Matter other than grapes (MOG) - GWRDC

Current topics in this Winegrape
Assessment Series include:
Grower and winery
expectations in grape
production
Grape maturity
1. Total soluble solids, pH and
titratable acidity
2. Colour in red grape varieties
3. Cropping levels
Grape purity
1. Diseases - powdery mildew,
downy mildew, Botrytis and other
moulds and rots.
2. Agrochemical residues
3. Matter other than grapes (MOG)
4. Contamination
Grape condition
1. Uneven ripening
2. Temperature
3. Spoilage
4. Damaged berries
*Vitinotes in this series have
been sources from Winegrape
assessment in the vineyard and at
the winery, the 2003 WGCA-WFA
Liaison Committee report to the
Grape and Wine Research and
Development Corporation.
Viti-Notes
www.crcv.com.au 2005
What wineries want…..and why: Winegrape assessment in the vineyard and at the winery
G rape purity 3. Matter other than grapes (MO G )
Fungal diseases, agrochemical residue,
contaminants, any matter other than grapes (MOG)
and a mixture of varieties are detrimental in a load
of winegrapes, and while 100% purity can be
difficult to achieve it must be the aim of every
grower. Grapes are classified as food and therefore
have to comply with Food Standards for Australia
and New Zealand.
MOG includes all other vine material such as
petioles, leaves, canes and broken arms of vines. It
also includes foreign objects such as stones, picking
utensils, trellis parts, metal objects and irrigation
components. These are often difficult to detect in
loads until in the crusher, which can be damaged by
such inclusions, but it is highly variable as to how
much material or how big an object will cause
damage.
With expanded use of machine harvesting since the
late 1970s, MOG has become an issue as most
contaminants (other than chemicals) are directly
related to mechanisation, although, to a lesser
extent, MOG can also be present in hand-picked
loads. Machine harvesting technology has been
changing in recent years to greatly improve
harvesting techniques and to reduce the amount of
MOG. Improvement is still needed, however, and
often the skill of the harvester operator can play a
major role in the purity of the load.
Growers can also reduce the occurrence of MOG in
harvest loads by:
• Ensuring vine rows are clear of foreign objects.
• Controlling snails and other potential pests.
• Cleaning up vines after machine pruning to
remove potential MOG, eg. the brittle dead arms
caused by Eutypa.
What are the implications of not meeting specifications?
• Losses can occur through processing problems
caused by MOG, downtime for repairs to equipment,
and the cost of equipment replacement. In some
situations wineries have written into their grape
purchasing agreements that growers may be liable
for the cost of repairs if fault is established.
• MOG can be detrimental to grape quality
because of skin and berry damage, especially for
white varieties.
• Wine quality can be affected through too much
leaf in loads causing unwanted herbaceous
character. Excessive leaves in the load may also
increase the risk of agrochemical residue from
vineyard sprays.
• Excessive MOG means wineries are paying for
unwanted quantities waste which must be removed
at the crushing site.
What are some causes of not meeting specifications?
Common causes of problems are:
• Poorly set up machine harvester units.
• Absence of,or poorly maintained magnets on harvesters.
• Harvesting of vines late in the season when they
may be stressed and grapes are difficult to remove.
• Frost damage to vines resulting in dead shoots
that easily break off.
• Stressed vines in general, where leaves fall easily
and vine wood is often more brittle than normal.
• Harvesting in wet conditions where water weighs
down leaves and sticks and the harvester fans are
unable to remove them.
• Poor pruning techniques in the vineya r d ,
especially where hand clean-up following machine
pruning has been inadequate.
• Minimally pruned vines can increase the potential for
M O G, as there is a considerable amount of dry and dead
wood present where no pruning has occurred.

• Old vines that contain considerable amounts of dead wood
(possibly due to Eutypa or other trunk diseases).
• Poorly re-trellised vines that have not had the old wood removed.
• Objects left in the vineyard to mark posts and sprinkler heads not
removed prior to harvest.
• Failure to inspect bins and remove foreign objects prior to use.
How specifications are evaluated
TAKING SAMPLES
The MOG content of a load can be quantified by extracting and
weighing samples but this is inefficient, time-consuming and too
complicated to be a practical measurement tool, as sampling would
need to be representative of the entire load.
RATING
MOG-0
MOG-1
MOG-2
MOG-3
MOG-4
MOG-5
www.crcv.com.au
PERCENTAGE
MOG

Delivering grapes to specification
• It is Best Practice by the grower to deliver grapes at MOG-0 rating.
• Many grape purchasing agreements apply a minimum or
maximum tolerance - a measure for a specification above or below
which penalties generally apply, or grapes may be unacceptable
to the winery. Many wineries have a maximum tolerance for MOG -
generally this is MOG-2 rating. Deliver grapes within the tolerance
where a winery has written the specification to avoid penalties,
especially where it may affect pricing or rejection is a risk.
• The winery must notify growers of results which do not meet
specifications (within 2 hours is acceptable), to discuss the outcome.
The appropriate winery staff should also be contacted immediately as
load processing may be delayed.
THE CRC for Viticulture is a joint ve n t u re between the fo l l owing core participants,
working with a wide range of supporting partners.
Further information
1 This guide is out of print in its original format, but similar information
can be found in the publication Growing grapes to winery
specifications, available from Winetitles
Product or service information is provided to inform the viticulture
industry about available resources, and should not be interpreted as an
endorsement.
A useful reference is:
• Growing quality grapes to winery specifications, 2003,
edited by Sally Collings and available from Winetitles
• Research to Practice is a training program whose delivery can
be fine-tuned to suit each region. Enquiries to Peter Mansfieldon (08)
8222 9255 or visit www. c r c v.com.au/education/rtp/ for more
information.
Visit the web site at www.crcv.com.au/viticare/vitinotes/ for updates
and more Vitinote titles.
©2005 Cooperative Research Centre for Viticulture