5 Dehydration of otto Products Potato granules Potato granules are more usually commercially designated as Instant Potato or Potato Mash Powder. This product was first manufactured in the UK,on a commercial scale, some 55 years ago. As the name implies, precooked potatoes are dehydrated into granular form and, when hot water is added, they revert almost instantly to cooked mashed potato. This product has been widely developed as a convenience food in America and Europe, and is almost certainly the most popular form of dehydrated potato on the market today. It features extensively in snack foods There are several methods of producing granules but the generally accepted commercial method is the 'add-back process. Several improvements have been made in the manufacturing processes since World War Il, and some of these are referred to in british Patents No 683, 604(1952) and No 740, 711 (1955). The basic process goes back to, and is described in, earlier Patents-No, 496423. No, 525.043 and No. 601,152 The following description of the process explains the basic commerci add-back method but makes no reference in detail to the refinements and mprovements, introduced in recent times, by individual processors, many f which were originally patented
5 Dehydration of Potato Products Potato Granules Potato granules are more usually commercially designated as Instant Potato or Potato Mash Powder. This product was first manufactured in the UK, on a commercial scale, some 55 years ago. As the name implies, precooked potatoes are dehydrated into granular form and, when hot water is added, they revert almost instantly to cooked mashed potato. This product has been widely developed as a convenience food in America and Europe, and is almost certainly the most popular forin of dehydrated potato on the market today. It features extensively in snack foods. There are several methods of producing granules but the generally accepted commercial method is the 'add-back' process. Several improvements have been made in the manufacturing processes since World War 11, and some of these are referred to in British Patents No.683,604 (1952) and N0.740~711 (1955). The basic process goes back to, and is described in, earlier Patents - No.496,423, No.525,043 and N0.601~152. The following description of the process explains the basic commercial add-back method but makes no reference in detail to the refinements and improvements, introduced in recent times, by individual pmcessors, many of which were originally patented. I05
Flow Sheet Feed to Line Dry Cleaning Destoner washer Peeling Skin elimination Washing nspection- Trimming Slabbing(Slicing) Mashing-Mixing Add- Back mix Suppl Additives Granulating -Conditioning 1.5mr 65% add-back granules Secondary Drying(35%)by bulk Final Sieving through 250 micro Overtails return Primary Packing to mixer Flushing in poly-lined sacks
Flow Sheet Feed to Line I Dry Cleaning I Destoner Washer I Peeling I Skin Elimination I Washing I Inspection - Trimming I Slabbing (Slicing) I I Mashing - Mixing I Add - Back Mix I Sulphiting + Additives I Granulating - Conditioning I + 1.5mm rejected I to mixer by bulk Secondary Drying (35%) by bulk I Final Sieving through cooking kreeningd 65% add-back granules 250 micron sieve I 7 Overtails return Primary Packing to mixer Nitrogen Flushing I Secondary Packing in poly-lined sacks I06
A Lockwood self feed hopper in to which potatoes are being Varieties of Potato Suitable for granules The main requirements are(I)high solids content, (2) low reducing sugars,(3)freedom from aftercooking darkening, 4) immunity to wart diseases, and () shalloweyes In America and the UK, the preference is for white fleshed varieties, whereas in Western Europe, cream and yellow fleshed potatoes are more popular The following varieties are, therefore, in general commercial use for this process USA: Russet Burbank Katahdin Kennebec Cobbler ppewa
A Lockwood self feed hopper in to which potatoes are being tipped from a swivel head fork lift truck Varieties of Potato Suitable for Granules The main requirements are (1) high solids content, (2) low reducing sugars, (3) freedom from aftercooking darkening, (4) immunity to wart diseases, and (5) shallow eyes. In America and the UK, the preference is for white fleshed varieties, whereas in Western Europe, cream and yellow fleshed potatoes are more popular. The following varieties are, therefore, in general commercial use for this process. USA: Russet Burbank, Katahdin, Kennebec, Cobbler, Chippewa I07
