Jamil Show: Oxygenation

[marnold]

I was listening to the Jamil Doppelbock show yesterday and was surprised to hear him mention that too much oxygenation can have a negative effect on flavor, because too much yeast is grown, etc... which was a little surprising to me.

So that begs the question, how much oxygen is the right amount, and how much is too much?

I haven't ever oxygenated, but I'm about the start with my next batch to hopefully help start fixing some chronic under-attenuation problems.

Thanks!

[boobookittyfuk]

it depends....



for most cases, 8ppm oxygen is good.....what? you can't measure oxygen in ppm??? me either.

there are way too many factors to give a generalized...sort of...like if you pumped pure oxygen with a 2 micron stone for 43 seconds, you'd get 8ppm...they're too many factors such as: temperature, pressure, viscosity, flow rate of gas, size of bubbles, contact time of bubbles with liquid, gayness of JP, lunar phase, atmospheric pressure, oceanic tide shift for madagascar, whether BUB will ever change his avatar, size and shape of vessel, and so forth.

i usually pump about 1/2-3 minutes of oxygen depending on which of the above factors are determining.

[BadRock]

This is quoted directly from BYO's Mr. Wizard column. I found it rather informative. Hope it helps.


Is it possible to aerate your yeast too much?
"Dear Mr. Wizard,
How long would I have to aerate with oxygen in order to incur negative effects on my yeast? I have read several articles that skirt the issue, but most cover commercial brewing and don’t give homebrewers an idea of how much is too much. I have read the recommended length of time to aerate, but not the maximum times.
Perry Launius
Jackson, Mississippi

Mr. Wizard replies: It sometimes seems like homebrewing has advanced from “Relax, don’t worry, have a homebrew” to “Stress out so much that only a homebrew can calm you down.” (Nothing personal! Just an observation based on seven years of Wizard questions.)

Unfortunately, there is no exact answer to this question. To leap-frog to my recommendation, I encourage homebrewers to worry more about under-aeration and not to spend too much time on concerns with over-aeration. The caveat is with propagation. Yeast can be stressed when oxygen is continuously or intermittently bubbled into a propagation container. I will give some insight that may help understand why there is no exact answer to your question and will present a list of facts about oxygen and yeast that may help.
For starters, not all brewing yeast strains have the same oxygen requirements for satisfactory fermentation. This observation is documented in Malting and Brewing Science, Volume II (Hough, Briggs, Stevens and Young), although many practical brewers know this to be true from anecdotal evidence. This book has a very nice graph showing peak yeast density as a function of wort oxygen content at the beginning of fermentation. The graph shows a dramatic increase in yeast density as oxygen levels increase from 0 mg/L (which equals 0 ppm) to 2 ppm and very little change from 2–8 ppm. Another graph shows the relationship between the duration of fermentation and wort oxygen content at the beginning of fermentation. This relationship is a bit more interesting since fermentation time decreases as oxygen content increases.
In the book Brewing (Lewis and Young), the point is made that alcohol content in beer declines as wort oxygen levels increase. This reduction can be greatly exaggerated in fermentations that are continuously aerated, such as yeast propagation. Cell density in a commercial propagator with aeration and stirring provisions can reach as high as 200 million cells/mL; this is about five times higher than the peak density seen in a typical beer fermentation where the fermenter is neither aerated nor stirred.

The explanation for this phenomenom is relatively simple — alcohol is not produced from glucose when yeast are consuming glucose to synthesize the building blocks for new yeast cells. Wort aeration also has a dramatic influence on beer flavor formation during fermentation because it affects yeast metabolism. For example, if wort oxygen is limited then ester production increases and, in turn, the production of fatty acids within the yeast cell is limited. Likewise, fatty acid production increases with wort oxygen level and ester production decreases.

Yeast propagation is really the place in commercial breweries where over-aeration has been examined. Why? Because yeast propagators are equipped with sparging devices designed to deliver a lot of air to the propagation and increase cell growth. After all, the goal of propagation is growing yeast and not making beer. Both practical brewers and brewing scientists have observed that yeast can be damaged when excessive amounts of oxygen are delivered during propagation. The term used to describe this stress is “oxidative damage.” While oxygen is required for a wide array of biochemical functions, it is also related to cellular aging. The free radical theory suggests that cellular aging results from damage caused by reactive oxygen species known as “free radicals” — sounds like a punk rock band!

