9. Agriculture, Nutrition and Food Supply

Agriculture onboard DL4 must provide the residents with their nutritional requirements but also supply a sufficiently varied and interesting diet to prevent boredom with the available food.  However, these two aspects must be catered for in a limited amount of space.

Unfortunately, as DL4 will only house 10,000 people within such a comparatively (to Earth) small space, the atmosphere will not supply a large enough ‘buffer zone’ for the life support systems to cater for ruminant cattle herds.  Also, within a CELSS (Closed Environment Life Support System), where life support systems depend on plant photosynthesis, the inclusion of large fields of hay will not be acceptable from an atmospheric or land area point of view.  Unlike most of the materials used in the construction of DaedalusaL4, cows cannot be brought from the Moon and therefore, transportation of live cattle from Earth would prove not only costly but also, probably, controversial.  The low energy efficiencies of poultry and rabbit consumption will limit the use of these animals as food sources onboard, however this does not necessarily rule their use out, as individuals may wish to farm, for instance, an individual chicken coup – though the following food supply plan should render this option unnecessary as vegan alternatives are presented.  In terms of energy efficiencies, animal farming is unacceptable for a CELSS, as rates can vary from as low as 2.3% to 2.9% for lamb and beef, to a maximum of 19% for turkey (ref. 37).  Fish could easily be accommodated within the ‘natural’ waterways (see 10 Recreation) onboard DL4 but no industrial scale operation is planned for their harvesting and this can once again be an individual preference. Hence, vegetarian/vegan diets were chosen as the main food source of the settlement.

To deal with the remaining issues of food supply (once meat production had been ruled out) the following areas were defined:

1.       Type of Agriculture

2.       Crops to be Grown

3.       Layout of Agricultural Area

4.       Food Processing Methods

9.1        Type of Agriculture

As plant purification of hygiene (gray) water is an essential part of DL4’s life support systems, the use of hydroponics becomes attractive as the main agricultural method onboard the station.  This would then only require the circulation of dirty water from the residents’ washing facilities and Biological Decomposition and perhaps VAPCAR (Vapour Phase Catalytic Ammonia Removal) and SCWO (Super Critical Wet Oxidation) (see 17 Life Support Systems) into the agricultural area with limited filtering (if any) before minerals are directly returned to the plants.  Three main problems arise from this method of plant production. 

Firstly, some plants necessary for the settlement’s residents have proven difficult or impossible to grow under the conditions supplied by hydroponics.  The main examples (of the plants to be grown in large amounts on DL4) are white potatoes and carrots, which require a solid growing medium to undergo tuberization, and peanut plants, which require a solid medium as the nuts that initially form in flowers eventually push themselves into the ground as they mature.  Devoting a small section of agricultural area to solid medium products easily solves this problem. However, supplying the solid medium with adequate nutrients poses an additional obstacle to the production of these crops.  Fig. 9.1a details the method for both recirculating water to the plants as well as supplying them with the necessary nutrients from the hygiene water (nutrient solution reservoir).  [A similar method will be used for supply of nutrients to the hydroponics sections.]

Secondly, another difficulty that is easily overcome, perennial plants, whose growth using hydroponics has been studied, tend to stop flowering after three or four life cycles.  However, this should not significantly affect agricultural methods onboard DL4 as most of the plants used for food supply, and thus nourished by hydroponics, are grown from seed on a year to year basis while most perennial flowering plants will be used within the human habitat for decorative purposes (although we have integrated this function with usability – see 10.4 Recreation), and will therefore be grown in a solid medium.  Any perennial flowering plants (i.e. - Strawberries) used within the agricultural system will simply be regrown from seed or seedling when and if flowering fails to take place.

The final main problem is not so easily overcome.  Due to the nature of the water recycling methods within DL4’s life support systems, shower water, containing dissolved cleaning chemicals (soap), is directly fed to the hydroponics systems.  However, soap’s traditional chemical base is sodium.  This element serves no major purpose for most plants and thus it is not absorbed from the liquid root matrix, instead building up and sticking to the roots of the plants, eventually hindering the transfer of necessary minerals from the hygiene water to the plants.  This problem will be solved by using a potassium (an element readily absorbed and required by plants) based soap in the residents’ hygiene facilities (ref. 34).

