To winemakers, the task of determining when to harvest grapes is a scientific process involving the pH of the grapes when between 3.2 and 3.5, and the sugar content, known as brix, between 20 and 25. But how do individuals with a few grapevines in their yard tell when it is time to pick their grapes for eating, making jelly, or juice?
When To Harvest Grapes
Generally, harvest time for grapes grown in the Northern hemisphere is from August to November, while in the Southern hemisphere, it is from March to August.
Harvest falls between 30 and 70 days after fruit set, but the timing is determined by a combination of several factors:
- Length of the growing season– Grapes ripen faster in warmer areas and slower in cooler climates.
- Type or variety of grapes being grown– Not all varieties of grapes ripen at the same rate. Some ripen early, some late.
- Flavor needed for the use– If making raisins, they should be picked when fully ripe and when the sugar content is the highest. If making jam, picking a few days early while the taste is a little tart will make better jam. If making wine, the grapes should be picked to provide the wine’s flavor: more acidic for sparking, so picked early; picked a few days later for white wine, picked last for red.
- Crop load– Crop load means the amount of fruit per vine. The smaller the crop load, the better the quality of the fruit.
Specifically, individuals who are fortunate enough to have grapes growing on their property can determine when it is time to pick their grapes by a few simple methods, but keep in mind that taste is the most reliable test:
1. Berry Color
A visual inspection is one of the better ways of knowing when grapes are ready for harvest.
Before grapes begin to ripen, their color is green and then lightens to almost white. But once they are closer to ripening, they will begin the process of changing to their natural color, which depends on the variety as to whether they become red, purple, dark blue, yellow, orange, black, or green.
The color change occurs 1 to 3 weeks before the grapes are fully ripened.
That color change is prompted by the increasing levels of sugar content. As the sugar level rises, the deeper the color becomes.
Plus, during the color change, the stems and seeds will turn brown.
2. Berry Fullness
A visual inspection will also determine whether the berries have become plump.
Before they are ready for picking, the berries are small and hard, and berries that are shriveled are overripe. But, berries that are plump and juicy and give a little when squeezed are just right for picking.
So a visual inspection can narrow down the time for the grape harvest in several different ways.
3. Taste Test
Once the berries appear to be soft, plump, and juicy and have reached their natural color, a simple taste test to check how sweet they are is another indicator that harvest time is just around the corner.
A good rule of thumb is to start tasting 3 to 4 weeks before the projected harvest date and taste often until they are ready.
Taste grapes from different areas of your vineyard, such as part shade and full sun, because those conditions will affect the ripening process, causing them to ripen at different rates.
4. Easy Release From The Vine
In addition to checking for color change, the plumpness of the berries, and whether they are becoming sweet, picking a few berries will give you another hint that harvest time is near.
When grapes are ripe, they release easily from the vine and are easy to pull from the cluster.
5. Using Sugar Content & pH Testing Tools
Wine makers are not the only ones who can use tools to determine whether their grapes are ready for harvest. Sugar content is measured by a tool called a refractometer and pH level is measured by a pH meter. The pH meter mentioned here is the same one used by Minneopa Orchards.
The refractometer and the tool for testing pH level are both inexpensive and easy to use, making the scientific method of targeting harvest time available to everyone.
How To Harvest Grapes
Grapes are either harvested by hand or by machine. Here are the basics of both methods:
Hand-picking grapes is slower and less efficient. But, hand-picked grapes are of higher quality because the best grapes are being selected for harvest by the pickers.
To hand-pick grapes:
- Start at the top of the cluster where the stem meets the large vine.
- Cut the clusters off with a garden pruner or scissors, don’t pull or tear them off by hand.
- Choose only the best grapes, avoiding those that are sun damaged or have vine rot.
- When picking, place the picked clusters in a bucket or basket to protect them after they are picked.
Tools needed for hand picking:
- Garden pruner or scissors
- Bucket or basket.
Machine picking, which was introduced in the 1960s, is more efficient than hand picking—the machine harvests grapes by moving down the rows shaking the grapes off the vine. But, if the grape orchard is on uneven ground, it is difficult to use picking machines.
To machine pick grapes:
- As the machine moves along, straddling the rows of grape vines, flexible fiberglass rods shake the vines.
- The grapes that are shaken from the vines run down a conveyor belt into bins along the sides of the machine.
- The bins are emptied at the end of each row into a larger container that is attached to a tractor that takes them to be processed.
Leave Grapes On The Stem Or Remove Them?
Grapes that are machine picked are removed from the stems when they are picked and should be processed right away.
Hand-picked grapes, however, should be left on the stems until you are ready to use them. They last longer that way.
Do Grapes Ripen Faster On The Vine Or Off?
Unlike other fruits like bananas, peaches, and avocados, grapes will not continue to ripen after they have been removed from the vine. So, before they are harvested, they should be fully ripe, or at least at the level of ripeness needed for whatever they will be used for.
Storage Options For Grapes
Grapes can be stored:
- In a climate-controlled area like a cellar for as long as 6 weeks. They will last longer if stored in dry cardboard boxes lined with straw or some other cushioning material.
- In the refrigerator’s crisper drawer for 3 to 4 weeks.
- In the freezer for up to 6 or 7 weeks at 32℉/0℃ without being damaged.
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