A couple of weeks at the London Wine Fair a friend in the trade asked me how my home-made wine had turned out. I was flattered that anyone had not only read my previous blogs on this subject but remembered doing so six months later.
It is true that I have been neglecting both my half-made wine and updating this blog since then, in favour of other wine projects to be reported here in due course.
Parts 1 and 2 of this blog were about my little vineyard in London and making a 2018 vintage, my first. But the fermentation had stuck and part 3 was about unsuccessful attempts to restart it. The wine then sat in my wine fridge through the winter while I sourced some further materials and did more research.
It seemed likely that the yeast had consumed the glucose but baulked at the fructose, these normally being present in roughly equal quantities. Sure enough, when extra glucose (a.k.a. dextrose, available as a powder) was added, it was soon consumed by the yeast.
One recommendation is to treat the wine with lysozyme and then add fresh yeast. Lysozyme is an enzyme that knocks out certain bacteria. Our bodies produce and use it; there will be some on your tissue after blowing your nose or wiping your eyes. I don’t think lysozyme helps restart fermentation, but it helps prevent spoilage in a wine that had by now been sitting around longer than planned, and in warm conditions. Importantly, it doesn’t interfere with yeast, create any sensory impact or leave a toxic residue. Side effects: lysozyme can inhibit malolactic conversion, the usual secondary ‘fermentation’ for red wines, as well as some white wines. I wasn’t bothered, since I was making a rosé, which doesn’t go through malo.
The commercial preparation is lysozome hydrochloride, extracted from egg whites. It’s readily available, in Singapore from Guardian pharmacies as a self-medication, under the brand Leftose. “Dissolves phlegm in chesty coughs and reduces inflammation in sore throats.” As does waiting a week for both to go away. Anyway, one tablet contains 30mg and I needed about 300mg/L, so 18 tablets. These were crushed and dissolved in a little water and then added to the wine, which then went into the wine fridge for a week while I waited for its chesty cough and sore throat to be resolved.
Then fresh yeast was added (actually a number of different strains to separate batches of the wine), but all refused to ferment out the remaining sugars. It was time for further research as to the actual causes of stuck fermentation.
The front-runner is said to be an excess of short and medium chain fatty acids (SMCFA).
These can be reduced by adding dead yeast cells (yeast hulls or ghosts) to which they combine and precipitate. However, these are not available in Singapore, and this was the cause of the long delay before being able to report further activity here.
I have now brought a packet of yeast hulls back from London. It’s sold by Brewcraft USA as Yeast Energiser, which also includes nitrogen; a lack of that can also contribute to a stuck fermentation.
Before proceeding the wine was retested. First Brix (sugar content) was re‑measured and was found to have dropped from 5.5 to 4.5, good news. There had been some slow fermentation through the winter, and alcohol was up from 8.9% to 9.5% abv.
Re-measuring pH showed a negligible change from 3.0 to 2.9, just measurement error.
I also tested total acidity for the first time, using titration. In line with the pH, that came in at a high 10g/L TATA (total acidity expressed as tartaric acid). Red wine is typically in the range 6-7, with Pinot Noir at the higher end; dry white wine can be 7.5 and sweet white wine 8.5. So that’ll need fixing later, but first to deal with the supposed fatty acids.
The yeast energiser must be added at “1/2 tsp per gallon”; that’ll be a US teaspoon and a US gallon of course. I am convinced that the Americans resist moving to metrication because they think it’s a French invention which, by and large, it is: have you read The Measure of All Things? Anyway, the amount of energiser I need works out at 0.62 grams. I had bought a mini-kitchen scale for this project, with 0.01g display resolution, though I suspect not accuracy. (I use it mostly for measuring out a few grams of yeast when making bread.) So into the wine went 0.62g, shake it all around, and back in the wine fridge with it.
After 48 hours the wine came out of the fridge and was racked and filtered once more.
I also had to deal with the high acidity. At this point rules have to be broken. One is EU wine law, which forbids Chaptalisation (enrichment with sugar) and deacidification both being used – not that I am selling this wine, but it is a good quality guideline. The other rule is that this much deacidification is best carried out before fermentation, one reason being that yeast doesn’t like excessive acidity. Eureka! Maybe that’s contributing to my stuck fermentation?
Calcium carbonate, CaCO3, is used for deacidification. It’s a benign application of the reaction that’s causing sea coral to bleach and die from acidification of the oceans – while releasing CO2 as a double jeopardy. It’s just powdered chalk but yet again (together with glucose, casein and lysozyme) it is stocked by shops peddling dietary supplements, usually with various additives. How did mankind survive its first million years without these? I obtained mine, much cheaper and pure, from a garden shop, intended for reducing soil acidity; Singapore’s soils are generally acidic.
In order to enable a before-and-after taste test I treated only half the wine first. My target was 2g/L reduction in TA so I needed 1.1g of CaCO3.
The treatment protocol is not obvious. CaCO3 takes out primarily the tartaric acid, not the malic acid, leaving the wine susceptible to bacteria. So the dose is added to about a third of the wine (at triple strength) while the rest of the wine is reserved; then the two are combined. This leaves enough tartaric acid intact.
The reaction only takes an hour or so, then the treated wine is racked and filtered again and added back to the reserve. A comparative taste test showed a considerable improvement. The fruit had softened over the winter, and was now masked by a lemon juice character. This was absent in the deacidified wine and the red berries were back to the fore. The readings were as follows:
|Batch||% of volume||pH||TATA g/L|
|Untreated and Reserved||50% 33%||2.9||10.0|
So the target reduction to 8g/L TATA was exactly achieved; it would be strange were it not, or pretty close. Then the other half of the wine was treated in the same way, and the final TATA was 7.8, just right.
Well, this blog was going to be about restarting the fermentation, and that is the next step. But I’m going to take the wine back to London to do it, as the ambient temperature there is about right, whereas in Singapore it’s far too hot and the wine fridge too cool. So it may be a while until there is anything to say, and this part is already long enough; I’ve been keeping you away from your wine (or maybe not).