However, as urine (which contains 90% of all sodium taken in to the body) will, after pre-processing in VAPCAR (see 17.1 Urine Processing), be passing through the plant nutrient delivery system, a specific cycle of plants must be implemented through which the nutrient rich hygiene water passes before flowing to those plants that are incapable of processing sodium.  These ‘initial’ plants will be the salad crops, such as Beetroot (Table beet) and Spinach, and Seaweed.  These crops should provide the medium for the successful recycling of Na back to the human diet.

Despite these problems and the necessity of extra equipment (for monitoring and control) hydroponics, in the main, provides the most effective plant growth method available.  Its use helps prevent potential problems with microbial contamination of agricultural soil, lowers the cost of transport (as water can be shipped from the Moon), and with the provision of pumps to properly aerate the liquid matrix, decrease the inedible plant yield by lowering the percentage mass of root per plant from 30 or 40% to 3 or 4% (this advantage only breaks down with some tuber plants like those detailed above, ref. 18).  Within the solid medium agriculture and recreational plant sections such aeration and humification will be provided for by the earthworm.

Across the settlement, but specifically in the agricultural sections, bees will be used for pollination.  Various species were thought of, however, both the Bumble bee and the Buckfast bee are known for their docile nature and thus are not prone to stinging.  The Bumble bee requires an underground hive (self-constructed), which rules it out of exclusive activities in the hydroponics area, while the Buckfast bee will require a provided hive and thus offers the additional advantage of easily collected honey (not available from the Bumble bee).

Problems however arise with the segmentation of the different areas of the settlement as the bees will require easy access between different plants.  Within the ‘recreational plants’ this will be easy to achieve but some method of access will have to be designed between the various climates of the hydroponics section.  Therefore, a certain amount of artificial pollination will have to take place where access can not easily be provided (e.g. – Soy beans, see below) although this should be kept to a minimum.

Sufficient lighting should be provided from the sun through the lead glass windows for plants grown in the human habitats.  This may be slightly deficient in UV light, due to the nature of the transparent lead, however small amounts of UV light will be supplied, as necessary for proper plant growth but more specifically, within safe limits, for the humans.  This is needed for the body to produce Calciferol (Vitamin D) under the skin as vegan sources of it are scarce.  For the majority of plants that are not supplied with ‘natural’ daylight periods, for proper growth, by DaedalusaL4’s mirror or as they are in a specific day/night section of the agricultural area, the addition of Red LEDs (Light Emitting Diodes) plus 10% Blue Fluorescent lights will provide a low energy alternative to daylight (ref. 16).

9.2        Crops to be Grown

The question of what crops should be grown on DL4 posed serious difficulties.  The plants grown must produce acceptable amounts of food per unit area, in order to ensure a constant supply, but this factor must not limit the variety of foodstuffs available for consumption.  The chosen plants must also provide for all the nutritional requirements of the residents.

On the basis of the above requirements, a primary list of constantly required crops was formulated.  The plants in this list should take up most of the agricultural facilities (although some of the plants are less important than others, i.e. - herbs) while other, less nutritionally important crops, are grown on a smaller scale depending on preference/demand of the residents and conditions at the time.  The primary list provides types of plants to be grown, however a few varieties of these will be grown in order to prevent boredom and maximise nutrition.  Some varieties of particular note, for their taste and adaptability, are listed briefly (in parenthesis).  Such examples are just that and only show the huge range of options that still exists even within this crop list.  [Note: this list does not contain those flowering plants or trees to be grown for ‘recreation’ and possible harvesting in the human habitats].

