Stepped starters and to decant or not decant

[DocAnna]

A question for those far more experienced in such things.

So I've two 1.75 litre starters merrily foaming and multiplying my diamond lager yeast. I plan to step this up to two 3 litre starters, the question is to decant or not:
Option
1: Do as the stepped starter instructions tend to say - chill, decant, top up with fresh wort - 90 - 100g DME per litre ie chill overnight, decant off the used supernatant and add fresh wort with about 300g DME in 3 litres each to reach about 3.25 litres (3 litres new wort + 0.25 litre of yeast)
OR
2: Why if I'm stepping up the volume do I need to bother with chill and decant? Instead avoid the risk of cell loss with cool and warm, dissolve the same amount of DME required in 1.5 litres of water and add that to reach the same final DME concentration and volume of 3.25 litres.

Option 2 seems faster, same sugars concentration and avoid the chill and decant in the middle? What am I missing here?

Anna

 

[PhilBrew]

Hi Anna

Option 2 seems faster, same sugars concentration and avoid the chill and decant in the middle? What am I missing here?

... it may be that you're using the same concentration of sugars, at each stage, but it's the total amount of food available (the sugars available to be consumed by the yeast) that really drives the size of population that they'll reproduce to ... there are ways to speed up your cycle of stepped starters (that don't involve chilling and decanting), but you'd need to consider option 3 to get you a similar cell count as option 1 ...

3: Prepare 2x3 litres of fresh wort, with about 300g DME in each ... and pitch (all of) your 1.75 litre starters into these when they're at "high krausen" (basically when you would otherwise have started chilling them), giving you two 4.75 litres starters

Cheers, PhilB

 

[DocAnna]

Hi Anna
... it may be that you're using the same concentration of sugars, at each stage, but it's the total amount of food available (the sugars available to be consumed by the yeast) that really drives the size of population that they'll reproduce to ... there are ways to speed up your cycle of stepped starters (that don't involve chilling and decanting), but you'd need to consider option 3 to get you a similar cell count as option 1 ...

3: Prepare 2x3 litres of fresh wort, with about 300g DME in each ... and pitch (all of) your 1.75 litre starters into these when they're at "high krausen" (basically when you would otherwise have started chilling them), giving you two 4.75 litres starters

Cheers, PhilB

Thanks Phil, I guess I was showing that options 1, 2 and your option 3 all have the same total amount of food. The advantage of 2 is that I only need to boil 3 litres total to divide between the two - the amount of DME would be the same as if I was boiling 3 litres so it will have a higher SG but when diluted by the existing starter the FG would be the same as if I'd decanted and boiled 3 litres. I was just worried there would be something unknown in the spent starter that would slow the second stage starter.

If I had the time I'd do one option 1 and one option 2 but I have to leave for work at 7:30 on Thursday and won't be back till midnight, which makes transferring the starter that day a bit difficult.

Anna

 

[PhilBrew]

Hi Anna

I was showing that options 1, 2 and your option 3 all have the same total amount of food.

... aaah, I see where you're going with this now, when you said "dissolve the same amount of DME" in option 2, I was thinking you meant the 90-100g per litre bit, not the 300g total ... but now I understand what you mean, I'm afraid it's still a No IMHO, I don't think that option 2 is a good idea.

You've not said how long you've had the first starter going for ... if it's just at high krausen now and you would (under option 1) chill and decant this before pitching just the yeast, then only 10-20% of the sugars in that wort might have been fermented (the yeast have been too busy reproducing to get around to eating ) so when you mix with your concentrated top-up wort (under option 2) you may actually be creating a starter at around 1.055-65 (or higher), which isn't the greatest environment for yeast cells to get on with multiplying (which is the purpose of a starter) ... if instead, the starter has been going for a few days and it's likely to have fermented out fully, then you might well be OK, but then you'd probably find that the yeast would be settling at the bottom of its own accord and I'm not sure why you would feel the need to chill before decanting

Cheers, PhilB

 

[DocAnna]

You've not said how long you've had the first starter going for, if it's just at high krausen now and you would (under option 1) chill and decant this before pitching just the yeast, then only 10-20% of the sugars in that wort might have been fermented (the yeast have been too busy reproducing to get around to eating ) so when you mix with your concentrated top-up wort (under option 2) you may actually be creating a starter at around 1.055-65 (or higher), which isn't the greatest environment for yeast cells to get on with multiplying (which is the purpose of a starter) ... if the starter been going for a few days and it's likely to have fermented out fully, then you might well be OK, but then you'd probably find that the yeast would be settling at the bottom of its own accord and I'm not sure why you would feel the need to chill before decanting

Ah so that's exactly the kind of insight I was hoping for - thanks I really hadn't thought of that! I'm fermenting after rehydration with go-ferm protect so that keeps the krausen right down to almost nothing through its surfactant effect but also means it eats up the sugars fast - it's been 28 hours since I put the starter on and if left for an hour it's already starting to clear into 3 layers.
Thanks for the advice, I think I'll go with the decant and fresh wort option as you suggest, though to cut down on the boil then cool time, think I'll boil the DME in a smaller amount of water and top up with plain boiled water for the full volume.

Anna