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Old 06-14-2014, 04:11 PM   #1
skw
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Default Acetaldehyde? Lacto?

I have an off-flavor that I'm not sure if I'm identifying it correctly: it doesn't taste like green apple as in Granny Smith from the supermarket, it tastes like apples that aren't ripe yet - a kind of slightly sour, tart taste, maybe a bit similar to red currants or dry white wines.



It showed up after ~3 weeks in the bottle, before that it may or may not have been masked by yeast in suspension. It definitely did not show up when I tasted at bottling time.



The brew is:
19L
13 plato

4.5kg Munich Malt

60g Spalter Select FWH

Pitched one packet of rehydrated Nottingham yeast into 17°C wort

Fermented at 15°C measured by fermometer

bottled after 10 days in primary



Now the odd part is that I've had this flavor once before, but at a completely different brew: 18 months ago, using a pre-hopped no boil kit which I pitched, in hindsight, much too warm.



Now I'm wondering what this could be - is what I'm tasting the "green apple" young beer or am I tasting a lacto infection?

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Old 06-16-2014, 08:35 PM   #2
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Could be acetaldehyde witch I would say can taste cidery or like a dry white wine. Three most common causes of acetaldehyde would be premature racking off of yeast, unhealthy ferment or oxidation while bottling or racking. Sometimes it will age out but if it's from oxidation it won't get any better. Good luck!

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Old 06-17-2014, 03:19 PM   #3
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Thanks. Let's hope it's acetaldehyde that will age out. One thing I skipped with this batch that I typically do is raise the temperature towards the end of the fermentation, and I have never used Nottingham yeast before. I could find threads where people claim Nottingham can give a tart flavor, but most seem to agree that Nottingham is very clean and neutral.

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Old 06-17-2014, 03:28 PM   #4
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10 days in primary is a pretty fast turn around. I'm guessing thats where your problem lies. Warming the fermentor would have helped. How long has it been in bottles now?

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Old 06-17-2014, 05:52 PM   #5
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Bottling process (fill bottle in a bucket, place cap on, allow bottles to foam over while filling other bottles, cap on foam to make sure you're not just sealing in O2, ie. don't rush. 2-step cleaning process for bottles, caps, tubing, etc. sanitize primings before bottling),

Infection or weak fermentation - with an overnight mash you've got lots of time to introduce spoilage organisms; check pitch rate for your gravity (find online calculator), you might benefit from doubling the number of packets (so Sacc. yeast can overcome other bugs), be sure you're not shocking the yeast (or you can cut the viable count by half) - dry yeast gets sprinkled on wort and left the heck alone, don't stir or shake it in - if you're struggling with infection and yeast health, rehydrating is introducing another point of contamination and loss of vitality;

make sure yeast is NOT straight out of the fridge, wort and yeast should be within 5 degrees F of each other at pitching, and you ought to cool both to the target fermentation temp before pitching - major flavor-active compounds are produced in the first 48 hours, acetaldehyde and esters both increase with increased temperatures, and it's generally desirable to allow yeast to warm from pitching rather than cool (or fluctuate, which is what your crew probably did) to limit off flavors and encourage attenuation;

sanitize scissors and pack before cutting open the yeast pack.

Check your pre-pitch oxygenation procedure, low O2 = stress, and wort can be very depleted after boil which will encourage acetaldehyde production.

Lastly: I agree, leave it on the yeast for perhaps 21 days until you've got control of the situation.

Curious - what are you priming with?

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Old 06-17-2014, 08:16 PM   #6
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10 days in primary was one of my quicker turnarounds, normally it's a two week primary for me - I realize now what the extra time on the yeast cake is good for, I guess. (It did reach a stable FG though, I swear!)

Pitching rate was 11g of dry yeast for 19L of 13°P wort, the yeast being rehydrated in sanitized water and brought to pitching temperature (17°C) following the manufacturer's instructions - the first time I did that instead of just sprinkling it dry. Left the fermenter alone after that, when I checked on it 24hrs later, it had the usual white foam layer and and a bubbling airlock. This batch was not an overnight mash for a change, this was a regular ~80min mash (albeit on the dry side, 65°C).

Bottling was done by racking onto a boiled and cooled solution of table sugar in water.

It's been in bottles for almost four weeks now, I'll taste one again by the end of this week. If I'm lucky, it has faded, if not, it'll teach me about bottling too early, especially when trying out a new yeast!

In general though, how can I tell the difference between a lacto infection and acetaldehyde? I understand lactos in the fermenter would be visible, but how about bottles? Is there an obvious difference between the two that I can taste?

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Old 06-17-2014, 09:10 PM   #7
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Try finding a beer that was intentionally soured with lacto and give it a taste.

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Old 06-20-2014, 02:26 PM   #8
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Remember that yeast will continue to work after the gravity appears stable (in part by busting up acetaldehyde and such), and that aspects of yeast like flocculation and sedimentation characteristics will affect both primary and clean up fermentation efforts.

Lactic will give a sharp-ish, potentially lemon-ish sourness that you may only perceive in taste, not aroma. Acetaldehyde should be nose-able. Either of those could develop in young beer (lacto is faster to develop than brett, for example). It could also be bacteria like acetobacter that could take off post-bottling, especially if oxygen was introduced - that can lead to ethyl acetate, which is esterified alcohol = acetaldehyde + acetic acid, which becomes vinegary; the overall result is fruity-sweet, dull, bruised apple, and can become sharp and solvent-y.

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Old 06-20-2014, 02:34 PM   #9
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I tried another bottle, and that one was fine. Either it fades with age or it's an infection that came from a dirty bottle. Which means I have only one more: have another one soon in the name of science, and make sure to thoroughly clean and sanitize those bottle before refilling them.

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