Attenuation Concerns

I have used yeast rated at 70-75% attenuation for my last 3 beers; all 3 have finished with only 65% attenuation. 1 was with dry yeast and 2 were with liquid yeast (for which I made 1qt starters). I have fermented all 3 within the temp ranges for the yeast. I aerated all 3 by shaking the carboy for 5 minutes.

Anyone have any ideas as to what the issue might be?

Should I be concerned about the low attenuation or RDWHAHB since I'm getting to at least 65%?

I have had the exact opposite problem- OVER attenuation and some of my beers were finishing at 1.007 or so.

Are you doing AG or PM or extract? For AG, I think mashing temperature and time make a huge difference and I've adjusted that. For extract, the only thing I can think of is that your extract is less fermentable than it should be and maybe look at the brand and see if using the same brand is the issue.

I wouldn't worry much about 65% attenuation, except for one thing- if you bottle, how do you know with 100% certainty that the beer will never start up again? That would be the only concern I have. If you keg, no worries!

There are a few reasons why this could be. Yoops hit on the majority. One thing though, you say you fermented in the temperature range, but were you in the high part or close to the lowest part? Remember that cooler temperature slows yeast activity, although I still don't think that would push you getting below 70% at least.

A couple thoughts. It has been mentioned that Laaglander (sp?) malt extract is notorious for having a high percentage of malt that doesn't ferment. Also, you might want to try a different method of aeration just to see. The method I use, which wouldn't cost you much to try is to take one of those aluminum 'tomato strainer' colanders (the kind that usually comes with a steel frame base and a big wooden Pestle). Each hole acts like a tiny jet for the wort, and I have never had ferment problems as a result of inadequate aeration using this technique. If you are doing AG, try and mash a batch @ 148°F and see what you get (don't forget mashout).

Yooper mentions a good factor if you are AG (also look at mash ratio). Other factors I would look at are the any non-fermentable content of your recipes, alcohol tolerance of the yeast strain, how you are measuring the temp during fermentation & yeast viability (which you wouldn't necess expect given the different yeast used).

Thanks for the input gang.

These were all extract batches (no time in the summer for PM) using the exact same extract - Munton's Extra Light DME - so maybe that is the issue.

Fermentation temps were smack in the middle of the temp ranges for each yeast, maybe I'll try fermenting a little warmer next time too.

I do keg so bottle bombs is not my main concern, just trying to improve my brewing skills each and every time.

not all sugar is fermentable. unfermentable sugars lend sweetness and/or body to the finished beer.