Winemaking 101 – Episode 6 C – 2019 second run, continued

Renewed Fermentation

When I racked the barrel on 03/28/2020, I discovered the specific gravity had dropped from 1.000 to 0.992. This is good, as the lower SG indicates that all sugar is consumed and fermentation is done. In addition, I like bone-dry reds, so this is a better taste (to me).

This also explained why the bung blew out a few months back — the yeast activated and consumed the remaining sugar, producing CO2. The increased pressure blew the bung.

Exploding Bottles!

Barrel still full!

Barrel still full!

Wine must be stable when bottled, else there is a danger of bottles exploding.

If the bottle is corked, the bottle won’t explode like a grenade. Instead the cork will be pushed out of the bottle and the wine will leak out or burst out, depending on how much pressure was built up before the cork popped. This wastes wine and makes a mess.

Screw cap bottles are more dangerous, as the bottle is likely to fail before the cap gives way. It is possible for the glass to burst.

I’ve never experienced it myself, but have heard second and third-hand stories of bottles literally exploding.

To prevent this, the wine must be stable before bottling.


Knowing the specific gravity is critical, hence why all reputable sources for wine making knowledge mandate use of a hydrometer. Your taste buds can be mislead, but the hydrometer won’t.

Dry Wine. If the SG is at or below 0.996, the sugar is consumed. There is nothing for the yeast to eat, so there will not be another fermentation. It’s safe to bottle.

If there is residual sugar or if a non-dry wine is desired? Preventing a renewed fermentation can be handled in multiple ways:

Sterile filter the wine. Commercial wineries filter the wine with a filter fine enough to remove all yeast cells. If there is no yeast, there is no new fermentation. This is tougher for home wine makers to do.

Jack up the ABV #1. Each variety of yeast has a limit to how much alcohol it can survive. If there is enough sugar available, yeast will continue to eat and produce alcohol until it poisons it’s own environment. One method is to continue feeding sugar to the wine, in small doses, until the yeast can’t survive in that level of alcohol. [The measurement used is Alcohol By Volume (ABV).]

Jack up the ABV #2. Distilled spirits, e.g., vodka, brandy, etc, can be added to the wine to increase the alcohol above the yeast’s limits. This is what is done with Port.

Sorbate. Potassium sorbate in combination with potassium metabisulfite can be added to a that is not actively fermenting to prevent a renewed fermentation. The common way for a home wine maker to make a non-dry wine is to ferment the wine to dryness. Then add sorbate/K-meta, and then sweeten to taste with sugar, honey, fruit juice, or other sweetening product.

What’s Next?

This part of wine making is boring. I will check the barrel every 3 to 4 weeks, topping it as needed.

Every 3 months I rack the wine out of the barrel, clean the barrel, then rack the wine back into it. At this time I add 3/4 tsp K-Meta as a preservative and anti-oxidant.

I will bottle the barrel this fall when I have a new wine to put into it.