Aran Comet, Aran pilot Home guard Estim Pentland Javelin, Pentland Crown Maris Peer, Cara Maris Piper, Pentland Dell, Europe: Bintje, Iris, Lenina (West and East)Record, Uren, Wilja, Desiree PROCESS ortant factor to be observed at all points of processing is Prevention of cell rupture in the raw material. Every individual cell that damaged in peeling, cooking, granulating or drying will release free starch, which will mitigate against satisfactory reconstitution, and will produce a sticky gelatinous mass instead of a light fluffy mashed potato Peeling should be by lye or the steam method, and the potatoes should be well sprayed with cold water afterwards. This can be done in a rod washer, or preferably in a brush washer as described in the chapter on preparation plant. Batch abrasive peelers are wasteful, and tend to create the very conditions of cell damage which should be avoided. More recently developed continuous abrasive peelers, with sophisticated control of the depth of peeling, may well meet the requirements of minimal cell damage, therefore the processor has a reasonably wide choice of equipment for this part of the process, but Flash Steam Peeling is preferred From the peeler and washing plant, the potatoes pass over an inspection belt where they are trimmed. With average quality raw material, ten women at the trimming belt should handle 16 tons in eight hours. At the end of the trimming and inspection table, the small to medium size potatoes o straight to the cooker whilst tubers of 44mm upwards are diverted to a slicing machine for slabbing into 20mm slices before returning to the main flow into the cooker. If required, the trimmed and sliced potatoes can be delivered into a surge tank prior to cooking; this has the effect of removing surface starch, and also provides buffer storage to keep the line running where there are breaks in the preceding pro ocess for some reason Cooking, in continuous cookers, may be in atmospheric steam for 45-60 min, or alternatively the potatoes may be partly cooked in hot water, cooled and then transferred to the steam cooker( Cording and willard method: 1955) From the cooker, which is usually a rectangular steam cabinet with a tainless steel mesh conveyor belt, the potatoes now emerge, thoroughly but not overcooked, and fall into a paddle mixer. This is normally of the U trough-type, with a rotating shaft fitted with T-shaped paddles at intervals
UK: Aran Comet, Aran Pilot, Home Guard, Estima, Pentland Javelin, Pentland Crown, Maris Peer, Cara, Maris Piper, Pentland Dell, (West and East) Record, Uren, Wilja, Desiree. Europe: Bintje, Iris, Lenino PROCESS The important factor to be observed at all points of processing is the prevention of cell rupture in the raw material. Every individual cell that is damaged in peeling, cooking, granulating or drying will release free starch, which will mitigate against satisfactory reconstitution, and will produce a sticky gelatinous mass instead of a light fluffy mashed potato. Peeling should be by lye or the steam method, and the potatoes should be well sprayed with cold water afterwards. This can be done in a rod washer, or preferably in a brush washer as described in the chapter on preparation plant. Batch abrasive peelers are wasteful, and tend to create the very conditions of cell damage which should be avoided. More recently developed continuous abrasive peelers, with sophisticated control of the depth of peeling, may well meet the requirements of minimal cell damage, therefore the processor has a reasonably wide choice of equipment for this part of the process, but Flash Steam Peeling is preferred. From the peeler and washing plant, the potatoes pass over an inspection belt where they are trimmed. With average quality raw material, ten women at the trimming belt should handle 16 tons in eight hours. At the end of the trimming and inspection table, the small to medium size potatoes go straight to the cooker, whilst tubers of 44mm upwards are diverted to a slicing machine for slabbing into 20mm slices before returning to the main flow into the cooker. If required, the trimmed and sliced potatoes can be delivered into a surge tank prior to cooking; this has the effect of removing surface starch, and also provides buffer storage to keep the line running where there are breaks in the preceding process for some reason or another. Cooking, in continuous cookers, may be in atmospheric steam for 45-60 min, or alternatively the potatoes may be partly cooked in hot water, cooled and then transferred to the steam cooker (Cording and Willard method: 1955). From the cooker, which is usually a rectangular steam cabinet with a stainless steel mesh conveyor belt, the potatoes now emerge, thoroughly but not overcooked, and fall into a paddle mixer. This is normally of the U trough-type, with a rotating shaft fitted with T-shaped paddles at intervals I08
