Yeast/Green Apple Taste

Question

I have homebrewed with family many times and never had problems, nor did I with my first batch on my own. The last couple, however, have had a yeasty/cidery/apple odor. Very strong. I doubt it is contamination; I am very careful about that. I must have introduced some systematic error in my brewing. The beers:

• Strong Ale something like an Arrogant Bastard. I can post a link to the recipe on brewersfriend.com if needed. It hit the FG exactly, but smelled extremely strong. 4 weeks in primary, well temp controlled. 68 for first two weeks, 70 for second two, and due to a loss of power (apartment flooded) high 70's for the last two weeks. I decided to bottle the stuff and age it anyway. In hindsight I probably should have left it on the yeast? After aging 3 weeks, the smell is not as strong and the taste is correct.

• Hazelnut Brown ale. 68 for first week, 70 for a few days, 72 for a few days. All activity in blow-off stopped after 11 days, at 14 opened to see if ready for bottling, but it has a fair amount of yeast/apple/cider smell. I threw the lid back on and have it aging in the mid 70's. The FG is still a little high, but only be a few thousandths. I assume this one is just not done?

Other notes, I used starters for both and made sure to pitch a lot of yeast. Wyeast 1056 for the first, and a mixture of White Labs English and European Ale yeast (WLP002 and WLP011 I think) for the latter. The fermentation was extremely vigorous on the second day of each, to the point where I have to use a quick disconnect tube fitting to keep the blow-off tube on. Blew tons of krausen and beer out the top.

Should I continue to age the two? And what do you think is causing this so that I can avoid it?

Thanks! Sorry for the wall-o-text.

Edit: The smell has a slight cider smell to it, but it smells mostly like a fresh vial of liquid yeast. But very, very strong in the AB clone. Maybe a bit of apple. My best idea is that I stressed the yeast and it did not finish the conversion of the acetylaldehyde into ethanol. As far as sanitation, I have a second primary bucket, which I fill with water and iodine solution. Usually I put in a bit more than is needed. All utensils stay in that unless in use. I apply the solution to the primary and the pot I use (I have to do extract for the next couple months until I move into a house). I usually leave a bit on there. I also have a squirt bottle I fill with the stuff to make sure things are sanitized. Some items which are hard to get water into such as a bottling spicket, I will soak, then pout throught he dishwasher's sanitize cycle, then soak again. I am thinking from now on to use StarSan and sanitize all surfaces in my kitchen as well, including outside of all vessels. I am brewing today and that is my plan so far.

Answer 1

The yeast odour can really only come from yeast. After 10-14 days in primary, be sure to leave the carboy to cold condition until the yeast have settled out and the wort looks fairly clear.

The apple/cidery flavour does sound like acetaldehyde, which can come from to short conditioning period, oxidation, or contamination by acetic acid bacteria. The cider-like flavor is probably both from a combination of the apple aromas plus the sharpness of acetic acid. Review your sanitation procedures - e.g. use StarSan rather than iodine.

From homebrewtalk wiki

Causes of acetaldehyde

Acetaldehyde is an compound formed by an intermediate step in the conversion of sugar to ethanol by yeast. Under ordinary circumstances, any acetaldehyde formed during fermentation will eventually be taken up and converted by the yeast. The most common cause is removing the beer from the yeast too early, before the yeast has a chance to complete fermentation. In finished beer, the ethanol reaction can sometimes be reversed by oxidation, resulting in acetaldehyde re-formation. Adetaldehyde is also a byproduct of the conversion of ethanol to acetic acid (vinegar) by acetic acid bacteria. If this is the cause of your acetaldehyde problems, it will probably be accompanied by a vinegar-like or cidery flavour and aroma.

Answer 2

Green apple aroma is typical of acetaldehyde. It could be the result of oxidation late in the fermentation or when bottling. Leaving it on the yeast helps, as it will reduce some or all of the acetaldehyde to ethanol.

References: Pico Brewery, BJCP, BYO