Saturday, January 19, 2013

Original Aeration Presentation


From Wikipedia: Aeration (also called aerification) is the process by which air is circulated through, mixed with or dissolved in a liquid or substance.

Aeration of liquids (usually water) is achieved by:

  • Passing the liquid through air by means of fountains, cascades, paddle-wheels or cones.
  • Passing air through the liquid by means of the Venturi tube, aeration turbines or compressed air which can be combined with diffuser(s) air stone(s), as well as fine bubble diffusers, coarse bubble diffusers or linear aeration tubing. Ceramics are suitable for this purpose, often involving dispersion of fine air or gas bubbles through the porous ceramic into a liquid. The smaller the bubbles, the more gas is exposed to the liquid increasing the gas transfer efficiency. Diffusers or spargers can also be designed into the system to cause turbulence or mixing if desired.

For Homebrewers: Adding dissolved oxygen to cooled wort for the benefit of the yeast.

Why aerate your wort?

Healthy happy (California) yeast make good tasting beer.

o    Too little dissolved oxygen results in
        • Low and sticky fermentation
        • Off flavors
        • Poor yeast crop
        • High ester production, resulting in a fruity-tasting beer
        • Low alcohol production
        • Better opportunity for unwanted wild yeast and bacteria to dominate wort

o    Too much oxygen causes

§  Rapid fermentations, resulting in excessive yeast growth and beer losses

§  Low ester

Yeast need to synthesize sterols (fatty acids) that are not normally available to them in the wort. When they have done this, their outer membranes are permeable thus allowing the sugars in the wort to be digested so alcohol and carbon dioxide can be created. Note: Olive Oil contains the very same fatty acid the yeast are trying to synthesize. Yeast can also use some trub to help in the synthesis of the needed sterols.

Fermentation and propagation\reproduction take energy. The yeast must build up their energy stores and grow\bud until they reach the proper density to start switching from aerobic to anaerobic metabolic pathway usage. Alcohol is a byproduct of anaerobic metabolic activity. Aeration helps yeast build up their initial energy stores to accomplish both of these main tasks.

When is the best time to aerate your wort.
  • After the boil, once the wort has been cooled to pitching temp.
  • Aerating the wort as it enters the chiller increases cold break and darkens the beer.
  • Aerating wort with yeast already pitched into it can be beneficial depending on method of aeration
  • After the wort has been fully cooled for lager fermentation and the settled trub has been removed or minimized.
When is the wrong time to aerate your wort?
  • Aerating hot wort can set off staling reactions – some controversy on this theory
  • After fermentation has already started as this can stall fermentation as the yeast switches back to aerobic metabolic pathways again. Need to be careful if racking to secondary.
  • Aerating fermented wort can cause alcohol molecules to cause stale tasting aldehyde molecules.

 Aeration methods

  • Splashing wort – easy and no cost
  • Use of Venturi device – easy and minimal cost
  • Oxygen stone with air pump in conjunction with a sterile filter – much quicker infusion of DO for a moderate cost.
  • Oxygen stone with tank of pure oxygen - Very quick infusion of DO with slightly higher cost.
  • Household Hydrogen Peroxide – very cheap but cannot be use in wort with pitched yeast Not Recommended! -  See Aeration Revisited

From Wikipedia:

On a given volume of air or liquid, the surface area changes proportionally with drop or bubble size, the very surface area where exchange can occur. Utilizing extremely small bubbles or drops increases the rate of gas transfer(aeration) due to the higher contact surface area. The pores which these bubbles pass through are generally micrometre-size.

Other things to consider
  • One drop of Olive oil will give yeast all the fatty acids needed to develop permeable membranes, but does not help speed the development of energy stores.
  • Aeration can be done multiple times in the first few hours after pitching yeast.
  • Nearly impossible to surpass 8ppm DO unless pure oxygen is used
  • Air is make up of only 21% Oxygen

How much to aerate the wort

·         Target is 8ppm to 12ppm of Dissolved Oxygen (DO). Varies by yeast strain and desired amount of esters contributed to the finished beer. To achieve 8ppm it takes:
    • About 30 minutes of shaking a fermenter manually
    • 15 minutes with air pump and aeration stone
    • 20 seconds with tank of pure oxygen and aeration stone - 15 ppm in 80 seconds
    • 2/3 to 1 ml of hydrogen peroxide per gallon of wort about 20 minutes before pitching yeast. Not Recommended! -  See Aeration Revisited
    • You’ll get about 4ppm just by allowing cooled wort to drain into fermenter using a siphon spray attachment on the end of the hose.

My Recommendations;
  • Clean\non-fruity  Ales (Most English and American ales) High DO (10 to 12),
    • Med. Pitch Rate (1/2 gal. starter / 5 to 6 gallons wort) & Med to Low Fermentation Temp 70 to 64 degrees 
  • Fruity Ales: Med DO, Med Pitch Rate (1/2 gallon starter pre 5 to 6 gallons of wort) &
    • Med to High Fermentation Temp. (72 to 85 degrees
  • Lagers: High DO (12+), High Pitch Rate (1 gallon starter per 5 to 6 gallons wort) &
    • Very Low Fermentation Temp 40 to 50 degrees
  • High Gravity beers; increase DO, increase pitching rate, use highly attenuative yeast strain, and allow fermentation temp to rise as fermentation finished, rouse yeast by swirling wort in fermenter as fermentation slows.
  • Too much DO can actually kill all character from the yeast. Example – WL English Ale yeast with 5ml HO3 in 6 gallons and fermented at 66 degrees is nearly flavorless. Using 3.5 to 4 ml in the same size batch and fermented at 67 to 68 degrees is a nearly perfect balance while fermented at 74 the esters will dominate.

Pitch enough yeast, feed them and aerate them well and keep them in a cool dark place and they’ll reward you with a flavorful beer that has a balance of character from the raw ingredients and your hand in steering the yeast to add just enough of their own special flavors

 Once you master these basic rules you can start bending the rules to make truly unique beers!

Information Sources

  • Books;
    • Principles of Brewing Science (1st ed.) by George Fix
    • An Analysis of Brewing Techniques by George & Laurie Fix
    • How to Brew (1st ed.) by John Palmer
    • Yeast by Chris White and Jamil Zainasheff

 Aeration and beer flavor

                Aeration is part of a pyramid that determines the majority of your beers flavor along with Pitching Rate and Fermentation Temp. These three components determine how your yeast will attenuate the wort and what flavor compounds they will contribute to your beer.

How temperature affects rate of oxygen going into solution from aeration

*You can see that it is nearly impossible to oxygenate very hot wort but the cooler your wort, the more susceptible it is to oxygenation.

How to calculate starter size to get the right pitch rate

750,000 x Volume in liters x Original Gravity in Plato

5.25  gallon of wort in your fermenter is about 20 liters.
If your O.G. is 1.061 that would be about 15 degrees Plato. 

750,000 x 20 x 15 = 225,000,000 yeast cells

1 comment:

  1. Your post about venturi tubes is really informative & explanation with the diagram makes it easier to understand as well. I also read a post about Things to Consider Before Placing an Order for Venturi Tubes from Los Angeles based venturi tubes manufacturer. Hope it helps you & your readers as well.