Tag: learning

For ales, these sulfur-compound issues tend to disappear. For example, ale malt with only 1 μg of SMM per gram of malt is common. This low initial concentration means that the SMM level at the start of the boil is

This initial SMM concentration leaves a SMM residual of

at the end of the boil. As noted above, 50% of the sulfur-containing compounds (be they SMM or DMS) is removed in the fermentation. Thus, the finished beer will have sub threshold levels of DMS no matter how the wort is cooled. Indeed, any hint of DMS in ales is likely from technical brewing errors, most notably contamination (see chapter 3). This fact probably explains why ale aficionados react very negatively to DMS in any type of beer.

Once the wort is chilled to pitching temperature, it needs to be effectively, but not overly, aerated. Most home brewers will not have the budget for a digital oxygen meter (unless you really have a serious bank account and are a possessed brewer). The dilemma of using pure oxygen versus aeration via agitation is easy to resolve. Use aggressive shaking if you are strong enough to do so. If it is too heavy for you, then use pure oxygen. It is easy to over-oxygenate the wort in a small vessel with pure O₂, so tread carefully. Levels of oxygen over 12 mg/l can have a toxic effect on the yeast and result in stopped fermentation.

Methods of Aeration / Oxygenation

Homebrewers have several aeration/oxygenation methods available to them:  siphon sprays, whipping, splashing, shaking, pumping air through a stone with an aquarium pump, and injecting pure oxygen through a sintered stone.  We have tested all of these methods using a dissolved oxygen meter and have found that, when using air, 8 ppm of oxygen in solution is the best that you can achieve.  Injecting oxygen through a stone will allow much higher dissolved oxygen levels.  The chart below shows methods tested and the results.

Method	DO ppm	Time
Siphon Spray	4 ppm	0 sec.
Splashing & Shaking	8 ppm	40 sec.
Aquarium Pump w/ stone	8 ppm	5 min
Pure Oxygen w/ stone	0-26ppm	60 sec (12ppm)

It was concluded that pumping compressed air through a stone is not an efficient way to provide adequate levels of DO. Traditional splashing and shaking, although laborious, is fairly efficient at dissolving up to 8 ppm oxygen. To increase levels of oxygen, the carboy headspace can be purged with pure oxygen prior to shaking. The easiest and most effective method remains injecting pure oxygen through a scintered stone.