• BREAD MAKING

• Bread is one of the most consumed food products known to humans, and for some people, it is the principal source of nutrition. different from most other food fermentations:
• -the purpose is not to extend the shelf-life of the raw materials (starting material is much more perishable than the finished product)
• -none of the primary fermentation end products actually remain in the food product
• contains carbohydrates, lipids, and proteins, essential vitamins of the B complex and of vitamin E, minerals and trace elements.
• There are numerous variations of the breadmaking process; tradition, cost, the kind of energy available, the kind of flour, the kind of bread required, and the time between baking and consumption of bread.

Principal ingredients

• Flour
• The most important characteristics of flour:
• the quantity and quality of gluten,
• the water absorption capacity,
• the diastatic activity.
• After kneading: cohesive, viscoelastic mass retains the gas formed
• YEAST

• Commercial yeast production in the world: exceeds 1.8 million tons/year.
• used by: the baking, brewing and distilling industry
• Yeast is also a commercial source of natural flavourings, flavour potentiators and the dietary supplements.
• first compressed yeasts: in England at 1792
• The large-scale commercial production of bread: in the US at 1868, by Charles Fleischmann.
• yeast strains are developed
• – to tolerate high sugar
• – to tolerate high salt concentrations
• – to high temperatures used in fermentation
• Currently: more than 500 species of yeasts, belonging to around 50 genera Saccharomyces: ‘sugar fungus’
• S. cerevisiae have been isolated from : breweries, wine, berries, cheese, pear juice, honey, eucalyptus leaves, kefir.
• Reproduction
• Asexual reproduction usually occurs by budding.
• Sexual reproduction

Bakers’ yeast ( S. cerevisiae.)

• Based on moisture content: compressed (most common), granular, dried in the form of a pellet, instantaneous, encapsulated, frozen, or in the form of a ‘cream.’
• Based on maltose adaptation: standard and rapid
• Tolerance to high osmotic pressure : important in frozen dough.

Hybrid Strains

• rapidly fermenting strains: produce high volumes of CO2 for automated bakeries
• strains with intermediate activity, for traditional bakeries;
• and strains which ferment more slowly, for in-store bakeries.

Growth Requirements

• S. cerevisiae is a heterotroph, i.e. requires organic compounds for growth. a mesophile, growing best in the temperature range 25–40°C. Glucose and fructose are readily utilized,
• sucrose and maltose are preferred.
• Other malto oligosaccharides can also be utilized,
• S. cerevisiae cannot utilize pentoses, other hexoses, the disaccharides lactose or cellobiose or the polysaccharides.
• In industry, the preferred carbon sources are cane or sugar-beet molasses( fermentable sugar conc. of 50–55% and around 80% total soluble solids. )

Nitrogen

• can utilize – inorganic nitrogen (ammonium sulphate, ammonium chloride, ammonia. -Urea