along the length. The angle of the paddles to the line of the shaft is variable so that the flow of material can be accelerated or decelerated, as may be required, to thoroughly mix the product Mashing, and mixing in the add-back granules or'seed powder at this point must be gentle to avoid cell rupture, and the speed of the mixer is critical. The seed powder is continuously fed into the mixer at the point where the cooked potatoes enter, at a rate in excess, by weight, of the potatoes The average proportions might be 35 percent potato to 65 percent seed powder but this can only be established by practice, and will vary according to the solid matter in the raw potato, and, conversely, the moisture content of the seed. The ultimate objective is to obtain a blend with 35-40 percent moisture; the arrangement whereby the seed powder is available continuously at the mixer is described later The blend of cooked potato and add-back seed fills up the trough mixer, and is then allowed to fall over a weir, through an aperture in the end plate, into a second mixer of longer but shallower proportions. The purpose of this second mixer is to extend the mixing period, at the same time allowing the blend to cool as it travels along the trough. As stated before, the rate of travel is controlled by the of the paddles, and thor will take 25-35 min Sulphite and other additives, which may be required, are added to the blend by a suitable metering device, during the mixing Process No general rule can be applied as to the additives, as Food Laws differ from country to country, and the processor must familiarise himself with what is permitted, and what is not, in his own particular market. Additiv may include sodium metabisulphite, acid sodium pyrophosphate monostearates, anti-oxidants, flavourings and milk powde Sulphur Pyrophosphate, anti-oxidants, and sometimes milk powder are mixed with potato granules to make a ' master mix whereby the metering into the mash can be more accurately gauged and, by dilution, can be assimulated more evenly than small quantities of separate ingredient Glycerol monostearate in solution is metered in At the end of the second mixer, the blend again falls over a weir and passes to a conditioning bin, where the material cools to about 24"C in our wo bins are normally used, one being filled whilst the other is conditioning. This conditioning is a most important stage in the process, as it assists granulation and retrogradation of the starch From the bottom of the conditioning bin, the blend feeds into the first stage of drying. The primary dryer can be either (a)a pneumatic ring dryer, or(b)a thermal venturi dryer, both of which were described in Chapter IV a suitable feeding arrangement is required for the particular type of dryer
along the length. The angle of the paddles to the line of the shaft is variable, so that the flow of material can be accelerated or decelerated, as may be required, to thoroughly mix the product. Mashing, and mixing in the add-back granules or ‘seed’ powder at this point must be gentle to avoid cell rupture, and the speed of the mixer is critical. The seed powder is continuously fed into the mixer at the point where the cooked potatoes enter, at a rate in excess, by weight, of the potatoes. The average proportions might be 35 percent potato to 65 percent seed powder but this can only be established by practice, and will vary according to the solid matter in the raw potato, and, conversely the moisture content of the seed. The ultimate objective is to obtain a blend with 35-40 percent moisture; the arrangement whereby the seed powder is available continuously at the mixer is described later. The blend of cooked potato and add-back seed fills up the trough mixer, and is then allowed to fall over a weir, through an aperture in the endplate, into a second mixer of longer but shallower proportions. The purpose of this second mixer is to extend the mixing period, at the same time allowing the blend to cool as it travels along the trough. As stated before, the rate of travel is controlled by the angle of the paddles, and thorough granulation will take 25-35 min. Sulphite and other additives, which may be required, are added to the blend by a suitable metering device, during the mixing process. No general rule can be applied as to the additives, as Food Laws differ from country to country, and the processor must familiarise himself with what is permitted, and what is not, in his own particular market. Additives may include sodium metabisulphite, acid sodium