The Basics of Fermenting Wine

The Basics of Fermenting Wine

Fermentation is anaerobically (without oxygen) breaking down sugars into alcohol or lactic acid. Carbon dioxide gas is often produced as a byproduct. Fermentation by bacteria or yeast is used to make a variety of foods such as yogurt, cheese, sauerkraut, sourdough bread, some hot sauces, kimchi, kombucha, wine, and beer.

There are two ways to perform alcoholic fermentation: naturally occurring wild yeast or commercially available yeast that you add to a ferment. I prefer using commercially available yeast as your ferment has less risk of spoilage or off flavors. However, many people enjoy trying wild ferments.

When to Pick Your Grapes

There are several factors that determine when to pick your grapes: Brix, pH, and TA. Brix is the percent sugar. I try for 24% for my red wine grapes to get a ~14% ABV. The higher the starting sugar, the higher the potential alcohol concentration at the end of fermentation, assuming you ferment to dryness. You generally want at least 18-19 Brix for white wines to end up with 10-11% ABV.

​pH is the strength of the acid in the grape juice. A pH of 7 is neutral, less than 7 is acidic and higher than 7 is alkaline or basic. White wines are generally more acidic than red wines, with a pH usually between 3.0-3.4. Red wines ideally are between pH 3.3-3.6. If you are using fruits other than wine grapes you may need to significantly alter the Brix and/or pH to achieve an acceptable wine.

Total acidity or TA is the amount of acid in a solution, but, as stated above, pH is how strong that acid is. You could have a lot of acid that is not very strong, or you could have relatively small amounts of a stronger acid. TA is measured in grams per liter (g/L), not the pH scale. Wines grown in northern climates tend to have a lower Brix, higher pH (more acidic), and higher TA (more acid in total). As the grapes mature, their sugar concentration increases, and their acid levels decrease.

Last year (2023) we picked our grapes early because they were being destroyed by birds and then wasps. We bought bird netting before we realized the wasps were also a problem. Because we picked early, our Brix was low (~18), as was our pH (~3.0), for red wine. We added sugar to achieve a Brix closer to 24. Our TA was also what would be considered high for grapes grown in California (~9 g/L), but this was actually surprisingly low for Marquette grapes. This year (2024) we bought insect netting that kept the majority of birds and wasps off our ripening grapes and so we picked later in the season. Final numbers after crushing the grapes were 22 Brix (the grapes tested at 24 but we only sampled a few grapes, not entire clusters), 3.4 for pH, and 11+ g/L for TA. The TA is too high, but in line with what you generally see for Marquette grapes, but the pH and Brix were better. I again added a little sugar to achieve roughly 24 Brix. I am hoping that by using a yeast that reduces acidity (see discussion below) and following alcoholic fermentation with malolactic fermentation, I can reduce the TA to a more acceptable level.

Yeast Selection

What yeast you choose depends on many factors including what type of wine, beer, or cider you want to ferment, what alcohol content you are hoping to achieve, what temperatures you will be fermenting at, etc. There are specific yeasts for beer versus wine and even red, white, or fruit wines.

EC-1118 is a commonly used yeast because it has high alcohol tolerance (up to 18%), it rarely gets stuck (stops fermenting), gives a neutral flavor, ferments at a large temperature range (45-95°F), and is good for a variety of wine styles even though it is traditionally considered a champagne yeast. It is commonly used for reds, whites, and cider as well.  EC-1118 is not a good choice if you want to follow alcoholic fermentation with malolactic fermentation as they are not compatible and high alcohol levels can also inhibit malolactic fermentation.

I use Lalvin 71B for my Marquette wine (even though it is traditionally used for white wines) because it is compatible with malolactic fermentation, which is commonly used for red wines, especially acidic grapes like Marquette. Both 71B and malolactic fermentation reduce the overall acidity (TA) of wine. 71B can neutralize up to 40% of malic acid found in juice and malolactic fermentation can neutralize much of the rest, creating a smoother wine. One potential disadvantage of 71B is that its alcohol tolerance is 14%. If you want higher alcohol wine, this is not a good choice.
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Other options for red wine include Bourgovin RC-212, Premier Rouge, and ICV D254. I have used RC-212 for my elderberry wine with good results. Fruit wines (other than grape) are often fermented with K1-V1116 but it can also be used for white wine. Other traditional white wine yeast includes Premier Blanc, Cote des Blancs, and ICV-D47.

