Tuesday, January 22, 2008

Nutrient Additions

Did a routine punchdown yesterday. The must was 21° Brix at 72° F – the low setpoint on the temperature control.

When I went in this morning to do another punch, the temperature was still at the current low setpoint (72° F) and the sugar was down to 17° Brix.

The fermentation smells great – no suggestions of stress at this point. However since I did not add any water at the beginning of the ferment to bring the sugar down from an initial 26° Brix, the potential alcohol of this lot is over 14% and may be as high as 15%. So I want to add some nutrients at this time to make sure I don't have any fermentation problems on the back end.

It is my regular protocol to try to get all nutrient additions into the ferment before the sugar drops to 8°-10° Brix. This allows the yeast to take up the nutrients during log phase growth – at least before late log phase – when the cells have the ability to do something constructive with the nutrients. Things like making more cell mass, and membranes that are more resistant to high alcohol levels.

From the WinePod starter kit I added 8 grams of Fermaid K nutrient (18-19 g/hL) and 10 grams of diammonium phosphate (DAP, at 23 g/hL), a ready source of nitrogen. This 8 gram addition is all of the Fermaid K supplied with the kit, and is equal to about 75% of the maximum commercially legal addition rate for this product. There is no reason not to add the full legal amount – the kit should come with 10 grams of the Fermaid K nutrient.

The DAP daddition represents about 25% of the maximum commercially legal addition rate of 100g/hL. DAP is one of those things I would like to add as little of as possible – it smells and tastes awful on its own, it raises the pH of the must, and while it is really effective at building yeast cell mass when added at the right stage of fermentation, it also can push the fermentaion rate and temperature up faster than I might want. Since I got this addition in at 17° Brix I have the opportunity to make a second addition before 8° Brix if the must needs it – say if it starts to smell of sulfide, or if the lab analysis comes back showing very low starting nutrient levels in the juice.

And there's the rub – I feel like I am shooting in the dark a bit on this ferment. My timing on filling the Pod could have been better. I did it on Thursday and pulled the juice sample on Friday, but then could not get it to the lab early in the day. I refrigerated it over the weekend, and the lab was open yesterday despite the holiday. But they were unprepared for a juice sample this time of year and needed to make up fresh buffers and standards. I may get results before the fermentation is complete, or I may not. I'm relying on my backup system – a finely-tuned palate, experience and intuition.

To round out the nutrient additions I also added 10 grams of a liquid yeast extract preparation from my commercial production stash. This amount represents about half of the maximum legal addition. I like this material for its positive contrubution to mouthfeel.

After punching this addition into the must I raised the temperature control setpoints to 85° F and 90° F. I plan to make two more punchdowns today and get the ferment through its peak with these setpoints. Once the sugar gets below 2° Brix I will back the setpoints to 72° F and 75° F and complete the cuvaison at these temperatures.

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