I am going to try to brew a Russian Imperial Stout with the intent to have something more along the lines of a High Gravity/Desserty type beer similar to Bells Batch 9000. I am using a kit recipe and modifying it with a little less hops, adding cocoa and vanilla bean with bourbon and american oak with lactose for body/sweetness. I am very familiar with alcoholic fermentation because I make wine for a living. I will be kegging this beer and the bourbon will be added post fermentation so no need to warn me on the cautionary ABV. I am trying to sort through all the information in my literature and through the grapevine (literally) what I hear about brewing and I am finding what I would consider mixed information on the use of lactose in beer. I understand lactose's use but I see people adding it to the wort instead of the finished beer. I would think that having a non-fermentable sugar would stress the yeast and risk an incomplete or stinky fermentation. Is lactose normally added before or after fermentation and why? Also, any good videos on all-grain brewing?

1 Answer 1


IMO there is no need for Lactose in a RIS to start with. The base recipe will bring plenty of body and residual sugars to the the final product.

Lactose doesn't have an appreciable detriment on the yeast during fermentation either. I have never had a beer suffer because lactose was in the ferment. It doesn't slow the yeast down any, nor is there and "stinky" fermentation or poor fermentation. I have always added it in the kettle. Adding later you'd need to dissolve it in some water first and then you'd be diluting your beer some when you finally add it.

Lastly, a pound of lactose in a 5-6gallon batch is the norm.

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    Agree with everything but the "no need for Lactose in a RIS." One of my favorite homebrews is a RIS I have on tap now - with 1.33 lb of lactose in it. It's not needed for body, but as a sweet dessert beer it's great. And +1 on the explanation for why it's added in the boil - it just makes life easier.
    – Brandon
    Dec 15, 2010 at 3:19
  • I was thinking more traditionally RIS doesn't employ lactose in it. I get plenty of residual sweetness out of a heavy hand with specialty malts normally. But sweetening it up with lactose for a different effect (like dessert beer) is perfectly legit, just not the stylistic norm. That was my point.
    – brewchez
    Dec 15, 2010 at 15:58
  • Since many RIS can suffer from under attenuation and heavy use of crystal malts, I would suggest adding the lactose after fermentation. This way you can control the amount of body the final beer has. Dec 15, 2010 at 17:09
  • But underattenuation is a subjective term when brewing big beers like RIS. You wouldn't expect a >70% attenuation. A characteristic of this beer is to finish in the 1.030s, even on the high side of that like 1.036-1.038. Using crystal malts and the heavy amount of roast will get your there, even with an exteneded rest at a lower mash temp. The results of which would still be plenty of body and a pleasant residual sweetness.
    – brewchez
    Dec 16, 2010 at 13:17

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