D’oh! Lysozyme…

So, my 2011 Suisun Valley Montepulciano has not gone through malolactic fermentation despite two separate inoculations and the addition of Leukofood.

The cellar temperature has been above 70°F for some time and the pH is 3.4 (and change), so temperature and pH are not the reasons why the wine did not go through MLF.

Yesterday, while doing some blending trials of my rose vodka experiment with my friend Jeff Miller, I checked malic acid levels and pH and there still was no progress, so I pitched some bacteria from a new batch.

On my way up from the cellar it finally clicked: Because the fruit had not looked very clean, I had added lysozyme to the must.

D’oh [from Simpsons Wiki]

No wonder I could not get malolactic fermentation going. I can’t believe I forgot about this, but I’m glad I do keep records which I could check and verify that I made this addition.

Lysozyme is a commercially-available enzyme, derived from egg whites, and is used to inhibit malolactic bacteria. There are likely a number of variants and sources of lysozymes in nature. They all do the same thing: they kill certain bacteria by breaking down their outer cell walls.

Lysozyme is also reported to be helpful in a couple of other ways: It has been reported to be effective in preventing volatile acidity formation in stuck or slow ferments. Additionally, lysozyme activity has been shown to control some fungi (  1 ,  2  ), and adding it to unfermented must contaminated by mildew or mold can stave off unwanted organoleptic characteristics in the finished wine.

Now, lysozyme – a protein – eventually precipitates out of the wine and settles in the lees. By a mechanism similar to tannin reduction with egg whites, lysozyme is bound to tannins and falls out of solution. Once the wine is racked off the lees, MLF is more likely to occur (more here). This is expected to be particularly true of red wines.

It would stand to reason that about 9 or 10 months after crush, lysozyme activity should be low enough to allow malolactic conversion to take place.

Yet, that is not happening.

Assuming that this is due to lysozyme activity, the take-home here is a two part one:

First, lysozyme is very effective at preventing MLF. I had heard mixed opinions on its effectiveness, but it appears that it is quite potent.

Secondly, while a number of species of malolactic bacteria (including oenococcus) are sensitive to lysozyme, there are strains of malolactic bacteria which are tolerant of lysozyme.

It is good to know about these strains, though, for the future. There is always the possibility that I may need to treat a less-than-pristine lot of fruit with lysozyme but still want to put the wine through malolactic.

At this stage in the vineyard/winery cycle, I may not have the time to order and use them.

My plan, then, is to give this new inoculation of oenococcus a couple weeks. The other batch may have been expired.

If this fails to move the conversion, I will try a little bentonite to precipitate the lysozyme and pitch ML bacteria once more.

If there is still no progress, I will add SO2, do a light egg white fining to take the edge off the hard tannins and bottle.

Lessons learned.