Primary Crop List:

Acorn Squash; Apple; Aubergine; Banana Squash; Barley; Beetroot – ‘Table beet’; Blackberries; Blackcurrants, Broccoli (Super Dome, Minaret, Green Comet, Purple Sprouting); Butternut squash; Cabbage; Carrots; Cauliflower; Chickpea; Chillies; Chives; Courgette; Corn; Cotton; Cowpea – ‘Black/Yellow-Eyed Pea’; Cucumber (Lemon, Amira, Orient Express, Vert de Massy, De Bouenil); Fennel; Flax; Garden peas; Garlic; Ginger; Grapefruit; Grapes; Hops; Horseradish; Hubbard Squash; Kale (Winterbor, Ornamental); Lemon; Lentil; Lettuce (Arctic King, Brune d’Hiver, North Pole, Rougette du Midi, Rouge d’Hiver, Winter Density, Winter Marvel); Maize; Melon (Cantaloupe, Persian, Santa Claus, Casaba, Crenshaw, Honeydew – Earlidew, Watermelon); Millets; Mint; Mushrooms; Nectarines; Oats; Onions; Orange; Oregano; Parsley; Peaches; Peanut; Pear; Pepper – sweet; Peppercorn; Pinto beans; Plums; Potato (Huckleberry, Blossom, Yukon Gold, Russet Burbank, White Rose, Round White, Round Red); Pumpkin; Quinoa; Radish; Rape seed –  Canola; Raspberries; Rice; Rye; Sage; Seaweed; Sesame; Snow peas; Sorghum; Soybean; Spinach; Strawberry; Sugar beet; Sunflower; Sweet potato; Swiss chard; Thyme; Tomatillo; Tomato (Sun Gold, White Wonder, Evergreen, Costoluto, Genovese, Big Rainbow, San Marzano); Turmeric; Turnips; Watercress; Wheat.

Some of the crops of particular note include (ref. 2, 5, 10, 16, 28, 33, 46, 47, 48, 49):

Oats, which provide high protein levels using a broad range of amino acids, are a fine example of a grain that could easily be grown extremely effectively under the correct controlled conditions.  For instance, using hydroponics, and optimum CO2 levels (@ 1,200ppm), wheat can be grown to give 60gm-2day-1 of edible plant mass, allowing a dense culture of up to 2000 plants m-2.  Wheat provides an excellent source of Thiamine (Vitamin B1), Niacin (Vitamin B) and magnesium, specifically from wheatgerm and wheat bran, so its production on such an efficient scale would prove beneficial.  Maize’s height may cause problems with such a dense growing strategy however this is outweighed by it’s advantages as both a familiar cereal grain and the amounts of Tocopherol (Vitamin E) that can be consumed through its oil.

Rice is highly nutritious and provides an excellent example of a crop for growing under hydroponics (although this is not necessary for its growth as it is primarily grown in paddy fields for weed control).  Quinoa is a highly nutritious South American grain and has provided a staple crop in Peru and Chile for many years.  Sorghum is very nutritional although rarely eaten as a food crop in the United States (unlike the rest of the world).  On DL4 its grain can either be used conventionally or refined to produce sorghum molasses, containing iron, calcium and phosphorus.

Whilst avoiding boredom with crops and monocultures (which could increase risk of crop failures) careful selection of suitable varieties of grain (specifically wheat) should be considered as these can dramatically change the amount of edible yield (flour etc.) available from the grain.  They also influence the amounts of gluten (an elastic cereal protein) contained in the crop.  Gluten can be separated in varying degrees from flour in order to produce different bakery products while the gluten itself is very useful as a meat analogue (specifically pork, chicken or beef) much like soy bean tempeh (discussed later).  Starch is also removed (with the gluten) and this can be used as a thickener in drinks and sauces.

Unlike the white potato (previously mentioned), the sweet potato can be grown with high yields in artificial conditions using hydroponics.  This is important, as the sweet potato is more nutritious and flavourful than the white potato and therefore can be grown in greater quantities.  This will allow the required solid medium space to vary slightly depending on demand for the white potato, which is more familiar to northern cultures.  Both types of potatoes will provide a necessary source of potassium (K), carbohydrates, Vitamin C and minerals.  The white is also high in Vitamin B6 while the sweet contains Vitamin A.  Both Sugar beet and Beetroot (Table beet) could be grown not only for their swollen roots but also for their leaves.  Sugar beet would obviously also provide a ‘popular’ source of sugar and as an edible by-product another type of molasses.