Minerals The major minerals required: phosphorus, potassium, calcium, sodium, magnesium,s ulphur.
Vitamins S. cerevisiae requires : biotin, pantothenic acid, inositol and thiamin
These (except for thiamin)are available from molasses. Sugar-beet molasses, however, is deficient in biotin
Oxygen
• S. cerevisiae possesses a remarkable ability to adapt to varying levels of available O2.
• very low levels of O2: : shuts off the respiratory enzymes. ( ‘waste’ product is ethanol.)
• When adequate O2 is available; sugar is converted by the respiratory enzymes to CO2 and H2O
• The max. theoretical yields of yeast solids:
•microaerophilic (anaerobic) :7.5 kg/100 kg of sugar utilized.
aerobic conditions : 54.0 kg/100 kg of sugar utilized
If > 5% glucose: TCA (tricarboxylic acid) cycle is almost completely blocked.
Even if the culture is aerated, glucose can only be fermented, this phenomenon being known as the ‘glucose effect’ or the ‘Crabtree effect’.
• For aerobic growth: sugar has to be supplied incrementally μ does not exceed 0.2
•and the respiratory quotient (RQ) is maintained at 1.
•S. cerevisiae grows optimally at pH 4.5–5.0, can tolerate a pH range of 3.6–6.0.
Temperature
•S. cerevisiae has one of the shortest generation times amongst yeasts, 2.0–2.2 h at 30°C.
•Bakers’ yeast production is optimal: at 28–30°C.
Preparation of Medium
•The molasses (containing 50% fermentable sugars and 80% soluble solids) is usually diluted with an equal weight of water, and the pH is adjusted to 4.5–5.0 with sulphuric acid.
•Then clarified using a centrifuge or filter.
•The clarified molasses is then sterilized by the high temperature short time (HTST) process.
defoamer (silicone, edible oil), 0.01 g l−1.
•The molasses is then transferred to the fermenter, pitching yeast.
•More clarified molasses: the fed-batch cultivation.
Cultivation
•In industry, stainless steel fermentors with a capacity of 200 m3 or more are used.
•bubbling compressed air
•eight stages, from 0.2 kg of yeast to 100 000 kg of yeast. (the entire process is known to involve 24 generations of the yeast)
• a typical cultivation tank : airlift fermenter.
•Metabolic heat generation: 14 650 J/ g yeast solids, to keep temp at 28–30°C, cooling is necessary.
If the depth of the broth> 3 m,
use of compressed air
Maturation : At the end of the final stage of yeast cultivation, the feed rate is greatly reduced results in a low proportion of budding cells, which confers higher stability on compressed yeast in storage.
Finishing Stages
•Yeast Cream (20% yeast solids)
continuous centrifuge at 4000–5000 g.
•Yeast cream can be stored at 4°C for few days
•Compressed Yeast
•from yeast cream by Rotary vacuum filters .
•mixed with 0.1–0.2% of emulsifiers( monoglycerides, diglycerides, sorbitan esters and lecithin,)
•then extruded through nozzles.
•cut and packaged ( 500 g) in wax paper or polythene sheet.
• must be rapidly cooled, and stored at 5–8°C.
•Active Dry Yeast (moisture content of 4.0–8.5%. )
•Active dry yeast is stored at room temp.
•produce thin strands or small particles, then dried in a tunnel drier, ( 2–4 h the air inlet temp. 28–42°C. )
•continuous drying, fluidized-bed drying, airlift drying
•Emulsifiers ( sucrose esters or sorbitan esters, 0.5–2.0%) are mixed to facilitate rehydration.
•Antioxidants ( butyl hydroxyanisole(BHA) at 0.1%), added to prevent undesirable oxidative changes.
•1 g compressed yeast ≡ 0.4-0.45 g dry yeast
•Rehydration:
•X g yeast + 4X g water at 37.8-44.5 C
•T < 32 C …..or T>46 C
–The glutothione leaches out of yeast and causes to dough become soft and sticky
–Cell contents ( a acids, vitamins, nucleic acids,
coenzymes,glutothione and inorganic salts) leaches out and fermentative power of yeast decreases.
• heat resistant strains are used: heat resistant strains generally carries low gassing power.
Temperature
• at 4 °C, no activity, no fermentation
• at 10–15 °C, yeast activity, fermentation; slow
• at 20–40 °C, fermentation ; very active
• at 45 °C yeast activity slows down
• at 55 °C, the yeast dies.
•pH