Grifo brand grape crusher/de-stemmer (left), wine press we bought used (center), air lock bubbling on the lid of a fermentation bucket (right).

Equipment and Supplies

You can either buy your equipment and supplies individually or many homebrew shops sell kits with much of the equipment and grape juice, or beer ingredients included. What kind of equipment you need depends on what you want to brew, wine or beer, but they do share much in common. I have only brewed beer from kits (I have never done all-grain brewing) but I have made wines from both kits and whole fruit. Most techniques are similar; however, beer uses grain or grain/malt extracts while wine uses whole fruit or juice. Here I will cover the basics of general wine fermentation as that is what I have the most experience with, but I also plan to post about making wine from our Marquette grapes in particular in the future.

1. Fruit or juice – If you choose to buy fruit juice make sure there are no preservatives added (potassium sorbate, sodium benzoate, sodium/potassium metabisulfite, sulfur dioxide, and probably more) as this will inhibit your fermentation. Sodium/potassium metabisulfite is commonly used in wine fermentation to prevent wild yeast and other microorganisms from growing but you do not want too much or it can still inhibit even commercially purchased wine yeast which was bred to be resistant to it.
2. Cleaner/Sanitizer – Potassium metabisulfite is commonly used for wine, sodium metabisulfite is also an option but many avoid it due to the sodium content.
3. Hydrometer with a test jar or graduated cylinder - A hydrometer is used to measure the specific gravity before and after fermentation. The specific gravity readings can then be used to determine alcohol concentrations and if the fermentation has been completed. You float the hydrometer in a sample of your juice (pre-fermentation) or wine (post-fermentation) and take a reading. More information on how to interpret those readings is given below.
4. Refractometer (optional) – We bought a digital refractometer (cheaper manual ones are also available) to measure the Brix (percent sugar) in our grapes so we know when to harvest them. This can be used on other fruit juices as well, but it does not give accurate readings once fermentation has begun since alcohol affects accuracy. The advantage of a refractometer is that you can test much smaller juice samples so you do not need to sacrifice large numbers of grapes to determine their sugar content as you would need to with a hydrometer.
5. Thermometer - A thermometer is helpful so you know if your ferment is too hot (vigorous ferments can get really hot!) or too cold. The optimal temperature depends on the strain of yeast you choose.
6. Fermenter – Fermenters are often plastic buckets with a tight-fitting lid and an airlock. These can range from 2-gallon buckets for 1-gallon ferments, to 5-8 gallon buckets for 3-6 gallon ferments. The bigger your volume the larger headspace you need. You can also buy bigger buckets or stainless-steel fermenters, but most homebrewers stick with 8 gallon buckets as their maximum size as these are easier to move around, lift, transfer, etc.
7. Airlocks – Because fermentation is an anerobic process you want to use an airlock, usually a plastic piece that holds water or other liquid (many people use potassium metabisulfite or vodka to keep it sterile) in it to block the air from entering your fermenter. If you have air in your fermenter, you increase your chance of mold formation (which is an aerobic or oxygen-loving microbe).
8. Mesh bags – Mesh brew bags are useful when fermenting with whole fruit to help contain the fruit debris when pressing. Some people also use them when fermenting as you can just pull out the bag, and let it drain some, before pressing, without having to dump your bucket of wine, grape skins, and lees (residue of spent/dead yeast and other particles that fall to the bottom during fermentation and aging) to get it out.
9. Carboy – Either plastic or glass carboys are used for secondary fermentation or aging of wine. Carboys have a narrow neck to eliminate as much airspace as possible.
10. Bottles – Wine bottles are traditionally 750 ml but you can also buy bigger 1.5 L or smaller 375 ml bottles. You can buy them in different colors, clear, green or brown are the most common but blue and red are also available. Some wine, like Pinot Noir or Chardonnay, is traditionally bottled in Burgundy bottles with sloped shoulders. Whereas many other wines, including reds such as Cabernet Sauvignon, Merlot, and Malbec, are bottled in Bordeaux bottles, which have more pronounced shoulders. Sauvignon Blanc, a white wine, is also bottled in Bordeaux bottles. Hock or Alsace wine bottles are elongated versions of Burgundy bottles and are traditionally used for Riesling, Gewurztraminer, and dessert wines.
11. Bottle corker – We have a floor corker for our wine, while more expensive than a hand corker, is much easier to cork wine bottles with, even my child (starting about age 10) can operate ours.
12. Autosiphon with Tubing – An autosiphon is used to create a suction to transfer the wine from one vessel to another also called racking. Racking removes the wine from the lees, including spent yeast on the bottom. We stopped using the autosiphon when we found tubing with a ball type valve on the end. By quickly jiggling or shaking the ball valve in the wine it starts the siphon. We found this system easier to use except with small one-gallon batches or if there was lots of debris on the bottom which could clog the opening.
13. Spring-Tip Bottle Filler with Tubing – A bottle filler is used to fill the bottles when you are ready to bottle your wine. The spring tip allows you to open the filler when it is pressed down on the bottom of the bottle but then quickly stops the flow when you lift up on the filler.
14. Corks – We usually use #9 corks for our 750 mL bottles and drop down to a #8 cork for 375 mL bottles which have a slightly smaller opening. Most corks are designed to store wine for up to 2 years. If you want longer-term storage you will want to invest in better premium corks which will last longer. If you use cheaper corks, and then decide you want to store longer, you can always recork by removing the old cork, squirt in a little potassium metabisulfite to preserve the wine from exposure to oxygen, and then re-cork with a premium cork.

