I did a lot of reading about
Hot Side Aeration for a presentation at London Amateur brewers. I found was that there is very little scientific information available to the homebrewer about this, most of the discussion is still held in the journals. The forums contain a lot of hearsay with nobody actually supporting views.
The main impression I got was that the science behind the issue is sound, so it can have an affect. However, it is a very complex issue with many other factors affecting beer stability as well. The most interesting 'article' I found (which really supports this view) is an interview with "Dr. Charles Bamforth on
hot side aeration with Jamil and John Palmer".
http://www.thebrewingnetwork.com/shows/475.
The best tip I came across was that
aeration is far more of a problem in secondary / bottling so if you are worried start at the end of your brew and work backwards. Most things to put in place are easy and cheap, such as a pipe from mash tun to boiler, so I just do them anyway.
At the bottom are a list of freely available articles on the internet. If anyone would like my complete document PM me
Here are a list of tips from that literature for avoiding in the homebrew environment, however, some are contradictory:
Preventing in the home brew environment:
Mashing
The grain in the mash should be underlet or infused with
hot water from the bottom up. By infusing in this manner, stirring of the grains to insure uniform mixing of the grain and
hot water is not necessary. By not stirring the water into the mash,
hot oxygen reactions can be reduced. (Millspaw, 1992)
BYO recommends the following technique. Add 3L of water to the mash tun, then carefully add 1kg of malt and gently mix malt into water. Continue this process until all of the malt and water has been added. This process will take longer so be sure to adjust for temperature losses
Palmer (2006) recommends adding water a gallon at a time (to all of the malt) and gently mixing the water in without aerating. He states that HSA is promoted by lipoxygenase at this stage, although as Fix sates the levels required by this reaction are very low.
Millspaw (1992) recommends adding specialty malts only in the mash out. The melanoidins formed at 77°C/170°F are more stable than those formed at the lower temperatures of conventional mashing. By adding these specialty malts only in the mash out, the brewer can make his mash more efficient by optimizing saccarification, maximizing the formation of melanoidins. This will lead to smoother and rounder flavours from the specialty grains, as well as more stable and clearer beers (Millspaw, 1992).
Mash recycling tends to remove a lot of large particulate matter that would otherwise be present in the boil. Millspaw (1992) feels that these techniques are a source of HSA and that the particulates (husks and grits mostly) provide a place for proteins to clump onto during the boil and then settle out more effectively in cooling.
However, Fix emphasises that one of the most important points it achieving reasonable wort clarity in lautering (Fix, 1999).
Transferring to the boiler
In practice if the power is switched on immediately the heating element is covered any uptake of oxygen is immediately driven off by the action of the boil (Alexander, 2009). Personally, I now collect using a tube into a 5 gallon bucket and then siphon from my collection vessel into the boiler.
Post Boil
Older books used to advocate pouring the boiling
hot wort from one bucket to another to add oxygen and cool it. Unfortunately, the wort is still
hot enough to oxidise and not aerate. Pouring down the
side of the bucket to minimise splashing doesn’t help either since this increases the surface area of the wort exposed to the air (Palmer, 2006). Ensure the wort is below 27C before aerating air (Palmer, 2006)
Storage
In fresh beers both T-2-N and its precursors are bound up with natural sulphur compounds from yeast metabolism. However, after a lag, which is reduced if thermal or mechanical abuse occurs, the effects of T-2-N become discernible. Millspaw (1992) and Bamforth (2009) also emphasise the importance of storage temperatures. The Arrhenius equation shows that for every 10C rise in temperature a chemical reaction will perform 2-3x faster. For example if you store a beer at 20C a beer may stale in three months. A stored beer at 30C will stale in one month.
Additives
Additives could be one solution, however, the effective additives tend to have unacceptable
side effects and the neutral ones rarely seem to work (Fix, 1999). The most likely additive to be of any use in the home brew environment is Potassium Metabisulphate (Campden Tablets) added to the mash (Fix, 1999, Spencer, 2006) which binds to carbonyl compounds. These haven’t gained favour in the commercial world because above certain 10ppm levels they must be stated on packaging and we “can let the wine have that dirty labelling†(Bamforth, 2009). It may therefore be an option to us, the bisulphates will bind to the staling aldeydes and masks their presence. However, these bonds are rather short lived in beer, and when they are broken, the staling aldehydes fully reveal their presence (Fix, 1999)
Summary
The effects of oxygen pick-up after fermentation are more apparent and severe than the effects of
hot-
side aeration. If you are thinking about changing your brewing procedure to avoid oxidation, you should begin addressing oxygen pick-up from the end of the process and work your way forward toward mashing (BYO). It is a complex interplay of reactions, including unsaturated fatty acids, melanoidins and iso-alpha-acids. It is therefore too simplistic to focus on just T-2-N as the sole cause of staling in beer (Bamforth, 1999).
References
Alexander, J (2002).
Hot Side Aeration (HSA). Brewers Contact. 9, 2-5. Also published at
http://www.craft brewing.org.uk/bc/backissues.html
BYO.
http://www.byo.com/stories/techniques/a ... -mr-wizard
Bamforth, C. (2009).
Hot Side Aeration. The Brewing Network
http://www.thebrewingnetwork.com/shows/475. Start at 13 minutes
Fix, G. (1999). Principles of Brewing Science, Second Edition. Brewers Publication (sorry not on the internet)
Garrod, P. (2008).
Hot Side Aeration. Brewers Contact. 8, 4-5 Also published at
http://www.craft brewing.org.uk/bc/backissues.html
Spencer, J. (2006)
Hot Side Aeration Exeriment 02/11/06. Basic Brewing radio.
http://www.basicbrewing.com/index.php?page=60
Millspaw (1992).
Hot Side Aeration and Beer Stability. Zymurgy. 15. Also published at
http://oz.craft brewer.org/Library/Methods/Other/HSAmash.shtml
