This year it was on how Ageing Flavours Begin in the Mash Tun*.
|Continuing Professional Development|
The cardboard flavours found in ageing beers are caused by carbonyl compounds created during the brewing process. They cannot be tasted early on as they are bound in chemical complexes. They come from the oxidation of fatty acids to aldehydes in the mash tun and downstream and lipoxidases having a similar effect if there's a protein rest. Strecker reactions can also cause aldehydes to be formed from amino acids. Maillard reactions are also involved.
To minimise formation of staling compounds oxygen ingress should be kept to a minimum during brewing. CO2 purge the mash tun, bottom fill the copper and use deaerated liquor for mashing. Having a valentine arm or variable speed pump on the mash tun is better than partially closing a valve as this causes a partial vacuum in the pump and encourages DO pickup. Don't over oxygenate wort, and oxygenate it when the yeast is ready to grow.
Higher mash temperatures slow down lipoxidase activity, so use well modified malt that doesn't need a protein rest. Also this will reduce TSN which is a substrate for Stecker aldehydes.
Aldehydes are more soluble in alkali solutions so acidfy sparge liquor to pH5 (using lactic acid) and get the CaSO4 right for the mash. Aldehydes are loosely bound so a good boil strip them out, get at least 7% evaporation. Keep whirlpooling to a minimum. Good trub formation will also help pull out aldehydes.
Maltsters can also help by suppressing rootlet growth and Null lox malt is also available which is made from barley which has had a staling enzyme bred out of it. Keep copper and iron levels low in the brewhouse as they encourage oxidation, and remember that yeast only mops up oxygen during maturation if it's at at least 12 degrees C.
Fascinating eh? Now back to the beer:
One highlight was managing to track down the revived version of Draught Burton Ale. It wasn't a bad effort, and they've certainly got the hops right but it was a bit dryer and lacked the slight sweetness than Burton at its best had.
|Maybe if I crop this enough people won't notice it's an old picture from a pub|
* Based on the paper "On the Origin of Free and Bound Staling Aldehydes in Beer" Baert, JJ et al. Jouranl of Agricultural and Food Chemistry, 2012.