•very tolerant to fluctuations in pH (2–8),
•but the optimum pH :4 and 6.
•the pH of dough is 5
Presence of Dough Inhibitors
The Cu and Cl in water, inhibits fermentation
•acetic and propionic acid, fermentation inhibitors
Sources of Sugar used by Yeast
•Yeast uses
•(1) trehalose (Trehalose is a non-reducing sugar, two glucose ( 1-1 alpha bond) very resistant to acid hydrolysis)
•(2) free sugar from flour
•(3) sugars obtained by the action of enzymes
•(4) added sugars such as sucrose.
•Order: 1- trehalose 2-free sugars and sugars added 3- maltose.
Production and Retention of Gas
•Kneading ; air is incorporated into the dough.
•These bubbles contain mainly nitrogen; low solubility in water
•Yeast cannot create new bubbles
•The more bubbles: finer the grain.
•CO2 is produced in the aqueous phase, as pH decreases this phase becomes saturated with CO2 .
•the newly formed CO2 is retained in preexisting bubbles.
•the quality of gluten is important to retain the gas
•At the pH of dough, most of the carbon dioxide is present as CO2 and a small amount of this as CO32− HCO3−, or H2CO3.
•Half of the total CO2 produced is lost in initial fermentation, punching, rounding, molding, and final fermentation.
Salt -to provide flavor, influence the rheological properties of dough.
• Higher concentrations of salt inhibit enzymatic reactions and also inhibit the fermentation.
•salt used: 1–2% (based on flour weight).
Optional Ingredients
•Fat
•increases the shelf-life,
•produces a finer grain,
• yields a greater volume of baked foods
•The crust is more elastic and softer.
•The shortening effect ( film between the starch and protein)
•The shortening effect is greater for fat with a lower melting point than for harder fats. ( hydrogenated vegetable fats)
•the use of fat requires less water in the formulation
Sugar
•promotes fermentation, browning of the crust,
•sweeter taste, dough more stable, more elastic, and shorter, and the baked goods more tender.
Milk and Dairy Products ( skim-milk powder, whey)
•promotes browning, a softer crust, a longer shelf-life
Oxidants ( the oxidation of -SH groups of protein )
•improved gas retention, firmer gluten, dough maturation is shorter, the oven spring is greater, the volume is larger,
The oxidant commonly used is ascorbic acid
Enzyme Active Preparations
•Flours with a low enzyme activity: yields
breads that do not brown well, stale rapidly.
-Add fermentable sugars or enzyme active preparations((malted flour, malt extract, and bacterial or fungal α-amylases).
•Emulsifying Agents(monoglycerides, lecithin)
to make bread softer during storage,
•staling is delayed.
steps in breadmaking
• Ingredients:flour, water, salt, yeast
Mixing:
Rules for mixers
•-use 90 % of maximum capacity designated
•-if producing sponge use 60% of max capacity
•-don’t go below half of the maximum capacity designated
•hydration of protein to form gluten and the spreading of the gluten over the surface of the free starch granules to form a continuous matrix.
• otherwise a clay-like dough will result that will lack gas retention.(if Protein < 7% )
if excessive amounts of the starch granules are damaged in milling ; sticky dough results
•Mixing time(↑) = f of
• T(↑),
• absorption level(↑),
•flour strength(↑),
•salt addition,use of oxidizing agent, reducing agent(↓),
•enzyme supplementation (↓),
•mixer design ( mixing bar area↓ )and speed
•Stages of mixing
•1 – uniform blending
•2- pick up stage , gluten begins to form
•3- clean up stage , most important reference point, drier and more elastic dough, this stage is completed when the dough clears away from the mixer bowl
•4-development stage , critical
•5-overmixing ( let down stage)
Heat production during mixing:
•Due to dehydration 6.5 btu / lb flour
•Frictional heat 42.5 btu/hp/min
•keep temp of the dough: ( 25.5-27 C) by
•adding ice
•use chilled water
•refrigeration
Dough divider :
•Divide dough volumetrically 9600 dough pieces /h
•lubricated with mineral oil to prevent sticking of dough while dividing
Rounding:
• Dough with a rotary motion produces a ball-shaped piece with smooth skin.