Marquette grapes in the hopper of the crusher/de-stemmer (left), grape juice, skins, and seeds after crushing (center), wine ready to be pressed in a mesh bag (left).

Where to Buy Fermentation Equipment, Supplies, and Kits

Where to buy fermentation supplies depends on where you are located. I often buy from a local shop, however, it is not a designated brew shop, so their supplies for some products are limited. For more specialized supplies I need to buy online.

1. Local Shops – Our local shop has the basics but is not a designated brew shop, so I have to buy more specialized supplies online.
2. Northern Brewer – I like Northern Brewer because they are based out of Minnesota, which is only a couple hours from where I live so shipping is quick. https://www.northernbrewer.com/
3. Midwest Supplies – I also like Midwest Supplies because they are based out of the Midwest so reasonably local for me. They have recently partnered with Northern Brewer so they are the same company but you can still order from both websites. https://www.midwestsupplies.com/
4. Phoenix Brewing Supply – Although not local I recently purchased from Phoenix Brewing Supply via Amazon because they had malolactic bacteria and nutrients that I could not find other places. After purchasing off Amazon, I placed a second order for more specialty nutrients and tannins directly from their website. They get their orders shipped out quickly, although it takes shipments a couple of days longer to get here due to their distance from me. https://phoenixbrewingsupply.com/
5. Amazon – If I need something quickly, I’ll order from Amazon. 

Our first glass of Marquette wine fermented from our grapes in central Wisconsin.

How to Ferment

If you bought a wine kit your best option is to follow the instructions that came with the kit. Here I will cover the basics of making fruit wine from scratch, either using grapes or other fruits.

