3 of last 4 batches had bad apple taste

I cannot find a common bond between them either. First I thought it was a problem in my sanitation and it resulted from some kind of infection. I boiled everything, swapped out old tubing, etc.

By the time I open the primary for my 1st SG test I can smell the apple-ness. I would think it was the fermenter, but I did have a batch that came out great from it.

I'm really confused what is happening. Is there something I think I am doing right that I am likely doing wrong?

This would be my guess:

Acetaldehyde - Home Brewing Wiki

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.

How long is your usual primary fermentation? Do you secondary?

The beers in question primaried 9, 17 & 14 days.

I think it could be from bad malt. The batch which came out fine was a 3gallon all grain.

Are you getting a strong healthy fermentation? Underpitching or low temps could cause this.

If anything my temps are high. Been fermenting around 74.

Either I have:
Bad Malt
Infection
Odd fermentations

Oddly the batch which caused this post is mellowing in keg and tastes better now. I cracked the older ones and still awful.

is this partial mash or all grain mash? i got a lot of wierd flavors from dry malts. also, have you thought about the water you are using? i actually noticed a big difference when i went from bottled to tap water. my tap water made much cleaner tasting beer. sounds frustrating. i hope you figure it out.

One was partial mash, another was extract. I think I have to take it back to square one.