improves the retention of gas.
•Dough is less viscous.
•After rounding, dough needs a floortime (2 to 20 min) Conical rounder
•Moulder The function of moulders is to sheet, curl and seal the rounded dough pieces
• O curling pressure
•Dough ball → thin sheet → cylindrical shape → sealing
• O of dough rolls board
•Rollers ( 2 to 3 in series)
•To prevent moisture accumulation on one end of the sheet after two rolling direction of rolling reversed
•The molded dough is placed either in tins or on a baking tray and kept in a proofing cabinet continue fermentation (final proof).
Fermentation, Final Proof, or Proving:
-starch is converted into sugars by enzyme action.
-sugars CO2 and ethanol
-as CO2 produced, the dough expands and retains it, the skin should remains flexible.
-retained gas =f (quality of the gluten )
– The more retained gas, the more bread volume.
The temperature =f(the kind of bread and the breadmaking process (28–30 °C)
– The RH :60 and 90%, =f( formulations and ferm. temp.)
•If the relative humidity is < 75%, the skin of the dough will be very dry and will lose its elasticity. •Initially, dough has a pH of about 6.2, and during fermentation, the values are about 5.76 or 5.67. •acidic environment improves the formation of gluten •The capacity of dough to withstand excessive mechanical work is called dough tolerance.( doughs that ferment slowly are more tolerant.) •Tray type proofer •Straight Dough Method •• Advantage: •less processing time, labor, power, and equipment. •Fermentation losses are smaller •• Disadvantage: •small variations in processing lead to noticeable variations in the final quality of breads. •less flexible than the sponge dough, •requires limited fermentation time, does not permit correction of overfermentation. •do not have a soft texture, •the bread volume is lower, •Sponge and Dough Process permits the use of strong and soft (weak) flour, using the strong flour to make the sponge and the soft in the final dough. (50% / 50%.) • Advantage: • permits greater variations in the operations of the process improves the volume, texture, and shelf-life of the bread. •the longer fermentation time….more aroma. •Disadvantage: •more fermentation time and labor than the straight dough method, • more difficult to control. •difficult to divide, laminate, and mold. •How to manipulate fermentation time? •By amount of yeast: y*t/n=x •y: percent yeast used normally •t: normal fermentation time •n: new fermentation time •x: percent yeast for new fermentation time •2% yeast 4 h fermentation •To reduce 3 h we need 2*4/3=2.66 % yeast needed ( one can vary fermentation time by 30% in both direction but not more than that) •If greater changes required, changes in other parameters should be considered such as fermentation temperature and fermentation substrate. •0.5 C ferment time by 15 minutes •At most 45 minutes of change is allowed by temp. change •BAKING •Temperature of Baking •the baking temp. 200–275 °C is a function of the type of baking oven, the duration of baking, and the size and type of bread desired (formulation used). •small items :a higher temperature and a shorter time •large items :a lower temperature and a longer time. •soft dough (low consistency): a higher temperature than hard dough •hard dough (less water to evaporate) Duration of Baking •duration of baking depends on the temperature used. •During baking, the following changes take place: gelatinization of the starch, •denaturation of the protein, •the formation of aromatic substances. Relative Humidity •injection of satd steam into the oven RH •dough is covered with a fine surface layer of water, which keeps it moist and elastic for some time. •advantages: delayed formation of crust, increases the volume (with a satisfactory oven spring), improves the color and shine, and produces a fine crust. • low pressure steam, 2-5 psia saturated, is added during first minute of baking) •if steam is not added → • surface dries out quickly because of inadequacy of moisture, •surface layer starch undergoes pyrolysis rather than partial gelatinization •crust will not acquire the desired gloss •the evaporative process absorbs considerable heat from the surface thereby slowing the rate of heat penetration into the loaf interior. •Type of Oven •Heat tr. by conduction, convection, and radiation. •Coal, oil, or electricity may be used to heat the oven the most common: •the hot air oven, rotary hearth oven, the reel oven, the pan rack oven, a continuous belt, tunnel oven •Transfer of heat •Convection, radiation and conduction on the surface (> 100 °C)
