8.7 PROCESSING SALMON CAVIAR
The technological steps involved in salmon caviar production were
discussed in previ-ous chapters. This chapter offers a condensed summary
of processing granular salmon caviar.
Salmon caviar is marketed as fresh (non-pasteurized), pasteurized
and chemically pre-served for both frozen and chilled storage, see
Figure 8-14. Smoking or artificial en-hancement of salmon caviar colour
or flavour is not popular. The steps involved in proc-essing salmon
caviar are given on Figure 8-13. Salmon caviar is processed predominantly
from fresh Chum and in part from Pink and other salmon ovaries at
the right maturity stage.
SALMON CAVIAR PROCESSING
After catch the fish is kept on ice or in refrigerated sea water
not longer than 48 hours. The fish are delivered right to the processing
site and ovaries are extracted and processed without delay. Fresh
and live fish are bled before the ovaries are extracted. Manual cut-ting
and ovary extraction is preferable to machine butchering, because
the essentially sterile ovaries can be carefully detached before total
cleaning of the belly cavity which may cause cross contamination.
Manual butchering ensures minimal contamination. Care must be taken
not to cut into the ovaries when splitting the belly, because it is
difficult to get rid of the broken egg membranes during the subsequent
technological steps.
If there is any delay (even for two hours) in processing, the extracted
eggs should be placed in cold storage. Ovaries are graded mainly by
freshness, because fish delivered from the same area are usually of
the same maturity. Ovaries are considered Grade No. 1 when they are
fully developed, firm, elastic, odourless, shiny and bright orange
or or-ange-red in colour. Sometimes one can observe local darkening
of colour of the posterior ovary tip or on the parts adjacent to the
backbone. If the darkening is not intensive the darker parts are torn
off and the ovaries still qualify for Grade No. 1. Vessels located
along the ovaries and filled with blood and pieces of kidney do not
discriminate against the ovaries being Grade No. 1. While screening,
the blood, blood clots or kidney pieces will drain off or be caught
by the slope screen. It is not recommended to use knives. Torn ovaries,
which have lost their intact shape because of rough handling could
also be con-sidered Grade No. 1 if this is the only defect. As ovaries
get darker in colour, soft, slimy and less elastic they are graded
out for No. 2 caviar or to be used for other than caviar products,
e.g. sujiko, bait. Failure to grade before screening contributes to
cross contami-nation, makes cleaning from membranes more difficult
and generally down grades the whole lot. Graded ovaries are quickly
rinsed and drained with ice cold water or light brine. Rinsing can
be done by dipping perforated baskets, partially filled with ovaries,
into a vessel with running cold water, which is constantly decanted
to get rid of impuri-ties. The use of ice cold water (1 to +5°C)
strengthens the membranes and makes screen-ing more efficient. If
ovaries are still not cold enough they are put into -2 to -3°C
cold brine (15% concentration) for 2-3 minutes.
Before screening the ovaries are drained and one by one manually
torn flat ('opened'). Ovaries are placed onto the first screen and
rubbed through by gently pushing the ovaries into the screen and simultaneously
performing circular movements with the palms of both hands. The whole
surface of the screen is used. Both rubber and cotton knitted gloves
are used. Soiled screens are replaced by clean ones as often as needed,
usually every 1 to 2 hours. Soiled screens are washed free of debris
in a specially designated area using high pressure water jets and
brushes.
The eggs run down a slope screen into a collecting basket with a
mesh bottom to drain off broken egg interior liquid. It is not recommended
to tap the screens in order to recover small lumps of eggs still connected
to tissues and stuck in the mesh screen. These lumps are collected
separate for bait processing before the screens are washed. Only eggs
which freely run off the screens are introduced into the batch.
Salting is done in saturated 100% brine at temperatures of 8-12°C.
Brine is prepared using salt of the highest grade. Brine is not used
more than twice. The egg/brine ratio should be at least 1:3. Salt
is added to the bottom of salting tanks to fortify the brine. The
added salt should be of larger particle size otherwise small particles
may be lifted due to agitation and stick to the eggs. This may result
in oversalting.
Usually mechanical agitators are used. Manual agitation by means
of a plastic paddle is used in small size operations. It is popular
to tennis racquets or similar metal mesh paddles to stir the eggs
manually while they are agitated in brine. This provides better mixing
and also serves to remove egg lumps, broken membranes and connective
tissues still remaining after screening. Netting frames, placed inside
and, attached to the salting tank serve the same purpose. Salting
time depends on the desired final target salinity. Usually salmon
caviars are salted to 3.5 - 4.0% salinity. The salting time to achieve
this salinity varies from 3 to 20 minutes. It depends on many factors
e.g. mature and fresh eggs should be salted for a longer time than
immature and marginally fresh ('soft') eggs. .Brine temperature and
egg/brine ratio also affects salting time.
Salting can be performed in two salting sessions. For about 50% of
the total salting time eggs are transferred to a tank containing clean
unused brine and the salting is resumed. This makes a clean product.