Green vegetables (Broccoli, Cabbage, Garden peas, Kale, Lettuce, Snow peas, Spinach and Swiss chard) should be easy to grow using hydroponics.  They provide excellent sources of Ascorbic acid (Vitamin C) and Phylloquinone (Vitamin K) while also supplying most of the required mineral micro-elements such as zinc (Zn), copper (Cu), iodine (I), manganese (Mn), chromium (Cr) and cobalt (Co) and the macro-element magnesium (Mg).  With the exception of Lettuce they also act as good sources of calories.  Spinach will be grown as an excellent source of calcium (100g of Spinach more than covers the recommended daily intake) and Vitamin C.

Swiss chard provides Vitamins A and C as well as iron, however its main advantage is variety.  Its greens can be cooked like spinach while the stalks may be served like asparagus.  Chard is also a member of the cruciferous vegetables (broccoli, cabbage, cauliflower, kale, mustard greens, and turnips), which are thought to help prevent cancer due to their high levels of antioxidants, specifically Beta Carotene (which offers the advantage of being convertible to Vitamin A but is also easily expelled if Retinol – Vitamin A – levels become toxic).  Another cruciferous vegetable, Kale, a cabbage like plant, provides ample amounts of Vitamins A and C, Folic acid, calcium and iron.

Using hydroponics, special growth support systems will be required for plants such as Cucumber, the various Squashes, and Pumpkin as their vines must be controlled.  However, they will provide good sources of minerals as well as calories.  Carrots, mentioned previously as requiring a solid medium, will provide an excellent source of Retinol.

Rape seed and Sunflower were principally chosen for their oils.  These are required to supplement the low fat vegetarian diets.  However, extraction may not be necessary as Sunflower seeds provide a suitable salad item and much like Peanuts could provide the required lipids through direct consumption (this option was chosen by the residents of Biosphere 2).  Peanuts will provide an excellent source of Folic acid for the residents and were previously mentioned as a potential problem - requiring a solid medium for growth.  Sesame will also be grown for its seed and its oil, both of which provide excellent sources of calcium.  Sesame oil can be used as an alternative cooking oil (especially frying, as it has a smoke point of 216°C) and as a salad dressing.

Soybeans will play an important part in DL4’s agricultural section.  Its food products are numerous and it can also be put to use in non-food applications such as biodegradable plastics.  Hence, its main advantage is a high protein content with up to 39% in terrestrial based plants (this should increase with the already mentioned decrease in root mass).  It can be used to produce soybean oil, which is high in both polyunsaturated fats and monounsaturated fats and low in saturated fats making it a healthy cooking oil and also a useful ingredient in the manufacture of margarine.

Other useful products include soy milk, which can provide a high protein alternative to cow’s milk on DL4.  This is high in iron with no cholesterol but unfortunately low in sodium and calcium.  While a vegan diet usually provides adequate sodium through salad crops (mentioned previously) to replenish the body’s supply (as it is naturally recycled in the kidneys’ nephrons, along with chlorine) the calcium deficiency, caused by a lack of dairy produce, must be supplemented by green vegetables, specifically Cabbage (as well as Spinach and Sesame – mentioned earlier), and Onions (now believed to contain more calcium per unit mass than milk).  On DaedalusaL4, there will be no renewable source of salt (such as Table Salt - NaCl), therefore unless the compound is imported from Earth, people will have to adapt to the healthier low salt diet provided.  However, seaweeds onboard could provide a salty taste if dehydrated, powdered and sprinkled on food.  This diet also provides no specific sulphur rich foodstuff, however the problem of a sulphur deficiency should not arise as normal food intake will cover the loss forced by a lack of dairy products.

Soy milk will also provide us with the crop’s main vegetarian product – tofu.  This is produced from curdled soy milk and is also low in calories and sodium while high in protein.  Tofu can be used in soups, stir fries, casseroles, salads, sandwiches, salad dressings and sauces and the ability to store (for three months frozen) will allow a constant supply to the residents.

Another common product of soy beans are soy sauces and tamari, which are used to flavour dishes – an extremely important supplement on DaedalusaL4 to prevent boredom with limited crops.  The less heard of Miso is a paste produced from soybeans that can be used as a spread or dip with the consistency and texture of peanut butter.  Miso will provide one of the only supplies of Vitamin B12 for the residents along with proteins.  It also has the additional advantage of several flavours, supplied by cultivating the paste in either a barley, rice or plain soybean base.

