My first crush - UPDATE

The yeast have completed their work!
An update on my post from 9/25/14

So far, the Malbec fermentation is proceeding like clockwork (knock on wood!). In a little under two weeks (at the beginning of last week), the Brix were down to 0º, meaning that all the sugar had been consumed.*

The process of fermentation is not just about turning sugar into alcohol. Yeast do other stuff as well, including the creation and transformation of important aroma molecules (that’s “secondary aroma,” for those of you who came our Aromas workshop last week). And-- in red wine-- the juice, the yeast, and the alcohol they produce all interact with the solids they’re soaking with, extracting tannins, pigments, and other good stuff from the seeds, stems, and grape skins. The color change that took place in the must over those two weeks was astounding.


I had just started celebrating the fact that we no longer needed to worry about making everything around us sticky with grape juice during our wine processing, only to realize that instead we now needed to worry about staining everything red with wine.


Of course, we tasted the wine, too. I was very impressed—it tasted like wine, and it tasted good! But it’s also a completely different animal from what you would normally purchase as wine. There’s still a kind of wild and fruity fresh purple grape character to it, as well as a bright acidity uncommon in red wines—I imagine it’s normal to mature out of those things after a while, but I think I’ll miss it when it does. I think I understand now why people drink Beaujolais Nouveau.

Most importantly, the wine had no microbial off flavors—nothing funky, moldy, or vinegary. So far, so good.


Now that fermentation was finished, the next step was to press. This process separates the juice from the solids, squeezing on the solids to do so. For this, we rented a bladder press from MoreWine. This contraption works as follows:

1. Pour the grape must in the top, into a space that is walled by a cylinder of mesh.

2. Before any pressing occurs at all, a large volume of wine will pour out the mesh and into the collection moat, and from there flow into whatever container is waiting below the press. The solids will stay in the mesh. This liquid is called the “free run” wine, and, as I understand it, is often considered the best part.
There is still quite a lot of liquid tied up with the solids in the berries, and that needs to be pressed out. In the center of the cylinder is a rubber bladder for that purpose.

4. Put a lid on the press and turn on the water input from below. The water fills the bladder in the center of the press (but doesn’t come into contact with the wine itself). The bladder expands, pressing the grape solids against the sides of the mesh and squeezing the remaining juice out of them, into the collection moat below. This is called the “press run.”

5. Monitor the pressure being exerted on the grapes using the gauge under the press. The more pressure is exerted, the more funky stuff comes out of the grape skins and seeds, including tannins and other compounds that might lead to off flavors. On the other hand, a little of these compounds can add some desirable structure and body to what might otherwise be a one-dimensional wine.

The advice given is to taste the wine constantly as the pressure increases and to stop pressing as soon as the wine starts tasting “thin” or “harsh.” And in fact we didn’t find that the wine tasted unpleasant at any time during the pressing, so we continued to the upper limit of the bladder press, with is 3 bar.


From an estimated 37.5 gallons of grape must, we ended up with something slightly less than 30 gallons, about 2/3 of it free-run and 1/3 press-run. We divided the wine among 5 carboys and filled the carboys up to just a couple of inches from the top, in order to minimize oxygen exposure. Both chemical oxidation and the activity of oxygen-breathing bacteria can cause problems during wine aging.


Pressing wine does not involve filtering it, so two days later (also like clockwork), a lot of the fine solid grape gunk and also dead yeast cells—that is, the gross lees—had settled out of the wine and accumulated on the bottom of the carboys. These lees can contribute off flavors to the wine if allowed to stay there. So it was time to rack.

We had a sterile siphon and, luckily, and extra carboy, so it was fairly simple to transfer wine from one carboy to the next and leave the lees behind. It was less simple to figure out just how much to transfer and how much to toss out. On the one hand, this is hard-won wine and it hurts to throw any of it out, but on the other hand we didn’t want to risk ending up with an entire carboy of wine that tasted less than perfect because of too much lees contact. So we ended up losing about a half-gallon of wine+lees per carboy. I imagine this is one place where some personal experience will come in handy, over the years.

Our winemaking handbook also advised that we use the transfer as an opportunity to aerate the wine—but running it down the side of the carboy to maximize surface area exposed to oxygen. Apparently aeration during the initial racking is a good thing, to jump-start the aging process. And yet we’re supposed to minimize oxygen contact as the wine sits. This is yet another place where I’m sure experience and judgment are at play. I do a lot of work culturing both aerobic and anaerobic bacteria in the lab, so you’d think I’d have better intuition about when oxygen is a good thing for biochemistry and when it’s not...

Malolactic fermentation

As I mentioned earlier, our wine has a lively acidity. Much of this comes from malic acid, an acid that is found in many fruits and also gets added to many sour candies to give them a satisfying juicy-puckery quality. “Juicy-puckery” is an effect you might sometimes go for in some white wines, but almost never in reds. Apparently almost all red wines are put through malolactic fermentation.

There are bacteria that derive energy from turning malic acid into lactic acid.** In doing so, they remove one of the acidic groups from the malic acid and release it as CO2, taking the acid from diprotic (2 acidic groups) to monoprotic (1 acidic group). The resulting lactic acid has a “softer” character—we perceive it as less bitingly acidic. Lactic acid is the kind of acid you find in yogurt, as well as many other bacterially fermented foods (sauerkraut, sourdough, etc).

