Saturday, October 20, 2007

Day 8 - Rosella's

Well, fermentation is well and truly underway. The Brix reading this morning was 21.3 and the temperature of the must was 67.9° F - the yeast are well established and multiplying.

At this point in time it is important to help the yeast as much as possible. Yeast need both nitrogen based nutrients and O2 to build strong cell membranes (which for yeast is where all cell metabolism takes place). Above you can see me introducing O2 via a sparger at the end of my punch down device (the sparger is submersed in the photo, you can only see the shaft of the punchdown device). Introducing O2 can be dangerous at the wrong times since most of the "baddies" are primarily aerobic organisms (remember the post about wine microbiology?) but when a fermentation is firmly established the yeast will out-compete any "baddies" for sugar and O2, so no worries there!

The other thing yeast needs is nitrogen based nutrients (remember we discussed YANC, or Yeast Assimilable Nitrogen Content here). If yeast do not have enough nitrogen they will start to break down amino acids such as cystine to acquire the nitrogen. This digestion releases sulfur which reacts with acid to form H2S (hydrogen sulfide - rotten egg smell). So every morning before punch downs start we smell the fermentations to see if we can pick up any "fartiness" (no better term for it really) and decide to add any nutrients and/or O2 to help our yeast out.

For nutrients we have two options which we often use in combo. One is called "superfood" which is like a "protein shake" for yeast, full of all sorts of amino acids, vitamins, minerals that a growing yeast needs. The other is "DAP" (diammonnium phosphate) which I like to call "yeast crack". Since yeast needs to convert any nitrogen-based nutrient into ammonia before metabolizing it, DAP just gives them a double dose straight into their system.

Happy yeast who are ready to work overtime!!

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