The final major, more surprising product, of this versatile plant is soy flour (kinako).  This, unlike the primary grain flours, is very high in protein (twice that of wheat flour) and low in carbohydrates.  This powder supplies a high calcium variant to be mixed with the standard flours maintaining interest in the more traditional foods.

One note about soy beans production: it may be necessary to coat the planted seed with nitrogen fixing bacteria (e.g. Rhizobium) when using hydroponics due to the extreme amounts of nitrogen the plant requires to produce such high protein contents.  This would supplement the nitrogen recycling system (see 17 Life Support) but might cause difficulties if the ‘free’ bacteria were to alter the nitrogen balance and get out of control.  For this reason, if the practise of ‘legume bacteria coating’ takes place, soybeans should be contained separately to the other plants in case of difficulties.

Other legumes of particular note are the Chickpea, Lentil and Pinto Bean.  Chickpeas are widely used in the Mediterranean to produce textured dishes such as hummus and couscous.  Lentil’s provide calcium, Vitamins A and B and are a good source of iron and phosphorus. Pinto Beans provide the main ingredient for such exciting dishes as Refried Beans and Chile con ‘TVP’ (Textured Vegetable Protein = Carne analogue)!

Fruits will supply supplementary minerals (specifically potassium) and vitamins necessary to stay in good health and will add important variety to the residents’ diets.  Certain crops are suited to hydroponics like Blackcurrants (rich in Ascorbic acid – Vitamin C), Strawberries (iron, potassium and Vitamin C) and Raspberries (iron, potassium and Vitamins A and C), while others may need certain adaptations.

The Tomato (which is rich in Vitamin C and contains appreciable amounts of Vitamins A and B, potassium, iron, phosphorus, and fibre), Melon (of which two broad varieties are available – the Watermelon and the Muskmelon) and Tomatillo (which is rich in Vitamins A and C) crops must be accommodated within the vine infrastructure mentioned earlier in reference to the Cucumber.  Of the two varieties of Melon, the Muskmelon is slightly more nutritious (the Cantaloupe is an excellent source of Vitamins A and C while the Honeydew provides good quantities of Vitamin C).  However, Watermelons (still containing a fair amount of Vitamins A and C) are slightly more familiar to North Americans.  Hence, a situation of supply and demand arises with production of different Melon types possibly varying with time.

Apples (Vitamins A and C) and Pears (phosphorus and Vitamin A) are unsuited to hydroponics, as they grow on trees.  However, these could be grown within specific areas of the human habitat to provide a sense of perspective and reduce claustrophobia along with other fruit bearing trees, like Orange and Lemon (both excellent sources of Vitamin C and the Lemon also provides calcium).  The climate of the human habitat should provide suitable conditions so long as irrigation is provided.  Another option for plants in recreational areas is the provision of berry shrubs, such as Blackberries, for people to pick themselves throughout the recreational areas of the Human habitat.

Condiments, such as Fennel, Sweet peppers and Chillies, and herbs, such as Tumeric, Sage and Parsley, add little nutritionally (although Fennel is rich in Vitamin A and contains a fair amount of calcium, phosphorus and potassium) to the crop list, however will be essential in maintaining interest in the food supplied on DaedalusaL4.  Additional small plants, like these, will also be grown on a small basis within the human habitat (see 10.4 Recreation).

The last noteworthy food crop, to be mentioned here, is Seaweed.  This is available in numerous varieties (Kombu, Laver, Wakame, Nori and Carrageen – most familiar to our Irish team) and can be grown to produce soups, vegetables, tea, sushi and seasoning.  Already mentioned as a source of sodium it also provides a rich source of iodine (which will be particularly important to children and those not partaking of any salt water fish).  Its most useful purpose onboard will be, once dried to form Agar, as a setting agent and its content of Alginic acid can also be used as a stabiliser and thickener.

