Stressed yeast causing off flavor?

[BMWMK2]

Ive made a few extract batches, all LME, and they all had a bitter twang to them. I just asumed that it was the dreded "LME twang". And ways just poured my wort into the fermentor to aerate. I recently made my first all grain batch, AHS lawnmower lager, did the same thing to aerate. All of my batches took a little longer to get fermenting, the all grain one took almost 72 hours. Now i know that using a starter would help that but what i am asking is by pitching the liquid yeast without aerating vigorusly stress the yeast and caus the bitter flavor im having?
I recently bought a aerating kit and on my last two allgrains after areating for 20min with it the fermentation kicked off vigourously before 24 hours. These beers are not done yet so i cant taste them and compare. I even had to put a blowoff tube on the last one, i thought the lid was going to blow.

 

[SC_Ryan]

It sounds like astringency is the off flavor you are experiencing. There are multiple things that can cause astringency. In all grain brewing a hot sparge (over 170*) or over crushed grains can result in astringency. Probably not your problem because you were experiencing it before you switched over but it's something to keep in mind.

Wild yeast or oxidation is probably more likely the issue. Wild yeast can be cured with proper sanitation and oxidation could come from your bottling or racking practices. You want to make sure there is little to no splashing in your beer post fermentation. I wouldn't worry too much about "hot side" aeration.

If your astringency is coming across as an astringent bitterness on the sides and back of the tongue (kind of like sucking on a used tea bag) then your water may be your issue. Highly alkaline water can cause this flavor in lighter color beers.

I would highly recommend dialing in your pitching rates as stressed yeast can cause a number of off flavors. If you have pitch rate and fermentation temperatures down it is much easier to isolate an off flavor.

 

[BMWMK2]

im pretty good on not splashing the beer after fermentation, so i dont think its oxidation. i will have to test my water. how would i lower the alkalinity of my water?

 

[SC_Ryan]

im pretty good on not splashing the beer after fermentation, so i dont think its oxidation. i will have to test my water. how would i lower the alkalinity of my water?

You can dilute your source water with distilled water or reverse osmosis water and that will reduce your total alkalinity. You will more likely need to balance your total alkalinity by adding some calcium to the water (or the mash really). You need to know exactly what you have in your source water before you start adding and subtracting minerals and making adjustments. You don't want to fool with your water unless you really understand what your doing. Start by getting a water report from your water company and then read this.

http://www.howtobrew.com/section3/chapter15.html