The second tank is then used for the next lot first salting ses-sion.
To determine what salting time is appropriate for any particular
lot is impossible without experimenting with small size batches which
model the actual conditions and measure sa-linity. The salting curve
i.e. salinity vs salting time, has a typical character. At the begin-ning
salinity is proportional to the salting time. At the end of the process
salt absorbtion slows down considerably. It is somewhere at the junction
of these two phenomenon that the right salinity and the best interior
yolky fluid viscosity are achieved. If the desired salinity is achieved
during the period when salinity is still rising proportionally to
time, watery cav-iar is produced. It may happen with immature and
soft eggs. That is why lower grade salmon eggs, are held in brine
longer to achieve the desired viscosity and become over-salted.
To measure salinity of one sample takes 2-3 minutes using conductometric
salimeters. Dis-tilled or plain water is added to a sample in the
ratio 9:1. After homogenizing and filtering (fine mesh or filter paper)
the filtrate is poured through the measuring column. The elec-trodes
should be kept clean and the instrument and kept rinsed after each
measurement. To estimate salinity by tasting is only an additional
test which aims to accumulate skill and understanding of the process.
When squeezed, properly salted eggs do not release the inner liquid
in the form of a jet but in the form of a honey like droplet. Other
indicators of when to stop salting are: the inner fluid does not have
blood colouring, and the salted dry eggs generate a rustling sound
when stirred in a bowl. When eggs are
squeezed in the palm of the hand they should not lump, but should
be easily detachable. Overdone eggs have a waxy mouthfeel. Agitation
is stopped 10-60 seconds before the salting time is over, so that
the heavier debris and broken membranes can settle to the bottom and
thus they are not scooped off.
Brine may be reused if filtered and fortified to 100% saturation.
Scooping is done with all kinds of plastic, metallic mesh or bamboo
baskets. It is important to get the eggs out as quickly as possible.
The eggs can first be put into a container and then redistributed
into draining baskets. Draining is done in two steps. The first time
draining lasts for a short time until the bulk of excessive brine
runs off. At that time it is very convenient to candle or inspect
the eggs and manually remove the remaining broken membranes using
tweezers. If salted eggs contain excessive broken eggs, lumps and
other impurities they could be screened through a clean screening
device for a second time. Simultaneously they will get dewatered from
excess brine.
When the salted egg mass is still wet it is easy to push it along
the flat and sloped sur-face of the inspection table by means of wide
spatulas. To make it easier to move the eggs, olive oil may be applied
to the surface. If the eggs are fairly dry they are ready to be packed
right away into bulk or institutional packages. If the eggs are too
moist they are left for additional draining-curing for several hours.
Leaving eggs overnight is widely practiced, but may result in overdrying.
Draining trays or baskets are placed on shelves in a separate clean
and air controlled room. Eggs are placed in layers not ex-ceeding
8-10 cm.
Mixing drained eggs with preservatives and oil can be done in low
revolution shaft and drum mixers, or manually on flat metallic surfaces
using spatulas. Chemical preserva-tives are diluted in minimal volumes
of light brine and sprayed on the eggs in amounts to meet the regulatory
restrictions for the final product, usually within 0.1%. To apply
preservatives in a powder form requires thorough mixing to avoid local
out-of-limit concentrations. After application, of the water soluble
preservatives a mixture of a vege-table oil (e.g. olive or corn oil)
and glycerol up to 0.6% can be added to prevent the eggs from sticking
together and to make them look shiny. Glycerol also adds a sweetish
after-taste to mask the slight natural bitterness of some eggs. The
use of oils and glycerol is popular in the Soviet Union.
When caviar is packed into containers care should be taken to achieve
a dense packing without air cavities. Before and during packing caviar
is constantly inspected and remaining impurities are manually removed.
This is done by gently compacting the eggs layer by layer. When machine
fillers are used the so called 'bottom-up' technique is used, i.e.
firstly the filling nozzle discharges the product onto the container
bottom and then moves up.
Bulk and institutional packages are often frozen and kept at -20°C.
Second grade eggs should not be frozen to avoid excessive release
of juice after thawing. Sufficient head-space should be provided to
ensure successful vacuum closure. Pasteurization in a water bath at
68°-70°C for 60-90 minutes adds to product shelflife. At all
times, pasteurized or not, caviar is best kept at -2 to +1°C.
Washing containers after packing, and especially after vacuum packing,
is mandatory to prevent microbiological build up on the container
surface and around the seal.
Frozen caviar is defrosted very slowly, if possible at 2°C per
day in order not to subject the eggs to the rigor of temperature changes
which may result in the release of excessive juice.
Pressed salmon caviar can be made from screened immature
and weak ovaries in a simi-lar way as was described for pressed sturgeon
caviar. However, this product, is processed extremely rarely. Salmon
caviar of different types is shown on Figure 8-14.
FIGURE 8-14: Salmonid Caviar
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