One borderline crop required for food supply will be yeast.  This fungus will be cultivated in order to raise doughs such as bread (Baker’s Yeast), in combination with a grain flour, and to produce alcohol (Brewer’s Yeast), in combination with Maize (Corn) or Rye (flavoured with Hops) to produce Beer and Grapes for wine production.  All plant crops used in alcohol production are also useful for other purposes – Hops produces hop shoots that can be served like Asparagus, Rye can be refined to a dense flour to add flavour to breads, while Barley can be used as a base for Miso – therefore brewing will, in effect, be a side industry.  Yeast will also supply an excellent source of iron, potassium, Folic acid and Vitamins B3, B6 and B12 in normal foodstuffs.

On DL4, there will be one exception to the strict plant regime described above.  The farming of snails will provide an interesting supplement to an otherwise vegan diet, although perhaps not palatable to all cultures onboard.  The Vineyard (or Burgundy) Snail, considered the best for eating, could provide a use for the large amounts of grape leaves produced through the cultivation of Grapes.  Other types of snails are also available (petit-gris) to add variety to the diet.

Two non-food crops included in the primary agricultural list are Cotton and Flax.  These will be used to produce clothing for the residents – Flax is used to manufacture Linen – and are covered in 11.5, Goods for Residents’ Use.

9.3        Agricultural Area Layout

As the agricultural area of DL4 will be used additionally for the purposes of Life Support (Carbon Dioxide Removal, Oxygen Generation and Water Processing) a floor area must be chosen that satisfies the needs of these recycling loops as well as providing sufficient harvests to feed the residents.  On this basis, given certain crop densities and quantities of crops in season, a total area of 869,200m2 was chosen for agriculture.  This will be double stacked requiring a floor area of 434,600m2 (for details of calculations see 17.7 Oxygen Generation).

For the purposes of Life Support, the overall agricultural area will be initially divided in two (not geographically, for geographical divisions see 7 Internal Design) to provide a constant oxygen generation system.  These divisions will be further segmented into four and the growth of each will be stunted to provide a season imitation so that most crops can be produced year round (see 17.7 Oxygen Generation).

However, crops will have to be further segmented within these ‘seasons’ to allow for different climates.  For this purpose the daylight and temperature requirements of our main crops were considered and seven broad climates chosen.  More climates can be used within the agricultural section (which will be easily segmented due to its low ceiling height of 5 to 6m) but these examples represent the largest areas that will incorporate most crops.

Firstly, a ten to fourteen hour daylight time will be ‘created’ with three temperature zones.  The first, between 15 and 20°C, to accommodate plants such as the Strawberry and the Potato, the second between 20 and 25°C, to house legumes such as the Soybean, and the third, between 25 and 30°C, for plants like Rice and Peanuts.  Another ‘time zone’ with fourteen to eighteen hours of daylight (per twenty four hours) will contain a further three temperature zones.  These will house, in the 15 to 20°C segment, plants such as Kale; in the 20 to 25°C section, plants like Lettuce, Melon, Spinach and Tomato; and, in the 25 to 30°C division, plants similar to the Sweet Potato.  The final day-length variation will conform to a 18 to 24 hour day.  Although only containing one temperature variation (between 15 and 20°C), this section will be vital as it will be the principal grain producing area with particular emphasis on Wheat (ref. 16).

9.4        Food Processing Methods

Food processing equipment onboard DL4 must be capable of not only producing a broad spectrum of foods from one crop but also be able to process several crops in order to minimise space requirement and lower the mass of materials used to construct this equipment.  Therefore the processes that will be necessary to produce a reasonable selection of food (e.g. - fermentation, boiling, gelatinisation), en mass, were selected and on the basis of these, suitable equipment was chosen.  This equipment does not cater for ‘home based’ food production that can be carried out by the residents, in their own kitchens.

Processes and Equipment (ref. 13):

Drying will be necessary to process green matured grains (wheat) and legumes (soybeans) before threshing or depodding.  A Drum Dryer/Separator can carry out all these processes as well as mixing, sieving and seperating and the cleaning, washing, peeling and draining of vegetables.  This instrument consists of a drum placed in a case with a heater, fan, air inlet and outlet.  The air, which is heated and circulated in the case, heats the drum, which rotates at 10-200 rpm.

In order to make flour from the grains and soybeans, to produce sugar from beet and to make powders such as agar a mill will be necessary.  This consists of a ‘centrifuge’ mill with replaceable screens to enable varying degrees of coarseness.  These will be necessary to produce suitable flours for such differing purposes as pasta production and bread manufacture and to enable other equipment to perform efficiently.

