Oxidation

[niall]

Sorry to start this whole mash/boil oxidation/HSA debate all over again but I've had a problem with a few of my all grain beers and I haven't quite been able to pin it down - until now. It's been in primary for 2 weeks and as I was taking a taste test last night prior to kegging I made my discovery. This time the flavour is stronger and it has that 'sherry' taste so I can only presume it's oxidised.

This is my process if anyone can spot any obvious flaws:

* Fill cooler mashtun with strike water, add grains and mix thoroughly
* Mash for 1 hour
* Add infusion water to compensate for grain absorption. This was added from the Hot Liquor Tank (Burco-type boiler) through a syphon hose which i ran onto an upturned plastic plate on top of the grain bed to minimise splashing. (maybe i should just place the end of the syphon under the surface of the water?)
* Recirculate into 2 litre jug and pour gently over grain bed (again on top of plate). Repeat
* Stir grain and open tap to run off into boiler through syphon hose
* Add sparge water using the same method as above, rest, stir, recirculate and run off using the same methods as above.

Is it possible that it's picking up oxygen in the syphon hose? I start off by opening the tap slowly and after recirculating I gradually turn it until it's open fully.

When adding hops during the boil I stir the wort with a plastic spoon.

One other thing I should mention is that the previous brew is showing signs of oxidation, although not as bad - I roused the yeast with that brew so maybe I introduced oxygen during fermentation - is it possible that oxidation flavours would carry over through yeast slurry??

[steve_flack]

I think that generally you're taking pretty much the same precautions as most people. In any event it seems that HSA may not be a huge issue for most homebrewers as it seems you really have to go some to oxygenate the wort so badly that it crops up.

On the other hand 'sherry' flavours are usually as a result of oxidation (as is 'cardboardy').

[delboy]

might well be that you have a lower taste threshold for the compounds formed by oxidation, let some of your friends taste and see if they notice anything.

I think the first AG batch i did is oxidised, it has a funny cardboardy taste which is more noticable when i burp , i had put it down to the co2/N2 gas mix at first (because of the burping thing). Now i reckon it was because i tried to force carbonate this (purged 3 times then shook the hell out of it when conected to the gas) must have had a tiny amount of O2 still in there to do the damage.
Lesson learnt no more force carbonation nonsense.

[niall]

This has me stumped. With another brew some people tasted this (less noticeable) flavour and some didn't notice - with this brew your taste buds would have to be dead not to detect it - it really is that strong.

[UserDeleted]

I hate to get involved in this as people have told me time and again that it doesn't happen. . . . . .

If you are tasting 'sherry' like flavours then you are looking at cold side aeration. 'Sherry' flavour/aroma is down to acetyaldehyde (most commonly) which is caused by oxygenation of ethanol, so at some point you are adding air to your beer once fermentation has started.

You don't say if you drop, bottle, keg, flush the keg, but I would certainly look at your fermentation/post fermentation practices to try and nail this one.

There is one other possibility and that is infection. I'd have to check but I am sure that there are some WSO's (*) that can 'oxidise' alcohol to produce acetaldehyde. Of course its easy going the other way where acetobacter produces ethanoic acid by reducing ethanol

(*) Wort Spoilage Organism

[niall]

Maybe this is what I need to look at because I don't think my mash/boil procedure is that different to others.

I suppose in that case there are a couple of possibilities: If I rouse the yeast by shaking the fermenter or by stirring with a plastic spoon, maybe this might be introducing oxygen - or as you say, maybe it's an infection and I need to take a closer look at my sanitation procedures post boil?

With this brew I didn't rouse the yeast but I was reusing yeast from the previous batch where I did rouse it, dunno if that's a factor, I wouldn't have thought so. On the other hand if the previous brew was infected the yeast would have carried that over into this one...

[steve_flack]

If you are tasting 'sherry' like flavours then you are looking at cold side aeration. 'Sherry' flavour/aroma is down to acetyaldehyde (most commonly) which is caused by oxygenation of ethanol, so at some point you are adding air to your beer once fermentation has started.

You don't say if you drop, bottle, keg, flush the keg, but I would certainly look at your fermentation/post fermentation practices to try and nail this one.

Do you rack to secondary? The reason I ask is that most yeasts are pretty good about tidying up any acetaldehyde after fermentation. Racking too soon might leave some acetaldehyde?

[niall]

You don't say if you drop, bottle, keg, flush the keg, but I would certainly look at your fermentation/post fermentation practices to try and nail this one.

Mostly I keg, sometimes I do secondary, sometimes I don't bother. I tend to flush the secondary with CO2 and I always purge the cornie with C02 so I'm guessing if it's cold side aeration it must be during fermentation.

edit: If I do rack to secondary it's never sooner than a week or 10 days.

[niall]

If the connections on your transfer tubing aren't secure you can get o2 ingress that way.

That's interesting, the tubing is a loose fit on the lever tap on the mashtun and it twists as I open the tap.

Good tip on the purging the cornie, I'd never thought of using the liquid connect. What do you mean by purging fermenters from the bottom?

[delboy]

If the connections on your transfer tubing aren't secure you can get o2 ingress that way.
While i've no doubt HSA is something that can occur in theory it's very difficult to achieve. I've done everything you aren't supposed to do to a mash before and it's been fine. I made Phils Heffe in the Autum, the mash got stirred and transfered around and the run off was splashed about as I ran off into a bucket and just dumped it into the boiler I had ran out pf patience at this point. Despit that, there's a few pints sitting in a corni as I type, as good as every (albeit crystal clear now).
My minimashes get pretty badly abused also and i've kept those for several months with not sign of oxidation either.

btw when you purge your corni (my theory at least) is it's best to add co2 from the liquid in and purge out through the prv, like wise purge fermenters from the bottom also (i've done this a few times but I reckon this is over kill).

Just to clarity DaaB are you saying you can use this method to purge cornies full of beer as well as purging an empty corny before transferring the beer to it???

[delboy]

No, just to purge alot of the o2 prior to racking.

ok, i guess that makes sense, i've seen on the american forums that some prefer to force carbonate using the liquid out post (works better apparently) but it does tend to make a mess when you pull the gas back off it.

[Matt]

As the thread still sounds inconclusive I wondered if you are fermenting high and creating excessive fusel alcohols Niall?

I fermented a Hefe in a too warm cupboard (shooting for the banana flavours) and it tasted like it had sherry in it.

Also found this link which cites other factors.

Matt

[niall]

Hi Matt,

Ferm temps were around 20-22 so I don't think the problem lies there. Someone suggested that a low mash temp could cause this problem. I mashed at 64 and it dropped around 1 degree over the course of an hour - that doesn't sound too low, does it?

I haven't discounted the possibility that I'm not diagnosing the flavour correctly and it's an infection...

[niall]

Either stick your co2 tube right at the bottom of the fermenter when you purge or connect it to the fermenter tap.

Ah, OK, as simple as that - I did wonder if I was missing something more complicated. I like simple solutions