Grapes

Infobox on Grapes
Example of Grapes
Freshness facts
Optimum carrying temperature	-1,0°C to 0°C
Highest freezing point	-2,7°C
Acceptable product temp. at loading into containers	Max. 2°C above carrying temperature
Optimum humidity	90% to 95%
Ventilation setting for containers	0 m³/hr
Storage life	2-6 months, dependent upon variety
Climacteric / non-climacteric	Non-Climacteric
Ethylene production	Very Low
Ethylene sensitivity	Moderate
Modified / controlled atmosphere	1%-5% CO2; 2%-5% O2
Potential benefits	Increased CO2 - slight; reduced O2 - moderate
Availability
Australia/New Zealand South Africa South America	April - June December - June December - June

Grapes

Harvesting and handling

Grapes do not continue to ripen after harvest; they should be harvested at optimal maturity based on soluble solids content.

High consumer acceptance is attained for fruit with high SSC or SSC/TA ratio. Berry firmness is also an important factor for consumer acceptance as are lack of defects such as decay, cracked berries, stem browning, shriveling, sunburned or dried berries, and insect damage. Grapes (bunches) are mostly packed in 5-10 kg. cartons, often in retail carrying bags or punnets.

Cooling and storage

A temperature of approx. 0°C is generally recommended for storage of grapes, at which they have a storage potential of several months. The storage life is dependent on maturity at harvest, rapid pre-cooling, an effective fumigation programme and low constant storage temperature. Keeping quality is dependent upon variety, e.g. Thompson Seedless will keep for 2-3 months. Ribier keeps for 2-4 months, Alphonse Lavallée, Waltham Cross 3 months and Emperor 4-6 months.The shelf-life of grapes reduces by approx. 40% at +4°C and by approx. 70% at +8°C. Stem respiration rate is approximately 15 times higher than berry respiration.

Sweet berries may not freeze until -3°C, but their stems (containing much less sugar) can freeze at -2°C, leading to wilting and berry drop. To avoid the risk of freezing damage, the recommended carriage temperature is preferably to be around the freezing point rather than well below.

High relative humidity is necessary to minimise moisture loss (i.e. shrivelling of the berries) and maintain stems in good condition. Shrivelling and drying of the grapes may be prevented by packing the fruit in perforated polyethylene film inside the export cartons. The normal weight loss due to a reduction of moisture in the grapes is 2 - 3%.

One of the most common and obvious symptoms of deterioration results from the activity of bacteria and fungi. Attack by most organisms follows physical injury or physiological breakdown of the commodity. In a few cases, pathogens can infect apparently healthy tissues and become the primary cause of deterioration. In general, fruits and vegetables exhibit considerable resistance to potential pathogens during most of their postharvest life.

The onset of ripening in fruit and senescence in all commodities renders them susceptible to infection by pathogens.

Botrytis cinerea is the most common cause of spoilage. Grapes harvested after rain are much more prone to decay than those harvested after a dry period. The mould growth thrives at 24°C, but is still capable of growing and causing rot at temperatures of around 0°C. Botrytis infection can be reduced by removing desiccated, infected grapes of the previous season from vines, leaf-removal canopy management, pre-harvest fungicides, trimming visibly infected, split, cracked, or otherwise damaged grapes before packing, prompt cooling and fumigation with sulphur dioxide and/or use of continuous release SO₂ pads in combination with box liners.

Grapes deteriorate in storage through decay or natural ageing. When approaching the end of their storage life, the berries are losing their brightness and acquire a soft and flaccid texture.

Mixed loads

If grapes have SO₂ packets, they should not be mixed with other produce. The SO₂ can damage many kinds of produce. Otherwise grapes can be shipped in mixed loads. However, they should not be shipped with leaks, garlic, or onions to avoid odour transfer.

Cautions

O₂ below 1% can cause off-flavours. CO₂ greater than 15% may be used as a substitute for SO₂ treatment to control grey mould but after two weeks, it can cause browning of berries and stems. SO₂ is incompatible with CA so they should not be used together.

Storage disorders

Alternaria rot, Anthracnose, Aspergillus rot, Berry drop, Black mould, Blue mould, Botrytis cenerea, Cracking, Downy mildew, Grey mould rot, Powdery mildew, Rhizopus rot, Sour rot, Splitting, Sulphur dioxide injury.

¹ SSC = Soluble Solids Content; TA = Titratable Acidity

See also: http://www.ukpandi.com/fileadmin/uploads/uk-pi/LP%20Documents/LP_Bulletins/Chinese_Translations/Table%20grapes%20.pdf