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winemaking juice following transfer or manipulation. New technology using fluorescent materials may provide rapid enough analysis to observe oxygen in must. In the case of oxidation of white wines and juices, the appearance of brown pigment can be used as an indication of the level of oxygen pick-up by the wine, and of its fate. In red juices, loss of color can be monitored, and in wines the appearance of aldehydes is correlated with oxygen level. Other factors in red and white wine influence oxygen uptake, penetration and impact including the temperature at which the wine or juice is stored; at lower temperatures, the amount of oxygen necessary to saturate wine or juice increases.16 Impact of aeration treatments during fermentation In addition to PPO activity, the micro organisms present in juice also consume oxygen. Many organisms present on the surface of grapes, particularly the bacteria and molds, are obligate aerobes. These organisms can compete with PPO for the oxygen present in juice. It appears, however, from the rapid production of quinones under these conditions, that PPO activity, if uninhibited by SO 2, consumes more oxygen than microbial activity early in juice.29 As microbial populations build, or if the juice contains a high bio-load, there may be more microbial competition with PPO than would occur normally. Grape surfaces also contain fermentative organisms, Saccharomyces and nonS a c c h a ro m y c e s y e a s t s . A l t h o u g h fermentative, these organisms will also consume oxygen to synthesize cellular components required for growth and to aid in the transition from respiration to fermentation as the mode of energy generation. As these populations grow, they compete with PPO for oxygen in juice.4 Thus the fate of oxygen in juice is dependent upon the relative ratios and activity of the microbes present and PPO activity. A third factor affecting the balance of PPO versus microbial consumption of oxygen is the presence of SO2. It influences the rate of O2 consumption, with the rate declining dramatically with SO2 addition due to PPO inhibition,16 leaving oxygen-available microbes. However, SO2 is also toxic to microbes, especially bacteria and some wild yeast such as Hanseniaspora, so its use can also reduce microbial demand on the oxygen supply. Saccharomyces is resistant to SO2 and is able to detoxify this compound and grow in its presence. Saccharomyces, once established, outcompetes PPO for dissolved molecular oxygen. In addition, the ethanol of fermentation inhibits PPO activity. There are several factors impacting how long oxygen remains in the juice environment during fermentation. CO2 production during fermentation can also cause oxygen to be sparged out of the wine, because the large volume of CO2 being created during fermentation absorbs oxygen and sweeps it out of the fermentation as it forms gaseous bubbles.5 Addition of diammonium phosphate (DAP) can greatly impact fermentation behavior.22 Use of DAP is to avoid fermentation issues such as sluggishness or sticking by providing extra nitrogen, utilizable by yeast. Nitrogen supplementation to increase fermentation rate and CO2 production can lead to a more rapid O2 depletion, due to volatilization, blanketing and consumption in the presence of a more active biomass. During fermentation, oxygen availability allows a more rapid development of COMPLETE CRUSHPAD SYSTEMS LT™ & LT 2+2™ MOG Separators Fruit Receiving Systems Bin Dumpers Sorting Tables Belt Conveyors Screw Conveyors Vibratory Conveyors Presses Destemmers & Peristaltic Pumps Destemmers, Mohno Pumps & Crush Rollers USED BY THE FINEST WINERIES TO ACHIEVE THE BEST RESULTS Call Now to Schedule Design Appointments! 1650 Almar Parkway Santa Rosa, California 95403 P 707 573 3141 • F 707 573 3140 www.pnlspecialties.com CA Contractor's #803431, OR Contractor's #180330 WA Contractor's #PLSPELS923BZ S O L U T I O N S • E X P E R T I S E • Q U A L I T Y • S AT I S F A C T I O N pr actica l win ery & vin eya r d O CTO B ER 20 13 73