stilly_bugger wrote:
BCarter, when would you add the DAP during a Tomato Paste Wash ferment?
No worries! Sorry, should have clarified that one.
It's pretty easy really. You add it, when you detect H2S on the nose. It should clear up pretty quickly, dependent on the ferment (type, volume, yeast, ferment rate etc).
The trick is, knowing when H2S is being produced. It can quite often smell like a normal ferment. We usually add it if we have an inkling of H2S, purely due to the minor lag phase, to ensure the H2S won't get any worse...
By mid-ferment, I meant somewhere after ferment had started...if you don't detect signs of yeast struggling (H2S production), then you won't need to add DAP. You can add DAP before ferment has begun, to minimize your lag phase of beginning fermentation, but this is a minor effect. If you add at the beginning of fermentation, it's usually because you know there will be H2S problems mid ferment.
There's a few important things to remember...if you perceive H2S from the ferment, but it's fermenting quite quickly...don't add DAP...it's what we call 'stress by population'...that amount of H2S will blow off towards the end of ferment, as the yeast consume the sulphides for amino acid production.
Which brings me to the next point...if the ferment is slowing towards the end of ferment, as long as H2S isn't being produced, you won't need to add DAP...just find a way to warm the ferment to get it dry...this may be a problem for distillers...residual nitrogen in the ferment after it is dry is inviting to spoilage organisms, which may produce acetaldehyde. If there is a lag time between end of ferment and distillation for low wines, you'll get slow degradation of quality of the wash for distillation.
In short:
Yeast producing H2S --> Slowing of Ferment --> Lack of CO2 protecting ferment --> Ethyl Acetate and Acetic Acid production from Oxidised Ethanol and Spoilage
(Ethyl Acetate and Acetic Acid degrading of Ethanol share in wash. H2S, causing larger heads portion).
and
Residual Nitrogen Post Ferment --> High Nitrogen, Low Sugar, High Micronutrients from Yeast Hulls --> Bacterial Growth --> Acetaldehyde and Diacetyl Production.
(Acetaldehyde and Diacetyl real pains to separate, as detection threshold is very low).
The aim of our game is separation of alcohol...these steps (although being fine details), aid in maximising the ethanol separated in distillation, and the ease at which high % v/v can be extracted.