Day 14 - Rosella's

On Day 14 we determined that the Rosella's bins had finished their fermentations and it was time to prepare to drain and press.

Above I have graphed the fermentation so you can see basically how it ran. The left axis is temperature in °F and the right axis is ° Brix (the units we measure sugar content of the must in). You can see from both the temperature and Brix readings, the fermentation really took off around Day 6 and peaked on Day 10 which is how we want a fermentation to run at Kosta Browne. 86°F peak temperature is perfect - if the temperature goes into the mid 90's, you risk the yeast being killed off and being left with a "stuck" fermentation (where you have sugar left in the must but no viable yeast to digest it - basically a nasty bacteria's wet dream!) and if temperature is too cool, in the 70's say, you don't get full tannin and color extraction. Can't ask for anything more than one in the mid 80's which we hit.

Remember, we added the DAP and Superfood on Day 8, which was a great call - just what the yeast needed to get the fermentation in our sweet zone.

A pretty textbook fermentation really, if I do say so myself!

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!!

Day 6 - Rosella's

It is now 36 hours since we inoculated the Rosella's and we have done two punchdowns since then. At this stage punching the cap down is to mainly help the yeast colonies that might be forming in certain parts of the must (winemaker term for fermenting juice and skins) mix throughout the rest of the must. Punching down also integrates a bit of 0₂ which the yeast need to multiply.

Every day we take Brix and Temperature readings which help us understand how fast or slow the fermentation is going and whether it needs any help. Today's readings show that Brix (approx. measurement of sugar content in the must) was 25.4 and temperature was 59° F - basically where we were when we inoculated 36 hours ago. When you are punching down you kind of know how the fermentation is running (cap feels hot, CO₂ escapes when you break through the cap etc) but the numbers give us a more accurate guide and back up our sensorial judgement.

We should see some activity by Day 7 as the yeast colonies grow and start to get chomping!

I love punchies!

Once fermentation is underway, we punch down the cap twice a day. Our little friends, Saccharomyces cerevisiae, are chomping away on grape sugars and turning it into ethanol, CO₂ and heat. The CO₂ that is released pushes the grape skins to the surface and the heat "bakes" the skins into a soft cake that we call the cap. Above you can see that half the tank is punched (look at all that creamy goodness bubbling up - thats CO₂ coming up) and the other half is still caked.

The problem with a cap is that the skins are where all the flavor, color and tannins are so we need to push the skins back under the juice occasionally. It also has the effect of helping the fermentation lose some excess heat which it especially important in these wooden tanks since the staves hold their temperature well. At Kosta Browne we punch down twice a day during fermentation.

I love doing punch downs. The smells and the exercise remind you that wine is a living thing and keeps you close to the wild side of nature. Because at the end of the day, wine is just rotten grapes!