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Yeasty, With a Chance of Sprinkles

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Beige, the color of fermentation!

Unlike a lot of other fermented products that require yeast additions, Master Vintner kits are pretty straightforward with their instructions: rip open the package and sprinkle it on top of the juice. And that's at odds with accepted wisdom from the get-go. Bread recipes want you to 'proof' the yeast in warm water. Beer recipes instruct you to make a starter, and even if you don't, they want you to rehydrate that yeast for maximum success. 

Everyone wants to get the best result out of their kit--after all, it's an investment and one that doesn't just represent sunk cost, but also your hopes for future fun and deliciousness. A lot of people want to add any extra steps they can to get the best wine possible, and rehydrate their yeast, or make a starter. 

But should you? 

The answer isn't as simple as you might think. It's absolutely true that properly rehydrating yeast gives the highest live cell counts, and the best chance to attack sugars in the fermentation medium. The key word being 'properly'. To paraphrase the package: "Add the yeast to 10 times it’s weight in water at 40­–43˚C (104­–109˚F)". 

There's a lot of stuff to consider before you do this to your yeast, from water volume, to temperature, temperature shear at addition, and sanitation. In order:

Water volume 

You're not looking at yeast in that beige powder. That stuff is a mixture of nutrients, salts, sugars, and buffers, that the yeast is suspended in, that's been dried and pelletized. Actual yeast cells are what we science types call 'really tiny'. The powder is designed so that at the correct dilution with water it will have perfect osmotic pressure for the actual yeast cells suspended within. 

Osmotic pressure in yeast is the measure of the tendency of a solution to take in water by osmosis. To de-science it a little bit, really salty or sweet things mixed with water are dense, and seek to dilute themselves into that water. If there's a permeable barrier (like a yeast cell wall), separating more/and less dense solutions, the solutions will want to pass through it. Yeast cells are designed for this action. It's how they get nutrients and water into, and waste products out of, their cells. 

C'mon, who wants to see a picture of shredded cabbage?

But consider salted meat. Or if you're a vegetarian, consider sauerkraut. When you salt a mass of cells (your beef jerky or your shredded cabbage) the salt really wants to get into those cells. they jerky will weep fluids, drying out, and the previously dry and demure cabbage will, after only a few minutes, be belching out soggy masses of cabbage juice. If you don't use enough water in the yeast rehydration process, it will be too salty, and yank water out of the yeast cells, making them into weepy jerky or soggy cabbage, but not making them into healthy yeast. 

Too much water is just as bad, as the pressure across the cell wall will cause the yeast to absorb too much water. Go back to the jerky again: soak a piece of salty beef jerky in plenty of water and it will eventually puff up like a waterlogged meatwad, lacking all structural integrity. Same with the yeast cells: if the salt concentration is too low they'll take on too much water and bust up into soggy bags of goo. 

Temperature

Nutritious, life-giving bacon. So good, and so good for you. 

A yeast cell is like a wee water balloon, the the cell machinery of the interior held in a bag made up of two layers of fatty acid esters. It might seem a little weird for a living creature to be made out of grease, but then again, here I am. 

Like all greasy things, these layers soften best in warm water. just like bacon grease in a pan: that's why you wash your dishes in hot water. If it's too cold, the layers won't allow the passage of nutrients and waste products in and out of the cell. Too hot (above 52˚C/125.6˚F) the yeast cells die of heat stroke. 

Too cold and the cells will remain stubborn little dots of grease and won't budge. You have to get it right. 

Temperature Shear

Darn you, Gilligan's Island!

It used to be thought that temperature shear was a really big deal. Moving yeast from a favorable temperature to a less favorable one too quickly was thought to reduce the numbers of viable cells instantly, ruining everything. For years I taught this fact as though it were gospel, railing against the horrors of temperature shear. 

Oopsie. Actual research shows that while it might take a short time for the yeast to sort themselves out, they do, and unless you've taken them from a viable temperature to something like boiling or sub-zero, it's not a big deal. They get right back to work when conditions improve. 

It takes me back to when I was a kid and watched a lot of TV. I was convinced that around every corner there was going to be quicksand just waiting to suck me under. Here I am today and I've only been caught in quicksand twice. 

Sanitation

Every step is an opportunity to introduce spoilage organisms to your must. It's not really mission-critical with yeast rehydration, because most wine yeast has a fairly savage K-factor--meaning they murder competing organisms as they breed--but you need to keep everything sanitary in any case, and it's one more darn thing to clean up afterwards as well. 

The Alternative

Here's the upshot: simply dumping the yeast onto the top of the must theoretically results in lower cell counts. Empirical evidence shows this isn't the case: the yeast to know what they’re doing, and a five-gram packet of yeast has less than twelve hours lag time to visible fermentation under nominal conditions. This is perfectly acceptable, and it’s a heck of a lot simpler than going through the rehydrating process, which might not even help that much. 

The first duty of a wine is to be red--Harry Waugh, possibly paraphrasing Henri Murger

And with all the time you save, go ahead and have a nice glass of wine. 


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