Wine Analysis Home

Bumping

• Bumping is the sudden mass release, sometimes violent release, of water vapour from liquids being heated.
  
  
• When a liquid is heated to its boiling point (100 ^oC @ 1 atm), with time, all of the liquid will gain enough energy to vapourise in to steam.
  
  
• Water vapour or steam is easily liberated from the water's surface, however, within the body of the liquid, the water vapour is released through the formation of water vapour bubbles that rise to the top, producing the turbulence we recognize as boiling.
  
  
• These vapour bubbles are formed from seed bubbles, which enlarge as more vapour is incorporated, until they gain enough buoyancy to rise to the surface of the liquid and released as water vapour or steam.
  
  
• These seed bubbles are formed within the liquid on a microscopic level.
  
  
• The formation of these seed bubbles require nucleating points or starting points.
  
  
• Nucleating points can consist of small surface irregularities of the container, impurities or solids within the liquid having surface irregularities.
  
  Sometimes bubbles contained within these solids, if they are of a porous nature, can also act as nucleating points.
  
  Even bubbles formed from the dissolution of dissolved gasses, within the liquid being boiled, can also act as a nucleating source.
  
  
• Few nucleation points are present in the distillation of wine for alcohol determination or steam generation for VA determination for the following reasons -
  
  
  • Most of the dissolved gases contained within the wine will be removed at the early stages of the boiling process and hence no longer serve as a source of nucleation for the remainder of the process.
    
    
  • The liquid being boiled is usually contained within a smooth glass boiling flask with few surface irregularities, especially if it is a new flask.
    
    
  • The wine has usually been settled and removed from impurities.
    
    
• These conditions make it difficult for water vapour bubbles to form, creating pockets of highly energized, superheated water, that, when it finally forms vapour bubbles, the bubbles can be large, abrupt and violent, releasing the accumulated energy in one violent discharge.
  
  
• To prevent this from occurring, anti-bumping granules are added to the liquid, to allow a continues, even formation and release of vapour bubbles and energy, giving rise to a smooth boiling action
  
  NOTE: Do not add the boiling chips to wine that is being heated as this can result in a possible violent release of energy.
  
  Allow the wine to cool down and then add the boiling chips, connect the flask and resume heating.
  
  
• The anti-bumping granules can consist of small glass chips, porous ceramic chips being both irregular and containing small bubbles of air within their structure, as do boiling sticks. Pumice powder or chalk dust can also be used.
  
  
• It is interesting to note that there have been cases reported where water that has been heated in a microwave, in a smooth coffee cup (glass or ceramic) to make a cup of coffee, has instantly exploded on removal or when disturbed when introducing an object such as a spoon.
  
  This occurs, as these conditions produce superheated water (>100^oC) and release the energy in one violent motion when bubble formation is finally triggered.
  
  A less violent version of this phenomenon can be observed as the bubbling or frothing that occurs when adding coffee or a tea bag to water heated in a microwave.