pyrophosphate, monostearates, anti-oxidants, flavourings and milk powder. Sulphur Pyrophosphate, anti-oxidants, and sometimes milk powder are mixed with potato granules to make a ’master mix‘ whereby the metering into the mash can be more accurately gauged and, by dilution, can be assimulated more evenly than small quantities of separate ingredients. Glycerol monostearate in solution is metered in. At the end of the second mixer, the blend again falls over a weir and passes to a conditioning bin, where the material cools to about 24°C in an hour. Two bins are normally used, one being filled whilst the other is ‘conditioning’. This conditioning is a most important stage in the process, as it assists granulation and retrogradation of the starch. From the bottom of the conditioning bin, the blend feeds into the first stage of drying. The primary dryer can be either (a) a pneumatic ring dryer, or (b) a thermal venturi dryer, both of which were described in Chapter IV. A suitable feeding arrangement is required for the particular type of dryer I09
used but it is important that this should provide a consistent, regular rate of feed, compatible with the rate of throughput from the mixing plant, and proper balance must be achieved at this point. There must always be an adequate reserve of blend in the conditioning bins because, if the feed to the dryer is too fast or too slow, the whole system will break down DRYING The air velocity of the dryer must be carefully controlled from the outset, otherwise cell damage can occur here. The function of the primary dryer is to reduce, rapidly the 35-40 percent moisture in the blend to 12-l percent as the powder, which it now more correctly resembles, leaves the collectingcyclone. At this point, the powder is screened and coarse material Left: A Finex 22
used but it is important that this should provide a consistent, regular rate of feed, compatible with the rate of throughput from the mixing plant, and a proper balance must be achieved at this point. There must always be an adequate reserve of blend in the conditioning bins because, if the feed to the dryer is too fast or too slow, the whole system will break down. DRYING The air velocity of the dryer must be carefully controlled from the outset, otherwise cell damage can occur here. The function of the primary dryer is to reduce, rapidly the 35-40 percent moisture in the blend to 12-15 percent as the powder, which it now more correctly resembles, leaves the collecting cyclone. At this point, the powder is screened and coarse material Left: A Finex 22 sieving machine which is ideal for potato granules or vegetable powders l lO
this mesh, approximately two thirds is conveyed back by auger or bel sh plus 1. 5mm mesh-is removed. Of the finer material which asses eed powder to meet up with the cooked potatoes in the first mixing process The proportion fed back must be carefully metered to provide exactly the correct proportion in relation to the quantity of potatoes passing through the cooking stage. As explained before, this proportion will be of the order of 65 percent The remainder of the powder, having passed through the screen, passes to a secondary dryer, which ideally is(a)a fluidised bed dryer, or(b) a rotary louvre dryer. This secondary drying reduces the powder to 6-7 percent moisture content. The secondary dryer discharges into a collecting cyclone and it is customary to locate the latter in a cooling system. An air ring, similar in design to the ring dryer, but utilising cold air, is ideal for this purpose, and this cools the product down to about 16C. From the cold air cyclone, the powder discharges through a rotary valve on to a final screen fitted with a 250 micron stainless steel sieve, and the'through' material is the final product which then goes to pack-off.Any overtails from the final screening are returned back as seed. It is essential that a permanent cascade magnet be fitted on the outlet of the last screen,to remove any ferrous metal contamination. A Finex 22 sieve with 2 decks as illustrated is ideal for this purpose, and a Finex 48 sieve for the initial a3eono, rom the foregoing description, it is seen that the process involvesthe continuous feeding back of part of the dried material, which is used to sorb in excess of 50 percent of the initial water content of the cooked potato. The processor must therefore, always retain a stock of seed granules to start up the system at the beginning of a new season. It must also be remembered that the rate of pack-off of the final powder can only equate ith the input of raw potatoes, and if this is wrongly estimated, the seed will gradually bleed out of the system, and the process will eventually come to a halt. This balance can only be achieved with experience, and the constant attention of the dryer operative Product should be packed in nitrogen-flushed drums for prolonged storage, or 25kg polyethylene-lined sacks for 6-8 weeks storage in temperate conditions RATIO Expected ratio of final product at 6 percent moisture content, using potatoes with 20 percent solids, would be expressed as about 6: 1
