Gavin V. — GA
I’m assuming that you are referring to our resent blog post on ways to reduce head-space in a fermenter.
Certainly, topping up wine with concentrate is something that can be done, however realize that you are adding sugar. In fact, the concentrated grape juice is mostly sugar.
If the fermentation has completed, this will add more fuel for it to start up again. For this reason it is important that a wine stabilizer such a potassium sorbate also be added along with the concentrated grape juice. This will help to eliminate the chance of your wine having a re-fermentation.
If the fermentation has completed you do not want it starting up again. You will also need to take into consideration the more-obvious issue – that is – the concentrated grape juice will make the wine sweeter. If you want your wine to be dry, this would not be what you’d want to use top up your wine.
If the fermentation is still going, then adding the concentrated grape juice will increase the potential alcohol of the fermentation. There is always the possibility of raising the alcohol level too much, bringing the wine out of balance. Very seldom will you ever want the total potential alcohol of a wine to go over 13%, and only then if your wine has a lot of flavor. Wines with higher alcohol will have a tendency to taste hot and less flavorful.
It is also important to understand that topping up wine with concentrate will also add more acidity to the wine. Just like there is a lot of sugar in the concentrated grape juice, there is a lot of fruit acid. It is possible that using it to top up your wine could make it too tart or sharp tasting. This is the case regardless if the wine is still fermenting nor not.
So, if your wine must is low in acid and you like your wine’s off-dry or even sweet, then topping up your wine with a grape concentrate may be a good option. But, other than this scenario, I do not think this is a great option for you.
Regular grape juice would be a much better choice.
Since the regular, un-concentrated, grape juice will have about the same acidity level as a wine, blending the two will not change the tartness of the wine to any noticeable degree.
The sugar will still be a consideration. If you want your wine to stay dry as it would normally be after a fermentation, then grape juice – concentrated or not – would not be what you want to use. On the other hand, if you like your wines a off-dry or the wine is still fermenting, then grape juice might be something to consider.
Ed Kraus is a 3rd generation home brewer/winemaker and has been an owner of E. C. Kraus since 1999. He has been helping individuals make better wine and beer for over 25 years.