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I'm brewing a cross between Belgian Dark Strong and Barleywine. Currently it is it's third day. Starting gravity was ~26 Brix (~1.11 Specific Gravity). I want to push it up with candi sugar, muscovado, dry demerara sugar and caramel. I'll need almost 2kg of these for the effect I want (30 Brix).

Now, I want my yeast to ferment most malt sugars before I'll add simpler ones. There are sources suggesting that yeast may lose ability to ferment maltose if there is too much simple sugars available. But I don't want to wait for yeast to go dormant either - I'm pushing it 2 percent points above yeast strain alcohol tolerance, so I need them to be active and plentiful.

So, when should I start adding sugar? What should I look for?

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  • what target ABV are you aiming for? 30Brix could (in theory) make a very alcoholic drink that would definitely push any yeast performance envelope!
    – barking.pete
    Commented Dec 6, 2016 at 17:35
  • @barking.pete 14%, I hope. And yes. It is pushing it. I know it, guys from the yeast lab know it. After a bottle or two at the beer festival they admitted it might be within what this strain can do, but no promises. Label says 12%
    – Mołot
    Commented Dec 6, 2016 at 19:45

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As this is definitely "an experiment" (great!) I suppose one could go about it with some "scientific procedure". I agree that yeast begins to falter in very concentrated sugar solutions. There is a point (eg about 8Kg glucose in 24 litres of water) at which the strength of the sugar solution inhibits yeast metabolism. An extreme example is honey (or treacle) which is relatively stable as regards fermentation. Based on this observation one can deduce that one wants to keep the concentration of sugar in solution below a "critical level". There might be a debate at what that level may be but 4-5Kg of glucose in 24 litres is a reasonable approximation. This idea (I suppose) is the basis for the above question. The procedure I would follow would be to ferment out the natural sugars (eg maltose) in the wort then add successive batches of sugar (dissolved in in water or even wort)and check the progress of the fermentation with a hydrometer. As the SG dropped so I would be tempted to add more sugar solution until either the allocated sugar was used up or the SG did not reduce further after an addition. That would be the best/easiest way to determine if the yeast could actually cope with the additional sugar. By using such a procedure there would be at worst one dose of excess sugar in the resulting brew. So if one divided the planned 2Kg into say 5x400g batches (or even 10x200g) one could discover what the upper limit was without making a beer that could be ridiculously sweet if all 2Kg of sugar was added at once.

Yeast concentration may well play some factor in this process. One might imagine that if there was a strong body of yeast in the brew then it may be (slightly?) more active in at a higher ABV. While alcohol is produced anaerobically - growing/budding yeast needs oxygen. So aeration of the wort may be an important aspect of this process. That is usually done initially when mixing or transferring the wort. Most brewers seem not to like aerating their beer once fermentation has started. After some days some do stir up the brew to disperse precipitated yeast during a fermentation. So some action like this may be needed.

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  • Just FYI, I had a lot of fresh yeast slurry that just finished vigorous part of fermentation of bit weaker beer. About one liter of it. In that aspect I believe I'm safe. And I aerated wort pretty well. Also, I used a nutrient. Good you pointed that out, useful for future readers.
    – Mołot
    Commented Dec 7, 2016 at 15:21
  • Any link to this 8kg / 24l? I couldn't find it, and I'd really like to accept this answer, but I'm reluctant to accept unsourced information.
    – Mołot
    Commented Dec 9, 2016 at 7:19
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    The approximation of 8Kg in 24 litres come from personal observation. I wanted to make up a glucose solution to brew an "10% ABV brew" for nefarious reasons.. However I made a mistake and instead of putting 4Kg of glucose, I put 8Kg and dissolved it up. I pitched two packets of Turbo Alcotec yeast some days apart with no results. When I realised my mistake I split the liquor between two fermentation vessels and diluted the solution down. It started fermenting itself in about one hour! So while I do not consider this scientific proof - it is a good "rule of thumb" for what will ferment.
    – barking.pete
    Commented Dec 9, 2016 at 8:52
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There really is no advantage to waiting to add the sugar. Get it in there now.

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  • "the yeast will sometimes lose the ability to secrete the enzymes that allow them to ferment maltose. They will adapt themselves right out of a job!" - what about that?
    – Mołot
    Commented Dec 6, 2016 at 19:50
  • it's a theory that doesn't correspond to reality. It really doesn't work like that. I always add sugar to the boil and have no issues. Adding it now won't do any harm.
    – Denny Conn
    Commented Dec 8, 2016 at 17:05
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    @DennyConn: 'it's a theory that doesn't correspond to reality' - I have to respectfully disagree with that. I accept that it may have never had an impact in your own experience, but the repressive effects of high glucose levels on maltose metabolism and on degree of fermentation have been broadly studied and reported by brewing scientists. The bottom line is that its effects are yeast-strain dependent, and glucose levels have to be very high; so in that sense it's correct to say the effects will probably be negligible, but the theory itself is very much based in observed reality.
    – Franklin P Combs
    Commented Dec 10, 2016 at 18:26

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