In the primary fermentation, yeast grow and consume most of the sugar in the juice. The yeast carry out a number of different biochemical reactions, most notably the formation of carbon dioxide and alcohol from the sugar. They will continue to do this until they run out of sugar or they are killed by the alcohol, whichever comes first.
Alcohol tolerance of wine yeast ranges from 14-18%, and most wine is 10-14% alcohol, so usually the primary fermentation is set up so that the yeast will run out of sugar first. If you want a sweet wine, you can wait until the fermentation is done and add sugar (i.e. “backsweeten”). In this case, a preservative (sorbate) is needed to prevent the fermentation from restarting. Sorbate does have a bit of a taste itself (usually described as “bubblegum”), and if you don’t want that in your sweet wine, you can start with a yeast that will die at 14% alcohol and leave some sugar behind. Or you can make a wine that is both sweet and very high in alcohol.
Although the yeast need oxygen to get going, once they’ve made wine, it is susceptible to damage by oxygen. Wine in oxygen becomes vinegar. Once the primary fermentation is in full gear, the carbon dioxide that is produced forms a protective blanket of gas over the wine. Once the primary fermentation slows down, you need to transfer the wine to a sealed container (a glass or plastic carboy) to finish fermenting. The fermentation in the second container is sometimes called the secondary fermentation, although it’s really a continuation of the first.
Because the primary fermentation requires oxygen at first, it is done in an unsealed container. For small batches, I use a 2.5 gallon food storage canister, and for larger batches, I use a 5 gallon food-grade bucket. You can get these from Lowes. Make sure it’s a food-grade bucket or your wine will taste like plastic. Mine has a sticker on the side identifying it as food safe.
For the juice, I’m using a mixture of Welch’s white grape and a large (96 oz) can of apricot fruit wine base. I usually use three cans of frozen Welch’s per gallon. For this batch, I’m using nine cans of Welch’s plus the apricot base in five gallons total.
The bucket should be thoroughly washed and sanitized, preferably with an oxygen bleach, as it rinses better, but regular bleach will work if you rinse well. Once the juices are in the bucket, I fill it with water, but not quite all the way. I went to about 4-1/4 gallons total. This is because the apricots don’t have nearly as much sugar as do grapes, and so I need room to add some so that the yeast will be able to make enough alcohol to preserve the wine — about 10%. I’m aiming for a low-alcohol wine — about 11%. I calculate that I need to add 1398 grams of sugar (plus enough water to fill to five gallons) to accomplish this. How do I know this? I’m glad you asked, because it allows for some science content.
This is a hydrometer floating in a tube of the juice.
It measures the specific gravity of a solution. Specific gravity is just the density of the solution relative to water. The specific gravit (SG) of water is 1, and so a solution that has a SG of .95 has a density 95% of that of water. Because juice is water with stuff (mostly sugar) dissolved in it, it is more dense than water. If you put a can of (non-diet) coke in a tub of water, it will sink because the sugar makes it more dense than the water. So the SG gives us a pretty good idea of how much sugar is in the juice and therefore how much alcohol the yeast can produce. The more sugar, the more dense the solution, the higher the hydrometer floats. There are marks along the length of the hydrometer giving the density at that level Neat, isn’t it?
Here is the hydrometer floating in my 4.25 gallons of juice:
You need to blow away those bubbles to get a good reading, but even with them, you can see that the specific gravity is 1.055.
Now we need to calculate the amount of sugar we need. There is a nifty calculator for this here. Just click on the “alcohol” tab, then the “hydrometer SG drop” tab. Adjust the temperature settings. Your hydrometer will be calibrated for a particular temperature, and it will be written on the side. A thermometer in the juice will give your actual temp. If you plug in an initial SG of 1.055 and a final SG of 0.099 (which is as low as it seems to typically go, although theoretically it can go lower), you get a little less than 9% alcohol — not enough to preserve the wine. If you play with the “starting SG” number, you’ll find that 1.075 will give about 11.5% alcohol. This is what I’m going for. Even if the wine only ferments to 1, I’ll still be a bit over 10% and therefore the wine will still be preserved.
Now click the “sugar” tab and choose “specify target SG and volume.” My target SG is 1.075, my target volume is 5 gallons and my SG now is 1.055. My initial volume is 4.25 gallons. Plug all that in and I need 1398 grams of sugar
Here’s my scale with the sugar:
Because I’m just guessing at the 4.25 gallons, I mixed the sugar with water and boiled it to make a syrup, then poured it into the juice and stirred it up. If you don’t make a syrup, the sugar sits at the bottom and you can’t get an accurate SG reading.
Here is the hydrometer in the sugared juice. The reading is a bit low, but if you correct for the warmer temperature, it’s perfect:
Now is a good time to hydrate the yeast. I put a little of the juice in a small dish, warmed it in the microwave, and poured in the yeast.
The yeast packet says 105-109 degrees F, so this should be fine. I’m using Lalvin ICV D47 yeast, which is good for making fruity wines. The yeast needs time to hydrate, and does this much better at warm temperatures. Set the yeast aside and add it at the end.
I added five teaspoons of yeast nutrient, which is not absolutely necessary, but it’s not expensive, and it can keep the yeast from being stressed. Stressed yeast can make bad smelling chemicals.
I also tested for titratable acid and added 7.5 teaspoons acid blend to get to 0.6%. This is also not absolutely necessary, but fruity wine is better with some tang to it, and the acid is also a preservative. I used this kit to test for titratable acid. Some day I’ll explain the science of it, but this post is already getting too long.
I added 1/2 teaspoon grape tannin, which will add a bit of astringency. Again, this is not necessary. I used 1/4 teaspoon pectinase, which is necessary because I’m using fruit, and it breaks down the pectin that can cloud the wine. If you’re just using juice, you can skip this.
Finally, it’s time to pour in the yeast.
Now my five gallon bucket is very full. Too full. Fermenting wine gets foamy. I transferred one gallon to a smaller container, and will combine them in the next step.
I let the wine sit on a heating pad on low for 24 hours and then added 1 crushed campden tablet per gallon. These tablets contain sulfites, which will keep undesirable microorganisms from growing. The reason I waited is to allow the yeast time to grow. If you hit them with the preservative right off the bat, you might kill enough of them to prevent the fermentation from starting.
In case you’re wondering, the cost of ingredients is:
9 cans frozen Welch’s white grape ($2 each) = $18
Can of apricots = about $40 with shipping
Yeast, nutrient, tannin, etc = about $5
Total about $63
Five gallons will make 25 bottles
$63/25 = $2.52 per bottle.
Now I just need to wait for the yeast to grow and ferment. To be continued!