Veronique Martin of Oxford Brookes University presented a poster at the 1999 European Brewing Congress (EBC) in Cannes entitled “The Oxidative Stress Response of Ale and Lager Yeast Strains.” This poster showed stationary phase yeast (the phase after the increase in yeast density) to be less sensitive to oxidative stress than cells growing during the exponential growth phase. Furthermore, the negative affects of oxidative stress show up in subsequent fermentations that use yeast cropped from a stressed environment.
At the same EBC meeting, Chris Boulton from Bass gave a talk called “A Novel System for Propagation of Brewing Yeast.” This method uses oxygen injection into the propagator, but the oxygen flow is regulated using a mass flow meter and oxygen measurement within the propagator to maintain a level of oxygen not exceeding 0.5 ppm. The propagator is also slightly pressurized with nitrogen to minimize foaming. The purported advantage of this method is that yeast is not exposed to oxidative stress during the sensitive growth phase of their life cycle.

This is clearly a topic without an exact answer as research is ongoing. In fact, much of the research is believed to relate to aging in humans and other animals. I will close with a list of facts and my own opinion.
Fact: Wort oxygen levels very quickly drop after the lag phase of fermentation ends when aeration or oxygenation is performed only once. This is the typical method of aerating wort.
Fact: Wort has an oxygen content of about 8.5 ppm when saturated with air (79% nitrogen and 21% oxygen) and an oxygen content of about 43 ppm when saturated with oxygen.
Fact: 0.57 liters of oxygen at standard temperature and pressure weighs 813 mg. When dissolved in 5 gallons or 18.8 liters of wort, this results in a concentration of 43 ppm. After the saturation point is reached, no more oxygen can be dissolved into wort. In other words, it doesn’t take long to saturate wort with oxygen (or air when aeration is being performed).
Fact: Oxygen content in wort cannot be known without measuring it since wort temperature, gas bubble size and the contact time between the bubble and wort all have a profound effect on gas diffusion. Small bubbles diffuse much, much more quickly than big bubbles. Small bubbles also are less buoyant, rise slower through the wort and as such have a longer contact time. That’s why aeration stones are designed to produce very fine bubbles.
Fact: The major concerns with commercial brewers and over-aeration are primarily focused on propagation where aggressive aeration/oxygenation can cause problems due to oxidative stress.
Opinion: This topic has incredible depth and becomes extremely confusing if one attempts to create a Unified Theory of Aeration. There is no exact answer to your exact question. Homebrewing is a hobby of exploration. I think the idea is to learn from what others have done and explore the art of brewing in a fun and creative manner. Along the way, the experienced brewer will come up with their own special techniques and interpretations to the tremendous number of ideas floating around the brewing (and homebrewing) world.

I personally use pure oxygen for a one-time saturation shot for yeast propagation. I have never had any problems with this method. When it comes to wort aeration for making beer, I use air and saturate with air. Again, this works well for me and, most importantly, my yeast! "

[jamilz]

The thing to do is to measure the amount of O2 you add by time and flow rate. Keep it consistent. Pretty soon you'll build a standard. Then try doing a number of batches with more O2. See if that helps or hurts. Then try a series of batches with less O2. Same thing.

The right amount depends on so many factors, you can't say X amount. Let the beer tell you how much is the right amount of O2.

[smurfe]

Working in EMS I was able to "acquire" a medical oxygen tank and regulator. In the past I have just put the Mix-Stir on my drill and gave the wort a few shots with the drill to oxygenate.

Now with the pure medical grade oxygen, what level of flow (liters per minute) from the tank would I use and how long on average does one aerate? The regulator goes from 0.5 liters per minute to 35 liters per minute. Do you just dip the hose with the stone on it in the wort and let it go or do you kind of stir it around the wort to distribute the oxygen through the wort?

Thanks in advance.

[JJFlash]

I also use a medical oxygen set-up.
0.125 liters per minute for 30 minutes is my current rate.
Only reason in the world I chose this is because by 30 minutes the foam is up to the neck of my 6.5 gallon carboy, just enough roon to pitch the yeast.
On my big beers, >1.080, I hit the primary carboy for one minute at 0.5 liters per minute for 2 -4 times in the first 24 hours with additional oxygen.
However, I am not sure all this exact timing is either good or bad.
I need to brew another couple hundred batches of beer with additions of more or less oxygen before I can dial into the exact correct amount for perfect fermentation.

[Colin Kaminski]

I like the post from Mr. Wizard. There are much larger problems from under oxygenating than over oxygenating. However I have found there to be problems with over oxygenating as well. I find the beer character is thin and watery. I also grow too much yeast wich makes seperating it out more time consuming. Also, the ester profile changes. With the three strains of ale yeast I use it tends to make less esters, something like fermenting colder would. The amount of O2 I use is different for each of my three strains.

Make sure to add some O2. If you have 2 carboys from the same boil try adding lots of O2 to one and no O2 to the other to see the difference.

[DBear]

Has anyone experienced a difference in yeast preformance between oxygenating the wort first then pitching or pitching into the wort and then oxygenating?