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1) Beer contamination may be detected by smell and taste alone. 2) One can tell if a heat exchanger is sanitary by taking it apart and looking at it. 3) The best place to store yeast is in a cold fermentor cone under finished beer. 4) A sample can be checked for contamination by examining it under a microscope. 5) Lactic acid bacteria are the most common and troublesome brewing bacteria. 6) Equipment need not be tested for contaminants if it is judiciously cleaned and sanitized. 7) Consistent pitch rates are attained by controlling the weight or volume of yeast pitched. 8) Wort oxygen levels begin to drop only once fermentation begins. 9) Re-aerating a "stuck" fermentation is always a bad idea. 10) Diacetyl is produced by various yeasts in varying quantities.
1) FALSE One cannot always tell if beer is contaminated by smelling and tasting it. In fact, our random sampling of very tasty and drinkable microbrews from a local liquor store revealed that more than half of them contained contaminants! Almost all of these contained enough bacteria to eventually affect flavor and shelf-life. We should not trust our tongues and noses to detect the by-products of a few organisms in a vast wash of flavorful drink. 2) FALSE Taking a heat exchanger apart and inspecting it may show you some things, but it will not reveal the presence of microbes. But, there is an easy way to tell whether or not it is a hot bed of contaminants. Simply sample some wort from the effluent side into a sterile sample tube, cap it and let it sit around for a couple of days. Bubbles and cloudiness indicate the presence of microbes. A clear, gas-free sample is proof-positive that the heat exchanger is sanitary. 3) FALSE Storing yeast in the fermentor cone under beer is far from ideal. To yeast, beer is a nutrient-poor waste product, and forcing it to reside there will cause the viability to drop precipitously (up to 50% within 48 hours), no matter how cold it is kept! Click here for complete yeast care information. 4) FALSE One can rarely tell if a sample is contaminated by examining it under a microscope. This has to do with finding the proverbial needle in a haystack. If you put a drop of yeast, wort or beer onto a slide and are able to find bacteria after examining a few fields, the contamination level is very high. We have found that pitched wort containing 20,000 Lactobacilli per ml (as revealed by plating on growth media) showed no evidence of contamination when examined under a microscope! 5) FALSE Pediococcus and Lactobacillus have gotten a lot of press as the cause of much ruined beer, but so-called wort spoilers are found more often. They frequently cause problems in "unlikely" places such as bottled beer, and some produce copious quantities of DMS and diacetyl. It is wise to test for all brewing bacteria on a regular basis. 6) FALSE Being diligent with a good cleaning/sanitizing regime does not guarantee that equipment is free of organisms. Drain a little post-CIP liquid onto a plate of bacterial media, or streak from hard-to-reach areas with a sterile swab. Growth of any kind means you aren't getting your system clean. Trying hard is no guarantee of success ... be sure to give your regime the "acid test". 7) FALSE Adding yeast by weight or volume is not the best way to ensure consistent pitching rates. First, the amount of beer caught along with the yeast will change from crop to crop, so slurry density will vary. Second, viability is not being considered. If the viability of the previous crop was 99% and this one is 90%, the effective pitching rate of the latter slurry will be roughly 1,000,000 cells/ml lower than that of the former. If yeast is allowed to sit in the cone, even at low temperatures, the viability often drops to up to 50% in less than two days. If this is pitched assuming a viability of 99%, the effective pitching rate is off by 3,000,000 cells/ml, and this is enough to affect fermentation performance. The solution is to stain the slurry with methylene blue and run a quick cell count using a hemacytometer and microscope. By dying the slurry first, you allow yourself to differentiate between live and dead cells as you do the count, giving you the effective pitching rate, which is the only meaningful one. 8) FALSE Dissolved oxygen levels in wort drop very quickly. After just two hours, the oxygen has almost entirely dissipated, even when yeast is not present! Of course, the presence of yeast greatly accelerates the drop, and does so way before evidence of fermentation is visible. 9) FALSE If the wort gravity has dropped less than 30% towards its final gravity, it is safe to re-aerate. This is sometimes the only way to recommence fermentation activity. Yeast will remove added oxygen from the fermenting wort, and so the second aeration will not contribute to oxidative potential in the finished product. 10) FALSE Diacetyl is produced in roughly equal amounts by normal brewing yeasts; some strains are just better than others at reducing it to flavor-neutral compounds. The more flocculent the strain, the more likely it is to sink to the bottom of the fermentor before it has had adequate contact time to reduce diacetyl in the beer, leaving detectable levels in suspension.
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