A further way to grind the grains and beans is provided by a food processor.  This can carry out course milling; the mixing of powders; the dispersion of liquids or solids in a liquid; the preparation of juice; the kneading of dough; and the slicing, shredding, chopping and pureeing of foodstuffs.  This equipment has a low power consumption (~0.33kW/person) so provides a lightweight, low waste producing step in the production of many foods.

For the purposes of heating foods during refinement, a Microwave/Convection Oven (MCO) can be used.  This can be used to heat, boil, cook, broil, bake, roast, defrost, dry, and melt but also, more importantly in this stage of manufacturing, pasteurise, gelatinise starch, inactivate enzymes and denature proteins.  These processes produce little waste (any created tend to be aromatic vapours) on an energy budget as low as 0.83kW/person.  The forced air system of this equipment allows for faster cooking and operations in various levels of gravity.  An alternative to the Microwave/Convection Oven is the High Air Velocity Oven (HAVO).  Both can be used in conjunction, however the HAVO adds more palatability and texture to foods.  Unfortunately the HAVO requires a 1500W heater to provide temperatures between 65 and 205oC.  This along with the air speed halves conventional cooking times, although they are still equal to those of the MCO.  For these reasons the MCO will be used for all major food heating/cooking requirements, however the HAVO, with a tightly sealed lid, must be used for the production of Tempeh (a fermented soy bean cake similar in texture to tofu).

For the purposes of extrusion a heated mixer will be provided.  This will be capable of cooking, boiling, and mixing but its main additions to the equipment will be fermentation and the heated blending of powders, later to be processed in the extruder.  Extrusion, using a high temperature (140-170oC) while in vapour release mode, is capable of producing cereals, grain (specifically rice and wheat) flakes, soup additives (from seaweed, soybeans and other legumes), crispy bread, gelatinized starch, precooked rice and bulghur (wheat kernels that have been steamed, dried and crushed).  Also, at high temperatures, using the suppressed vapour release mode, the extruder can produce textured proteins (an important meat or fish analogue extruded from soybeans), rice noodles and crisps (potato chips).  Further foodstuffs can be produced using low temperature extrusion, which helps form pasta products and expels oil (very important on DL4 for vegan diets). 

Extrusion may only require about 0.2 kW/kg of product and with little waste (much of which can be processed on the second run) the unit is highly efficient with a large range of uses.  DL4’s extruder would be used in conjunction with the mixer and the Drum Dryer/Separator, in order to dry (if necessary) and to furnish the finished product with colours, spices and flavour.  Products from the extruder, which were made at high temperatures, offer the additional advantage of long shelf lives due to low water activity levels.

In order to process grains and beans into flakes, it will be necessary to use a flaking roll. Flaking provides a further processing step for extruded products, allowing some of them to be eaten as snacks.  Bread, from the various types of grains, will be easier to produce if the process is automated using a bread baking machine.  This would reduce the load on the Microwave/Convection and High Air Velocity Ovens and cut back on energy requirements.

During the process of soy milk and margarine production, it will be necessary to homogenise (evenly distribute and break down fat globules) the products.  This will also be a necessary step in the separating of cereal (wheat) starch and gluten.  This process would be complimented by a centrifuge, which will be capable of such starch/gluten separation as well as the precipitation of soy bean proteins in tofu processing and the removal of excess water from vegetables.  The starch separated in this process may then be used as an ingredient for extrusion products, and in the process of sugar refinement and other fermentation processes.

For the purposes of a constant food supply onboard DL4 it will obviously be necessary to provide equipment, on a large scale, for the refrigeration, freezing and storage of foodstuffs.  Many of the processes used, for major food production, lead to products that have a long shelf life and require little further treatment for storage.  However, for those products that do require freezing (e.g. - tofu), the use of suitable equipment in lower than 1g areas would be slightly more efficient.  This is due to the reduced convection with a lower amount of forced air.  Freezing/Refrigeration will also be useful for food processing activities, such as: texturisation, gelation, chilling drinks and foods and ice formation.