How can I increase the viscosity of a Russian imperial stout?

I've heard of making boils longer Use oats, What do you recommend?

Thank you so much!

Regards, Erik Dobrychtop. Cya o/

3 Answers 3


Oats, long boil, higher mash temp, Cara malts, protein rest, and unconverted starches when applied properly will aid to give that thick body and viscous mouth feel.

The mouthfeel comes from medium-sized proteins and unfermentable sugars (dextrins) usually.

RIS can utilize a lot of unfermented sugar, since the style allows for a lot of hops that can be used to balance the sweetness.

  • 2
    Use a yeast with lower attenuation too.
    – chthon
    Commented Jun 26, 2017 at 8:00

A higher mash temperature would always be my first port of call, push it up to 69-71 C.

After that yes oats can help, but you have to be wary of stuck mashes.

Longer boils will thicken the final product by concentrating sugars, proteins etc...

My recommendation would be to alter only one variable at a time and to start with a higher mash temp, next I would change the malt grist, then I would add oats.

Finally I would lengthen the boil.

  • 1
    If your pH is correct, then a longer boil would only drop out more proteins from the wort, so no increase in body there.
    – chthon
    Commented Jun 26, 2017 at 8:00
  • 1
    Not so, it would reduce the overall volume through evaporation, therefore making the non-fermentable sugars more concentrated, thus raising the viscosity. And will concentrate soluble proteins/amino acids/fats etc... But the main effect should be from concentrating the non-fermentable poly saccharides.
    – Mr_road
    Commented Jun 28, 2017 at 21:12
  • Yes, more body through non-fermentable sugars, but not more body through proteins.
    – chthon
    Commented Jun 29, 2017 at 7:04

I didn't see grain crush size mentioned here...

Check out this exBeeriment: http://brulosophy.com/2015/11/23/mind-the-gap-course-vs-fine-crush-exbeeriment-results/

He actually made a stout with this, and stated:

When presented these beers in a quasi-blind triangle, I was consistently able to distinguish them. I perceived the fine crush beer as having a fuller mouthfeel, greater complexity, and subtle alcohol twang in the finish. While my preference leaned toward the fine crush beer, the coarse crush sample certainly wasn’t bad! I experienced it as possessing a stronger roast character that was somewhat sharp and quite pleasant, although it came across much thinner than the fine crush beer and had qualities more consistent with Robust Porter than Russian Imperial Stout.

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