Wort Aerator....

In general, it is difficult for homebrewers to achieve sufficient oxygen levels. The levels of oxygen necessary for optimal fermentation vary depending on the yeast strain. Ale strains usually need between 8-12 part per million (ppm) while lager strains require slightly higher amounts (10-15 ppm). At atmospheric pressure the maximum level of dissolved oxygen in wort is approximately 8 ppm and the saturation level decreases further as the gravity of the wort increases. Thus unless special steps are taken to introduce air or oxygen into the wort, it is difficult for homebrewers to achieve adequate aeration. Recent studies have shown that oxygenation is by far more efficient than aeration. Injection of oxygen through a 2 micron diffusing stone can actually supersaturate the wort with 10-12 ppm of dissolved oxygen being reached in 5 gallons of wort by a single 60 second blast of oxygen!

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Most homebrewers start out pitching a Wyeast packet. How much are you actually underpitching with one of these 50 ml pouches? Assuming all the yeast in a Wyeast packet are viable (only about 25% truly are!), we are adding only 50 ml of about 60 million/cells per ml. This translates into a pitching rate of 150,000 cells per ml (Table 4). Thus with a single Wyeast packet you are underpitching by a factor of at least 35 for ales and almost 100-fold for lagers. What is the big deal about underpitching? Well remember that very little yeast growth should go on in the fermenter. There should be no more than 3 or 4 cell division which should take place during the first few hours of fermentation. If underpitched the yeast will spend much more time trying to grow to adequate quantities. During this extended growth period the yeast tend to secrete more esters and fusel alcohols. Moreover they may not have a sufficient number to adequately metabolize (digest) all of the fermentable sugars. So what you end up with is a beer with off-flavors (such as esters, fusel alcohols, diacetyl, acetaldehyde) and a high finishing gravity. Thus it is important to always make a starter and make it a relatively big one. Remember that you want the yeast to spend most of their energy making alcohol not babies in a fermenter!!

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