the crumb inside (< 100 °C)
•Energy requirement
•Approximately 235 btu ( 150-250 ) is needed to bake 1 lb of bread ( = f ( oven temp and initial dough temp)
•Cp of dough 0.65-0.88 btu/ lb-C
•Modern oven heat input 325-400 btu / lb bread
•Coal-fired brick peel ovens 1780 btu / lb bread
•Relative heat utilization :
•Heating medium calorific value heat needed to bake fuel needed per 100 lb
• ( btu / lb of bread baked) bread baking
•1- natural gas 1000 btu / ft3 800 80 ft3
•2- manufactured gas 546 btu / ft3 610 112 ft3
•3- fuel oil 140000 btu/gal 950 0.76 gallons
•4- electricity 3412 btu / kwh 475 13.9 kwh
•*natural gas is cheapest and electricity is most expensive one
•*sp.gr. of propone = 1.5 times sp gr of air, sp gr of natural gas = 0.5 times sp gr of air
•*baking time and temp =f( product formulation)
•lean formulas call for higher temp and shorter baking time than richer ( containing sugar and dairy ingredients enter readily into thermal browning reactions formulas)
•Cooling
•reduce temp quickly to 35-40 C, final bread moisture •in slicer not to obtain crippled
•undesirable moisture condensation in the package
Wash cooling chamber with
detergent and use microbiological
filter for air to prevent
mold infection. →→
•Physical–Chemical Changes During Baking
•There are three phases depending on the temperature the dough reaches:
•1. oven spring (enzyme active zone) (from 30 to 60 or 70 °C); ( due to 57 % gas expansion, 39 % decrease in gas solubility and 4 % increased yeast activity)
•2. gelatinization of starch (55–60 °C) to no higher than 90 °C;
•3. browning and aroma formation above 100 °C
•Pan Breads
•breads that are baked in pans, either open or closed.
•in North America, Eastern and Western Europe, Australasia,
•automated or semi-automated equipment.
•always sold presliced in polyethylene bread bags
•Hearth Breads (artisan breads, rustic breads), french, italian bread
•stiff and dry doughs; baked directly on the hearth, or floor, of the oven, without pan
•Buns and Rolls ( for Hamburger and hot dog )
•richer in formulation
•while rolls tend to be made from leaner formulas
•(baked with steam, light, slightly crispy crust)
•Flat Breads
•These are the most widely consumed of all bread types.
•Single-layered flat breads
•North and Central Americans: tortilla.
•Tanoor bread : Middle East, India, and Pakistan.
•( wheat flour, soda (sodium bicarbonate), yeast, and water) Sourdough can be used in place of the yeast.
•Ciabatta : lean formula sponge dough, usually consisting of wheat flour, water, yeast, and salt.
•double-layered flat bread : Arabic bread (pita bread)
•pocket is formed largely by a second proofing step that is not given to single-layered flat breads.
•Baking :at high temperatures, normally 400 °C, for short periods of time, 90–100 s. (enhance pocket formation)
•KEEPING OF BREAD
•Crust staling :
•crust 12 % m, crumb 44-45 % m
•storage in a closed chamber…. crust moisture increase to 28 % ( this moisture is taken from crumb, also from air air if conditions are suitable )
•( this is staling ) crust staling is irreversible
•crumb staling :
• moisture loss of crumb, starch retrogradation, modification of protein structure
•surface active agents -keeping crumb softness longer -improvement in mixing and fermentation tolerance -better moisture retention –opt loaf volume
Retardation of staling
•-surfactant
•-bread from high protein flour stale less than low protein flour ( higher specific volume of bread slower firming rate)