- plus 1.5mm mesh - is removed. Of the finer material which passes through this mesh, approximately two thirds is conveyed back by auger or belt as seed powder to meet up with the cooked potatoes in the first mixing process. The proportion fed back must be carefully metered to provide exactly the comt proportion in relation to the quantity of potatoes passing through the cooking stage. As explained before, this proportion will be of the order of 65 percent. The remainder of the powder, having passed through the screen, now passes to a secondary dryer, which ideally is (a) a fluidised bed dryer, or (b) a rotary louvre dryer. This secondary drying reduces the powder to 6-7 percent moisture content. The secondary dryer discharges into a collecting cyclone and it is customary to locate the latter in a cooling system. An air ring, similar in design to the ring dryer, but utilising cold air, is ideal for this purpose, and this cools the product down to about 16°C. From the cold air cyclone, the powder discharges through a rotary valve on to a final screen fitted with a 250 micron stainless steel sieve, and the 'through' material is the final product which then goes to pack-off. Any overtails from the final screening are returned back as seed. It is essential that a permanent cascade magnet be fitted on the outlet of the last screen, to remove any ferrous metal contamination. A Finex 22 sieve with 2 decks as illustrated is ideal for this purpose, and a Finex 48 sieve for the initial screening. From the foregoing description, it is seen that the process involves the continuous feeding back of part of the dried material, which is used to absorb in excess of 50 percent of the initial water content of the cooked potato. The processor must therefore, always retain a stock of seed granules to start up the system at the beginning of a new season. It must also be remembered that the rate of pack-off of the final powder can only equate with the input of raw potatoes, and if this is wrongly estimated, the seed will gradually bleed out of the system, and the process will eventually come to a halt. This balance can only be achieved with experience, and the constant attention of the dryer operative. Product should be packed in nitrogen-flushed drums for prolonged storage, or 25kg polyethylene-lined sacks for 6-8 weeks storage in temperate conditions. RAT1 0 Expected ratio of final product at 6 percent moisture content, using potatoes with 20 percent solids, would be expressed as about 6:l. 111
ingle drum dryer for potato flakes(courtesy of Mitchell Dryers Ltd) POTATO FLAKES Flow sheet Feed to Line Dry Cleaning Peeling Skin elimination Washing Inspection-Trimming Slabbing (Slicing) Hot Water Cooking Steam Cooking
Single drum dyer for potatofldkes (courtesy ofMitchell Dryers Ltd) POTATO FLAKES Flow Sheet Feed to Line I Dry Cleaning I Destoner-Washer I Peeling I Skin Elimination I Washing I Inspection-Trimming I Slabbing (Slicing) I Hot Water Cooking I I Steam Cooking Cooling
cIng Additive addition Drying Flake Breaking Inspection Antioxidant addition or Primary Packing <Antioxid nt addition or Nitrogen Flushing econdary Packing in poly-lined sacks of the Agricultural Research Service in Philadelphia, US! opmey Cording The production of Potato Flakes was developed in 1954 and willard at the eastern utilisation Research and Deve Potato flour had been produced on single drum dryers for at least 70 years but it was not until 1954 that the technique was perfected, whereby the drum dryer could be used to produce a product, which, on reconstitution with hot water, gave a mash equal in texture and appearance to freshly mashed potato The success of the process lay in minimising the rupturing of the starch cells, and the special steps, taken in precooking and cooling,to retrograde or reduce the solubility of the amylose fraction of the potato starch. (See Potato Granules cooking method) Varieties of Potato Suitable for Potato Flak The required characteristics are similar to those for granules, therefore all the varieties listed for the latter product are suitable for flaking Process Peeling is by lye or steam methods as a general rule, followed by a thorough brush washing and cold water spraying to remove surface starch After inspection and trimming, which must be very thorough, so as to remove all eyes and blemishes, sizing and slabbing follows, as for granule