1. Juice – Buy juice, fruit to make the juice, or pick the fruit if you grow it. If you buy juice it needs to be preservative-free, this can be hard to find. If you are using whole fruit, you need a way to extract the juice. There are multiple options to extract juice. If you are making grape wine the traditional way is to crush and de-stem your grapes. You can do this manually (I’ve used a potato masher) for small batches. This also works well for other easy-to-crush fruits like berries. We bought a grape crusher-de-stemmer which we use for large batches of grape wine now that our Marquette grapes are making about 60 pounds of grapes/season. Be sure to clean all your equipment with potassium metabisulfite to kill any wild bacteria and yeast. Another option which I use for elderberry wine is to use a steam juicer. The advantage of this method is that it is easy, the disadvantage is that it does cook the juice, which is not traditionally done for grape wine. This method could also be used for fruits that are harder to crush like apples, to make apple juice/wine.
2. If you are starting with straight juice, without skins, you can skip right to fermenting. If you have skins mixed in, like grape skins, you either press immediately for white wine, allow the skins to sit with the juice for a short period for a rosé wine, or ferment with the skins and press a week to 10 days later for red wine. I mostly ferment red wine so I will discuss fermenting first and then pressing.
3. After you have crushed your grapes or acquired juice you need to ferment. I buy 5-gram packs of yeast, which is enough for up to 5-6 gallons of wine. What yeast you choose depends on many factors (see above).
4. Before fermentation use potassium metabisulfite (either use the powder or Camden tablets in distilled water) mixed into your juice to kill any wild yeast. In generally you can use up to 1 Campden tablet/gallon of juice, however this may overly sulfite your wine. If you want more exact measurements, I recommend using a sulfite test kit along with a sulfite calculator which takes pH, volume, red vs white wine, etc. into consideration. You then wait 24 hours before pitching your yeast. If I extract my juice with a steam juicer, I skip this step because the steam has killed any wild yeast, I simply make sure my juice has cooled down enough (~70F) before pitching the yeast. I do add sulfites after fermenting though as the sulfites not only prevent microbial spoilage, but also prevent oxidation. If you are planning on malolactic fermentation during or following primary fermentation, limit the sulfites added as this can inhibit the malolactic bacteria.
5. You may also need to adjust sugar or acid levels before fermenting. A general rule is to add 1.5 oz of sugar to raise 1 gallon of must by 1 Brix. Add less sugar than you think, mix well, and then test your specific gravity/Brix again. Sometimes I add sugar to get just under my intended Brix, add the sulfites, and let it sit overnight before testing the Brix again as more sugar can be released overnight as the grapes break down more. If making a fruit-based wine other than grape, you may also add some water to the juice, however, pure juice will give the strongest flavored wine. Generally, you want at least 3 pounds of fruit per gallon of wine. You can measure the sugar level with either a hydrometer or a refractometer. If you are using a hydrometer, you put juice in your graduated cylinder, place the hydrometer in the juice and read the specific gravity (read at the bottom of the meniscus). Most juice for white wine should be between 1.070 and 1.090 which correlates with 10.5% to 13% alcohol by volume (ABV), respectively. For red wine you want between 1.085-1.100, which gives ABV between 12.5- 14.5%. When using a refractometer, the Brix or percent sugar reading multiplied by 0.55 gives an estimated ABV. Generally, you want Brix to be between 19-25 giving 11-15% ABV depending on your wine style.
6. When adding your yeast, first mix your yeast with a yeast rehydration nutrient that has been rehydrated in distilled water, such as GoFerm , let it start foaming (replicating) and then pitch it. However, I have also had good luck simply sprinkling the yeast on top of the juice, although this can shock the yeast more.
7. After pitching the yeast, gently stir it in, close the lid and insert the airlock. I fill the airlock with potassium metabisulfite solution so there is no risk of it becoming contaminated.
8. Usually, 24 hours after pitching the yeast I see fermentation begin as indicated by a bubbling airlock. However, it is not unusual to see no activity if your gasket around the airlock or the lid leaks. If you see a cap of skins rise up or lots of bubbles when you stir the juice/wine then it is likely fermentation has begun. You can also use your hydrometer to see if the specific gravity is decreasing (which indicates a reduction in sugar caused by fermentation). Remember, a refractometer does not give accurate results once fermentation has begun. If you did not leave enough headspace or your ferment is unusually vigorous your juice may bubble into the airlock. Be sure to clean out your airlock, add fresh potassium metabisulfite and re-insert the airlock. You may not want to close the lid tightly again until after fermentation has slowed. You can also move some of your must into a second fermenter to eliminate overflow.
9. I stir the ferment twice daily. This helps extract the color from the grape skins by mixing them into the solution as the skins tend to float to the top and form a cap. This is equivalent to “punching down” or pumping over. If you are fermenting juice only, no skins, I still stir occasionally but this is not as important as you are not worried about color extraction from the grape skins.
