Stalled fermentation

The wine after racking

The red wine (Rondo) had stopped bubbling so we assumed it had stopped fermentation. The sediment had settled nicely so we decided to rack it and naturally measured the Specific Gravity and Brix. Lo and behold, the SG was1.02 and the Brix reading was 14. Way too sweet for a dry wine, which was our objective. We tasted it and, although a lovely colour, aroma, and taste, definitely too sweet. 

So it was back to the book to determine what can stall fermentation. It turns out lots of things can stall fermentation. (p51 of First Steps in Winemaking lists at least 8 possible causes.) I didn't want to add sugar water as it was too sweet and I don't like the idea of diluting wine. One of the suggestions was to add more yeast. So I dissolved one level tsp of yeast nutrient in 1 cup of warm previously boiled water and added in one level tsp of brewer's yeast. I added one cup to each of the three gallon jugs of wine after racking. That topped off the container perfectly after racking and now one of the demijohns has already started bubbling. I am hopeful to complete the fermentation. 

1.02 SG

The white wine, which got the sugar water addition, is not doing much of anything. We might have to rack that again and do the same. 

Alex decanting wine left behind

The sediment

Correcting the sugar content

Looks like we messed up. 

Our red must has tested at just over 1.008 on the hydrometer and 5 on the Brix scale. That won't get us to the right alcohol content - too low. We should have added sugar to the must at the first stage but we didn't.

When making wine, the Start Gravity should be 1.070 (normal finished ABV will be 10.5%) to 1.090 (normal finished ABV will be 13%). Finish Gravity should be 0.990 (for dry wines) to 1.005 (for sweet wines).

Alex made a simple sugar syrup dissolving sugar in boiled water. We have to wait for it to cool to room temperature. 

Now we have to figure out how much syrup to add. Because I had to dilute the sugar solution by half to get the hydrometer to read the SG, the specific gravity of the syrup is 1.110 x 2  or 1.220. 

So to increase the SG to where the potential alcohol would be sufficient, we'd have to add 40 oz sugar per gallon or 2.5 lbs per gallon. That would be 1 l of water or 1.5 l of syrup. (Alex did the maths.)

Just as a note to self:  3 kg water plus 3 kg sugar = 1 demijohn.

So we expanded our two demijohns to three with the sugar syrup and must (stirred to keep the yeast equal) divided equally among the three. I tested the SG of the resulting must and it read SG 1.070. That should get us to over 9% ABV. 

Curiously, I just measured the SG of the Solaris must, and it, too, reads 1.008. Not surprising as it started out at the exact same SG as the Rondo must. So we'll have to repeat the procedure for the white. 

So we have 1.5 l of Solaris must, measured by weight. So if we need 40 oz sugar per 3.78 l above, we need:

40/3.78 = x/1.5 = 15.9 or 16 oz of sugar. We added 16 oz of sugar dissolved in 16 oz of water to the 1.5 l of must and essentially doubled the volume. The SG read 1.082, a little higher than the red but perfectly fine. 

Let's hope we have restarted the fermentation. At least we now have 1/3 more wine to bottle. 

Here are 10 more things that can go wrong in fermentation. 

https://www.brewersfriend.com/abv-calculator/ 

Adding sugar to control alcohol

Measuring SG with a hydrometer

When must ferments, it is turning sugar into alcohol. Last year, our wine was high in alcohol. This year, I think it will be lower and may need a boost. Less sugar in the fermentation equals less alcohol in the wine. 

Trying to control the alcohol content of your wine is not always necessary. Most recipes are designed to make a wine that is in balance and has an alcohol level that is appropriate to the wine’s traditional style.

Wine recipes often call for specific quantities of sugar. But if you are starting with grapes, adding half the sugar that a wine recipe calls for does not give you half the alcohol in the wine. This is because some of the sugar is coming from the fruit itself.

An easy way to get around this is to use this general rule of thumb when attempting to control the alcohol content of a wine:1 pound of sugar dissolved in 5 gallons of must will raise the potential alcohol content by approximately 1%.

“One pound of sugar added to 5 gallons of must will increase the wine’s potential alcohol by 1%.”

The opposite holds true as well.

Controling the alcohol content of your wine

The biggest problem with this generality is that it does not tell you what your potential alcohol level is  before you make any adjustments. If you are following a wine recipe that calls for a specific amount of sugar, it will only get you in a potential alcohol range, not an exact target. This is because the amount of sugar contributed by the fruit can vary.

The best way to adjust the beginning sugar level in your wine’s must is to use a wine hydrometer. Most gravity hydrometers have a Potential Alcohol scale that will tell you how much alcohol the sugar in your wine can potentially make. Knowing this will allow you to control your finished wine’s alcohol level with more precision.