I Ricing I Additive Addition I I Flake Breaking I Inspection I Antioxidant addition or I I Nitrogen Flushing I Secondary Packing in poly-lined sacks Drying Antioxidant addition or Primary Packkg (Nitrogen Flushing The production of Potato Flakes was developed in 1954 by Cording and Willard at the Eastern Utilisation Research and Development Division of the Agricultural Research Service in Philadelphia, USA. Potato flour had been produced on single drum dryers for at least 70 years but it was not until 1954 that the technique was perfected, whereby the drum dryer could be used to produce a product, which, on reconstitution with hot water, gave a mash equal in texture and appearance to freshly mashed potato. The success of the process lay in minimising the rupturing of the starch cells, and the special steps, taken in precooking and cooling, to retmgrade or reduce the solubility of the amylose fraction of the potato starch. (See Potato Granules cooking method.) Varieties of Potato Suitable for Potato Flakes The required characteristics are similar to those for granules, therefore all the varieties listed for the latter product are suitable for flaking. Process Peeling is by lye or steam methods as a general rule, followed by a thorough brush washing and cold water spraying to remove surface starch. After inspection and trimming, which must be very thorough, so as to remove all eyes and blemishes, sizing and slabbing follows, as for granule I13
production. The cooking procedure is most important, and this is the main part of the process as set out by Cording and willard The first stage is precooking in hot water, and for this purpose, continuous auger-type cooker is often employed. The dwell time is about 30 min at 71oC Coolingtakes place in a similarvessel, circulating cold water to sustain a temperature of 10oC for 20-30 min Section of the Erin Foods plant at Mallow, Eirepotato flake process showing Gouda roller dryer The potatoes then pass to a continuous atmospheric steam cooker with a cycle of 35-50 min. Overcooking destroys texture, and this must be carefully controlled. High solids potatoes require less cooking than low solids varieties Ricing, or mashing, follows the cooking process. This is achieved by feeding the cooked potatoes through rolls into a rotatbg cylinder, perforated with 6mm holes. The cooked slices are gently forced through the perforations, and a ribbon screwon the inside of the cylinder discharges the product at one end. This equipment was designed in the Us but there are equally acceptable alternative methods in Europe Additives are introduced after ricing to improve stability, texture and colour. As in the case of granules, these may comprise sulphite, glycerol monostearate, sodium pyrophosphate, citric acid, etc. Sometimes anti oxidants are also used but legal restrictions on their use apply in some countries. Skimmed milk powder is used in small quantities by some manufacturers
production. The cooking procedure is most important, and this is the main part of the process as set out by Cording and Willard. The first stage is precooking in hot water, and for this purpose, a continuous auger-type cooker is often employed. The dwell time is about 30 min at 71 °C. Cooling takes place in a similar vessel, circulating cold water to sustain a temperature of 10°Cfor 20-30 min. Section of the Erin Foods plant at Mallow, Eire - potato flake process showing Gouda roller dryer The potatoes then pass to a continuous atmospheric steam cooker with a cycle of 35-50 min. Overcooking destroys texture, and this must be carefully controlled. High solids potatoes require less cooking than low solids varieties. Ricing, or mashing, follows the cooking process. This is achieved by feeding the cooked potatoes through rolls into a rotatbg cylinder, perforated with 6mm holes. The cooked slices are gently forced through the perforations, and a ribbon screw on the inside of the cylinder discharges the product at one end. This equipment was designed in the US but there are equally acceptable alternative methods in Europe. Additives are introduced after ricing to improve stability, texture and colour. As in the case of granules, these may comprise sulphite, glycerol monostearate, sodium pyrosphosphate, citric acid, etc. Sometimes antioxidants are also used but legal restrictions on their use apply in some countries. Skimmed milk powder is used in small quantities by some manufacturers. l l4
