ppm as averaged over an eight hour work shift (TWA8) and 30,000 ppm as a short term exposure limit averaged over any 15 minute work period (STEL15). The immediately dangerous to life and health (IDLH) value as recommended by the National Institute for Occupational Safety and Health (NIOSH) is 40,000 ppm (4%). This value was established for the proper selection of respiratory protection equipment and to prevent a worker from being unable to self-escape or suffering irreversible harm after 30 minutes of exposure at the IDLH level. Exposure to 70,000 ppm (7%) would be more immediately dangerous in that unconsciousness can occur within a few minutes. Regulatory agencies may use the 40,000 ppm value as a maximum limit for any unprotected exposure.

    The venting of carbon dioxide from tanks or open top fermentation bins can result in the spread of the gas into all work areas to which it is able to diffuse or travel. Whether a hazardous buildup occurs is dependent on the amount of grapes fermenting, room size, and natural and mechanical ventilation available in the rooms and building. Pumping over wine or "punching" the cap (skins, seeds, stems, and pulp that have floated to the top) can release additional carbon dioxide in the immediate area as well as contribute to the buildup. Workers whose tasks require them to be over open bins or tanks undergoing fermentation can expect a higher exposure. Tanks or even open top Macro Bins partially full of fermenting grapes can have headspaces with toxic carbon dioxide levels and oxygen deficiency. Additionally those who work at night with the building closed up or who open the next morning may be exposed to even greater levels of carbon dioxide. A poorly ventilated room or building can have carbon dioxide levels build up to exceed 40,000 ppm (4%), the NIOSH immediately dangerous to life and health (IDLH) value.

    About CO2 and O2 Meters
    A meter that measures air levels of carbon dioxide (CO2) and oxygen (O2) is a necessary tool for any winery. A CO2 meter may be used to check the progress of fermentation and an O2 meter to verify the proper atmosphere when inerting tank headspaces with argon or nitrogen. Importantly, CO2 levels also need to be checked to verify safe levels for worker tasks during fermentation and both CO2 and O2 checked prior to confined space entry.

    These meters are available from both beverage industry and safety equipment suppliers. Most of the available CO2 meters have a range up to 5000 or 10,000 ppm. If you declare your "action level" at a value below this upper range, then one of these meters may be suitable. However, it is recommended that a CO2 meter be obtained with a higher range. Manufacturers of the later type include Bacharach, Chart Industries, CO2 Meter, PCE Instruments, and RAE Systems. A couple of manufacturers combine the carbon dioxide and oxygen sensors into one portable meter. Maintenance and calibration are necessary for reliable use.
    • Provide adequate mechanical exhaust ventilation and fresh air supply during times of fermentation for tank rooms, barrel rooms, cellars, and other areas that may accumulate carbon dioxide. During the time needed to add any mechanical ventilation, use natural ventilation by opening the building without entry (roll up doors used to ventilate may need to be changed to open from the outside). After there has been sufficient time for natural ventilation to lower the carbon dioxide to safe levels based on test data, entry may then be made.
    • Test the levels of carbon dioxide in work areas and for workers performing tasks with potential exposure and compare with the occupational exposure limits. This will provide an assessment of the effectiveness of work practices and ventilation and alert to the need for further control. Those who conduct air tests need to consider their own safety and may use remote means of testing. Professional assistance is available see Resources.
    • Fatality in 2014 at Spanish Winery
      A wine worker was punching a large full wine tank undergoing fermentation when she was apparently overcome by carbon dioxide. Her fall into the tank resulted in her death.
    • Provide chemical hazard communication to employees on carbon dioxide and safe work practices for tasks and work in fermentation areas. Workers need to know the signs and symptoms of carbon dioxide toxicity and oxygen deficiency so that they may take any necessary protective steps and alert others.
    • Pump over sprinkler systems can be engineered into the tank itself, reducing the need for workers to stand over fermenting tanks.
    • Prohibit workers from placing their heads into the headspaces of open tanks or open top Macro Bins partially full with fermenting grapes. Samples may be taken with a vial and extended handle or a barrel thief.

Fall from heights

    Adding ingredients to wine tanks during fermentation, inspecting wine for proper fermentation, or performing pump overs or cap punching requires employees to access the top of wine tanks and bins which can create a fall hazard and risk of serious injury.

    • Access the top of wine tanks or Macro Bins by use of fixed work platforms, rolling staircases, or mobile platforms with guardrails, or if the task allows safe use, the correct type ladder. Ladders must be in good repair and secured when used. Ensure employees are trained on proper set up and use of ladders and mobile steps or platforms .
    • Make sure guardrails are affixed to open-sided work platforms or floors 4 feet or more above adjacent floors, and to work platforms or floors above or adjacent to open tanks or vats or dangerous equipment.
    • Engineer tank access, such as cat walks with guard rails around wine tanks when designing new wineries or when remodeling existing wineries.
    • Place tank openings close to the edge rather than in the center on top of the tank, if possible.
    • Implement a personal fall protection system and program when other fall prevention systems are not feasible for fall hazards of four feet or more.


    Placing pump over devices and hoses can be hazardous due to the weight and awkwardness of handling the devices and hoses, which can lead to musculoskeletal stress and crushing injuries of the hands, arms, and legs.

    • Consider having 2 people move and attach pump over devices.
    • Ensure that all temporary crush employees are trained by experienced winery personnel in the placement of pump over devices (POD's), hose attachment, proper attachment of tri-clover clamps and gaskets.
    • If feasible, switch to the lighter weight 'TOAD' pump over device.
    • When doing a pump over by hand (using a reducer valve at the end of a hose), to reduce fatigue it is recommended to rotate workers every 20 minutes.

Dust and Fermentation Nutrients

    Addition of fermentation nutrients/barrel adjuncts (dust hazard). During the fermentation process winemakers may add yeast nutritional supplements and oak dust or chips to fermenting grapes. Both of these substances may contain a substantial amount of dust.

    • Train employees on possible health hazards related to fermentation nutrients.
    • Read MSDS sheets and use appropriate PPE for respiratory protection. Respiratory protection may not be required per MSDS sheet but employees may voluntarily choose to use it when handling these materials.