What's the best alcohol level in the finished wine?

The wrong alcohol content can have consequences. Too little and your wine can spoil, too much and it can taste harsh.

The alcohol level of a wine should be at least 8%. Wine needs alcohol to keep contaminants in check. Over time, wines that have 5%-7% alcohol are more susceptible to spoilage and tend to turn brown.

You also do not want your wine’s potential alcohol to be more than 14%. There's a limit as to how much alcohol a wine yeast can tolerate. Shooting for an alcohol level that is beyond your yeast’s ability to ferment can result in either a stuck fermentation or a wine that is too sweet.

The Alcohol by Volume (ABV) is calculated by subtracting the start gravity from the finish gravity and dividing this figure by 7.362. For example, the starting point for our wine last year was 1.100 and if this fermented down to 0.990, the drop will have been 110 points. This divided by 7.362 is 14.94% ABV. In fact, we ended up with a very high alcohol content but not as high as the calculation. 

Raising the specific gravity (SG)

Raising the specific gravity of wine with sugar syrup is a good way to get the SG up to where you need it when making a wine that just needs a little boost. Knowing how much sugar syrup to add to the wine to get from point A to point B on a hydrometer scale is very useful. To do this you need to know the specific gravity of the sugar syrup. 

You can use a wine hydrometer to determine the specific gravity of the sugar syrup you make. Just put the hydrometer in a sample of the syrup just like you would when testing your wine. If the reading goes off the scale, add an equal amount of water and sugar syrup to a sample large enough to fill the cylinder in which you are doing your readings. Then take a gravity reading and times it by two.

As an example, after you added equal parts of water and sugar syrup, let's say you get a reading of 1.110. That would mean that the sugar syrup’s 'actual' SG is 1.220. You double the 'gravity' part of your reading because you cut the sugar syrup by half. 

Once you know the SG of the sugar syrup, raising the specific gravity of your wine with sugar syrup is just a matter of some calculations. 

Let’s say you want to add 6 ounces of sugar syrup that has a specific gravity of 1.300 to a gallon of wine:

A gallon of wine has 128 fluid ounces. You want to add 6 fluid ounces of sugar syrup for a new total of 134 ounces. Now you need to spread the gravity of (220 times 6) over the 134 ounces. So it is (220 X 6) divided by 134. That equals 9.8507. 

Let's make an equation

(Gravity of Syrup x Ounces of Syrup Per Gallon)/(128 + Ounces of Syrup Added) = Rise in SG

or

(220 x 6)/(128 + 6) = 9.85

There is a very good explanation and useful chart on this page. 

So if you are raising the specific gravity of a must with a sugar syrup that has a specific gravity reading of 1.220, and you add 6 fluid ounces of that syrup to each gallon of homemade wine, then the specific gravity of that homemade wine would be raised by 9.85 points on the gravity scale. For example, if the wine has a specific gravity of 1.060, the new reading would be 1.06985. You could round it to 1.070.  That yields a potential alcohol figure of 9.2. That's perfect!

I have ordered a book that many call the bible of home winemaking:  First steps in winemaking. It apparently covers this topic very well. 

Hydrometer Chart

Specific Gravity (SG)	Potential Alcohol (PA) % by Volume	Amount of Sugar Per Gallon
1.010	0.9	0 lbs. 2 oz.
1.015	1.6	0 lbs. 4 oz.
1.020	2.3	0 lbs. 7 oz.
1.025	3.0	0 lbs. 9 oz.
1.030	3.7	0 lbs. 12 oz.
1.035	4.4	0 lbs. 15 oz.
1.040	5.1	1 lb. 1 oz.
1.045	5.8	1 lb. 3 oz.
1.050	6.5	1 lb. 5 oz.
1.055	7.2	1 lb. 7 oz.
1.060	7.8	1 lb. 9 oz.
1.065	8.6	1 lb. 11 oz.
1.070	9.2	1 lb. 13 oz.
1.075	9.9	1 lb. 15 oz.
1.080	10.6	2 lbs. 1 oz.
1.085	11.3	2 lbs. 4 oz.
1.090	12.0	2 lbs. 6 oz.
1.095	12.7	2 lbs. 8 oz.
1.100	13.4	2 lbs. 10 oz.
1.105	14.1	2 lbs. 12 oz.
1.110	14.9	2 lbs. 14 oz.
1.115	15.6	3 lbs. 0 oz.
1.120	16.3	3 lbs. 2 oz.
1.125	17.0	3 lbs. 4 oz.
1.130	17.7	3 lbs. 6 oz.