Lactose, really unfermentable?

[Dave_K]

So I've read a lot about using lactose for back sweetening and that it is an unfermentable sugar, but is this really true?

The first thing having me questioning this is beer smith, among other brewing calculators. They all seem to show milk sugar(lactose) as pretty fermentable by default.

I haven't found this actually discussed on here, if it has I apologize, but what I did find is a contradictory statement on HBT's wiki pages, found here:
https://www.homebrewtalk.com/wiki/index.php/Lactose

This says lactose is "largely unfermentable" which insinuates some fermentability. However, in the same paragraph, it is says "the sugars will not be converted by yeast."

So which is it? Is lactose somewhat fermentable, and to what extent? Or is it truly unfermentable?

 

[Silentdrinker]

Beer smith has a glitch. If it's how it was as I remember, it treats it as 100% fermentible. This has been an issue for a long time and apparently still not fixed. Wine and brewer yeast can't break the lactose down enough to digest/ferment it. So it's not a fermentable sugar.

 

[The_Bishop]

Doesn't happen on my version of beersmith?

 

[Silentdrinker]

Doesn't happen on my version of beersmith?

Your version doesn't calculate lactose as a fermentable? What versions do you have? I not even sure what the current version is. I wasn't willing to buy it until he fixed the issue. I know it was a problem for a year or so. There are lots of posts about it and how it was on his list of fixes. I finally gave up checking because he didn't seem to pay it any attention.

Edit: I looked, and it appears he added a feature in ver 2.2 to allow fermentables to be checked as non fermentable, so this fixes that. Cool!

 

[chickypad]

You need to manually check the box for "unfermentable" on the grain details. It was added on one of the recent updates.

 

[Dave_K]

Thanks for the responses. I figured it was just an error in beer smith, which is why I always changed it to unfermentable, but seeing the wiki page here about lactose had me questioning it.

 

[Silentdrinker]

but seeing the wiki page here about lactose had me questioning it.

Im sure it's referencing lactose being largely un fermentable in the general sense vs brewing specific.

Wine/brewing yeast can't break it down; for us it's not fermentable. However, there are lactose fermenting yeast for other uses.

 

[FarmerTed]

Lactobacillus will ferment it, but like others said, brewer's yeast won't. I don't know if Brett does or does not ferment it.

 

[The_Bishop]

For reference, I'm on 2.2.12 of Beersmith.

 

[testingapril]

Lactobacillus will ferment it, but like others said, brewer's yeast won't. I don't know if Brett does or does not ferment it.

Some Brett will. Not sure if all Brett will.

 

[Dave_K]

Lactobacillus will ferment it, but like others said, brewer's yeast won't. I don't know if Brett does or does not ferment it.

Ahh that makes more sense now. Thanks for clearing that up!

 

[Jonkl]

Some Brett will. Not sure if all Brett will.

I grabbed the wrong bag of white powder, and ended up priming a beer I'd secondaried with Brett C (WLP645) with lactose. I can personally attest that this particular strain of Brett will not really ferment lactose.