10. Usually, after a week to 10 days the ferment has slowed significantly. You can now take a specific gravity reading to see how far your ferment has progressed. A finished wine is usually in the 0.990-0.960 range. I do not usually bother to check the specific gravity unless I suspect the fermentation has become “stuck”. To use your original gravity (OG) and final gravity (FG) readings to determine your estimated ABV use the formula: (OG-FG) x 131.25. At this point I either rack my wine into a glass carboy if there were no skins or I press the wine to remove the skins and then siphon it into a carboy.
11. To press I pour the wine (with the skins) into a mesh bag. I then press the wine/skins in the mesh bag. The bag helps prevent loss of the skins back into your wine when pressing. If you do not have a wine press you can manually squeeze out the wine using your hands after letting it drip for a while.
12. After pressing, move the wine into a carboy. At this point fermentation has dramatically slowed so you want to reduce the headspace as much as possible to reduce oxygen contact with the wine. If you need to reduce headspace you can use clean marbles to take up space (I have had the marbles break a carboy when bouncing into it) or use a similar wine to top up your wine (the preferred method). If you are not planning on completing malolactic fermentation you should measure the sulfite levels and add more as needed.
13. At this point you can perform malolactic fermentation, which is more complicated, at least detecting whether it has worked, than regular yeast-based fermentation. Some people also do malolactic fermentation partway during primary fermentation. Malolactic fermentation can take weeks to even months to complete and is very sensitive to sulfites. If you are doing malolactic do not add any more potassium metabisulfite, otherwise adding another dose is recommended.
14. During secondary fermentation (which is basically just waiting for fermentation to complete) I add oak chips, cubes, staves or spirals if desired. Chips are the cheapest, but I find they get in the way when trying to rack later on and are annoying to clean out of the carboy. I have switched to cubes recently and others like the staves or spirals because they can tie fishing line to them to remove them from the neck of the carboy if they want to stop oaking without having to rack the wine. The spirals have a greater surface area so oaking will finish more quickly.
15. Oaking is generally done for weeks to months depending on how strong the oak is and how much oak characteristics you wish to impart on your wine. You can also purchase oak barrels, but they are very expensive and do require maintenance when wine is not aging in them.
16. At this point I rack only when noticeable debris starts accumulating in the bottom of the carboy. You can let the wine age in your carboy with occasional racking and potassium metabisulfite additions (do not forget to keep an eye on the airlock, or switch to a bung when the fermentation is for sure complete) for months to years. I am usually impatient and probably bottle too quickly once the wine has clarified (unless I forget about them). You want to age in a cool dark place, I use a basement closet that is probably mid-60s. Most red wines are aged at least a year before bottling. Aging can also occur in the bottle to some extent but further oaking is impossible. You should also check sulfite levels every 6 months while aging to see if additional sulfite is needed.
17. An optional but recommended step is to cold-stabilize your wine. This helps bring any small particulates and excess acid out of solution. It also reduces sedimentation in the bottle, especially if they are stored in a cooler location or transported in colder weather. We usually place our carboy in an extra fridge but if you live in the north, you can place your carboy outside in the winter. Last year (2023) after putting our Marquette wine in our fridge we saw LOTS of acid crystallize out, and our wine still ended up excessively sour/acidic (we picked our grapes earlier than desired due to bird/wasp damage, hopefully it will mellow with storage).
18. If you do not want to wait for wine to clarify on its own or it does not seem to be clarifying, you can add various fining agents, such as bentonite, to the wine to help it clarify. You can also filter it, but this requires more specialized equipment.
19. Before bottling it is recommended you test sulfite levels again and add more as needed. I clean all the bottles, tubing, and bottle filler with hot water and then potassium metabisulfite.  To bottle I use siphon tubing with the bottle filler to fill each bottle to the top. When you remove the filler from the bottle the correct amount of headspace is left in each bottle.
20. After bottling cork each bottle, or cork as you go if you have more people helping. Let the bottles stand upright for a few days before you store them on their sides (the corks have to re-expand after being squeezed during corking).
21. I usually start tasting my wine after a minimum of 3-6 months in the bottle. I usually bottle some of the wine in the smaller 375 ml bottles which I open occasionally to taste. If the wine is not ready yet I did not waste a larger bottle of wine. Red wine is usually best after 1-2 years aging but longer is not unusual. Some commercial red wines are aged 10-20 years. White wines generally do not need aging as long and should be consumed withing 2-3 years but full-bodied white wines are often aged longer, for 3-5 years.

References and Resources

1. Cox, Jeff. From Vines to Wines: The Complete Guide to Growing Grapes & Making Your Own Wine. 5th Edition. 1999/2015. Storey Publishing.
2. Pambianchi, Daniel. Modern Home Winemaking: A Guide to Making Consistently Great Wines. 2021. Vehicule Press.
3. Pambianchi, Daniel. Techniques in Home Winemaking: The Comprehensive Guide to Making Chateau-Style Wines. 2008/2022. Vehicule Press.
4. Sulfite Calculator. WineMaker Magaszine. https://winemakermag.com/resource/1301-sulfite-calculator
5. Wine Calculators. Techniques in Home Winemaking.  https://techniquesinhomewinemaking.com/winemaking-tools/