It's happened to all of us at least once...
It's been weeks since brewing your favourite IPA and you finally get to taste the finished product! Only instead of your tongue tingling in response to the bounty of fresh hops you generously added throughout, it is hit with an unexpected sugary profile that leaves you completely deflated.
It's hard to console someone with this fate but there are a few things you can check to prevent it from happening again...
1) Check your mash temperature: Mash temps between 148F - 160F are required for starch conversion, however at the higher end of that range, fewer fermentable sugars are being created for your yeast to convert into CO2 and alcohol. This means your beer will be home to an unintentional residual sweetness from the non-fermentable sugars left behind.
Try reducing your mash temperature to between 148F - 150F as this will assist in creating more fermentable sugars, leaving less sweetness behind to wreck your brew.
2) Review the Crystal Malts (aka Caramel Malts) in your recipe: I am guilty of it too...I love crystal malts because they can add moderate sweetness and warm up the colour of my finished beer. Unfortunately, because the sugars in crystal malts are carmelized and unfermentable, limited amounts should be used to avoid an overly sweet beer.
Consider keeping your crystal malt additions to only 5% of your total grain bill (although more is ok, it's highly recommended to not exceed 10%).
3) Review your fermentation: Unless you are counting yeast cells prior to pitching, you are at the mercy of the yeast manufacturers guidance on the viability of your yeast and the distributors ability to keep your yeast in idea conditions. Because of this, your fermentation may get "stuck" or not fully attenuate the beer, leaving that unwanted syrupy sweetness.
Take the time to check your gravity (don't assume fermentation is complete) with a hydrometer to ensure you've hit your target. If your beer has a ways to go, consider using a yeast nutrient, yeast starter or a better yeast strain the next time.
For a stuck fermentation, a yeast starter can be used to help restart fermentation. That said, do not add yeast or nutrients directly to the beer at this point...alcohol is toxic to yeast and without additional O2 (which isn't suggested at this point in your brew) your yeast cannot grow.