The bacterial species used for malolactic fermentation is almost always Oenococcus oeni (get it? “oeno” is the Greek root for “wine”). I’m sure O. oeni often takes up residence in wine fermentations spontaneously and it was probably originally their idea, not ours, to do the whole malic-to-lactic transformation. We like the idea so much that we purchased some bacterial culture to add to our wine.

The process of adding O. oeni to our wine was similar to the process of adding yeast. We hydrated the bacterial culture in water with some added nutrients for about 15 minutes before distributing it among the carboys. We also added extra nutrients to keep the bacteria going—something called Opti’Malo Plus, which, according to the MSDS, is 100% dead yeast. I am frankly impressed at the number of different ways that dead yeast can be processed and packaged for use as a nutrient aid in the various stages of winemaking.

Malolactic fermentation should take a few weeks to carry out. During this time, we’ll test the acid levels periodically, and stir the lees regularly to make sure the microbes and the nutrients can come into contact. Every time we do, we’ll gas the headspace of the carboys with argon to keep the oxygen out. (This is something we didn’t have to do during fermentation because the yeast produced prodigious amounts of CO2 themselves.)


The flavor imparted by oak wood is one that’s commonly expected in Malbec wines, and certainly one my dad wanted. Of course, that flavor traditionally comes from aging wine in an oak barrel. But traditional oak barrels hold ~60 gallons or more and we had less than 30, and if you can’t fill a barrel full, all the air filling up the empty space can cause serious problems with oxidation. There’s that, and the fact that a typical wine barrel costs several hundred dollars and takes up an awful lot of garage space.

Happily, you can buy oak chips to put in your wine, so that’s what we did—a few grams of American oak per carboy. Apparently these chips also provide a happy home for the malolactic bacteria! We don’t get to choose toast level, age, and all the other nerdy details that go into oak; nor is aging in a plastic carboy quite the same chemical environment as in a wooden barrel. But we do what we can.


So, we wait patiently (but not without a little anxiety) for a few more weeks until malolactic fermentation is finished, before the next step: racking again and aging.


* I should note that this Brix measurement was not straightforward. As you’ll recall, a refractometer works because dissolved sugar affects the refractive index of water in a predictable way, so if you can measure the refractive index of a pure sugar solution, you can figure out how much sugar it contains. However, ethanol also affects the refractive index of a solution. So if your solution contains both an unknown concentration of sugar AND an unknown concentration of ethanol (as wine does, once fermentation has begun), the calculation is more complicated. The saving grace is that we know that all the ethanol must have come originally from sugar: the higher the ethanol, the lower the sugar, and if you know the starting concentration of sugar, that’s a quantifiable relationship. So you can use a combination of this relationship plus the refractometer measurement and also your knowledge of how sugar and ethanol each contribute to the refractive index, and from all that you can derive the sugar concentration.
But you don’t have to do the calculation yourself. MoreWine provides an Excel spreadsheet that will do it for you. Of course, it only works if you know how much sugar you started with.


** Biochemists might be interested in this note, which I found in the MoreWine manual:
“Note: Because CO2 is produced during the process, the conversion of malic to lactic acid is commonly referred to as “fermentation”. However, an MLF is not a true fermentation because no alcohol is being produced from the metabolism of sugars. Despite this technicality, Malolactic Fermentation, or MLF, is still the accepted term.”

As a microbiologist, my first thought was: wait! A process certainly doesn’t have to produce alcohol in order to be called fermentation. I mean, if we’re going to get “technical,” then we should use the biochemical definition of fermentation, which is: “An ATP-generating process in which organic compounds act as both donors and acceptors of electrons” (Berg 2002). [Though a quick search online revealed that there are a LOT of different definitions of “fermentation” floating around out there...] “ATP-generating” means “energy-generating.” For example, in lactic acid fermentation, energy is generated by turning glucose into lactic acid—it’s what bacteria do in making yogurt, and what your muscle cells do when they’re not supplied with oxygen fast enough. It doesn’t involve ethanol but it most certainly is a kind of fermentation, without a doubt.
However, producing lactic acid from malic acid is a different process, and I think actually the MoreWine manual is correct that the malolactic transformation is not a fermentation (even if they’re incorrect about the reason). It’s actually a decarboxylation (removal of CO2 from lactic acid); energy is generated by trading lactate for malate across the plasma membrane, thereby creating a proton gradient that can be harnessed to create ATP (Poolman 1991).

Some Resources

Berg, Jeremy M., John L. Tymoczko, Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, and Lubert Stryer. 2002. Biochemistry. 5th ed. W H Freeman.

MoreWine! manuals and instructions page

Poolman, B., D. Molenaar, E. J. Smid, T. Ubbink, T. Abee, P. P. Renault, and W. N. Konings. 1991. “Malolactic Fermentation: Electrogenic Malate Uptake and Malate/lactate Antiport Generate Metabolic Energy.” Journal of Bacteriology 173 (19): 6030–37.


Once again, thanks to my dad, K. Mark Lee, for the photos included in this post.