Too sweet?

My last IPA came out a little sweet. My assumption is that I didn't ferment enough of the sugars away. I had an attenuation rate of 70% when the yeast said it should go 75%.

First of all, is my assumption correct?

Second, how do I rectify this in subsequent batches? Use a starter? How do I get a really high attenuation rate from my yeast?

some more info:
OG was 1060, FG was 1018. Primary 10 days, secondary 40 days, bottle 10 days. Fermentation temps ranged from 75-90 (I don't have AC)

 

Using a starter could help.

Making sure the temperature stays pretty constant is good. Also, I tend to like to ferment near the top range of the yeast (never above 70 degrees, but 68 or 69). The (slightly) warmer temperature means slightly more active yeast.

The other thing you could do is really let the fermentation go for more time.

 

Was this an extract recipe? Sometimes certain extracts have more unfermentable sugars in them

 

Perhaps...there are a number of variables that effect attenuation, starting with your recipe and ingredients to yeast strain, fermentation conditions, ect. More detail required.

 

I agree with brewt00l with the variables. If your actual temp range did hit 90 that would blow out the yeast quickly. Ale yeast obviously can take higher temp, but I have never taken them to 90. 1018 does sounds like a sweet end product though.
On another note:
I am cheap and don't run the AC either, but I brew lagers even through the summer. I keep the carboys cool in a marine chest in the bathtub, which I fill with water and add frozen 2 litre bottle that keep the lager yeast happy for weeks around 48-53 deg. I know this won't help your current situation, but for future projects you might consider it. This is not a novel idea as I have seen other do similar things.

 

Here's the recipe:

9.15 lbs Gold Malt Syrup extract
1 lb Briess Caramel 40 for steeping
1 oz Centennial hops for bitterness
1 oz Centennial hops flavor
2 oz Centennial hops for aroma
Wyeast #1084, Irish Ale yeast
1 oz Centennial hops for the dry hop

I pitched at around 68 degrees.

 

I would think that a FG of 18 is a bit high , there are more than likely unfermentables that made it sweet. Aslo a 40 day secondary seems really long for an IPA, that gives the hops a lot of time to mellow out. I am of the opinion that IPA's are best when served fresh and benefit from just a week our two, at most, in the secondary, just for dry hopping and clarification.

Cheers