•-adding milk products
•-small amount of glycerol ( 0.5 %)
•- use of lecithin
•- adding malt extract ( due to amylolitic activity )
•- soy flour and soy isolate addition
•-shortenings
•-short time dough process staling < long time dough process staling
•-low temp freezing is the most effective way of retarding staling
•store at -9 C for 3 days and then thaw → like fresh bread
•store at -34.4 for 30 days and than taw → like fresh bread
•to stabilize bread its temp has to be lowered below its freezing point which is about -6.7 C
•at -23,-29 C with air speed of 200-500 ft / min reaches freezing point in 2 hrs then keep at -18 C
•one can prevent staling by keeping bread below -18 C and above 55C but keeping above 55 C will accelerate rope formation.
•Ropiness:
•bacterial spoilage of bread: initially unpleasant fruity odor, followed by enzymatic degradation of the crumb that becomes soft and sticky because of the production of extracellular slimy polysaccharides
•primarily Bacillus subtilis
•and occasionally Bacillus
• licheniformis, Bacillus pumilus,
• and Bacillus cereus
Trabzon Vakfıkebir Bread ( around 3000 g. )
•late staling due to high internal moisture ( approx 48 %) and lower cooling loss ( 9%, normally 15-20 %).
Baked at 170-180 C for 115 min ( total processing time ≈20 hours)
•Properties: -indirect dough method , -thick and tough crust -long processing time and high tolerance → yields highly aromatic bread
•-long shelf life -late staling- one week:due to sour dough→ delays enzymatic breakdown of starch so water holding capacity is high as a result unfermented sugars are responsible for delayed staling. if 36.8 % •production flow sheet:
•10 kg sour dough from previous production ( first sour dough)
• ↓ 15-18 hours of rest
•second sour dough preparation ( 20 min ) …first sour dough +25 kg flour + water 20 min
• ↓ kneading → tough dough (25 C, 75 % RH, rest 3 h)
• main dough mixing ( 25 C , 22 min) 100 kg flour+ second sour dough 20 kg
• ↓ 22 min kneading +30 min resting+20 sec kneading
•main fermentation (25 C , 135 min, 75% m)
• ↓
• dividing dough by hand ( 3400 g)
• ↓
• rounding by hand ( by hand)
• ↓
• final fermentation ( 25 C, 100 min, in cloth covered plastic pans )
• ↓
• shaping ( add some flour to original dough to proper tougher dough,
• prepare cylinder of 1 cm diameter and 20 cm length for lining)
• ↓
• baking ( 170-180 C , 115 min)
Sourdough Fermentation
•Most yeast breads have a slightly acidic pH, due to acids produced by the yeast and, dissolved CO2 in the dough. acids also are produced by lactic acid bacteria (present in the flour, in the yeast preparations, or in )the dough.
•The perception of sourness occur when the pH is near 4.0( yeast breads pH 5.0 to 6.0 )
•If lactic acid bacteria added : the pH <4.0, sour but appealing flavor , better preservation.
•the very first breads made: sourdough breads.
Commercially available.:in addition to L. sanfranciscensis, available strains include L. brevis, L. delbrueckii, and L. plantarum.
•authentic sourdough breads are almost always made via a sponge and dough process.
•RYE BREAD
rye : second most common cereal ( to make bread.)
rye : high conc. of pentosans ( xylose, arabinose, 4 to 5 times more than that found in wheat.)
•may have both positive and negative effects.
•1-high water-binding capacity, decrease retrogradation and delay staling
•2-interfere with gluten formation, giving an inelastic dough that retains gas poorly.
•rye proteins do not form a viscoelastic dough.
( a small loaf volume and a dense crumb texture. )
• rye flour contains more α amylase (excessive starch hydrolysis, poor texture and reduced loaf volume.)
•The addition of sourdough cultures compensate for these complications.
• -1-as the pH decreases the pentosans become more soluble, begin to swell and form a gluten-like network that enhances dough elasticity and gas retention( act like gluten.)
•2-at low PH α amylase lose activity so excessive hydrolysis is avoided.
•3-Some sourdough bacteria also have the ability to ferment pentosans
• 4-acidic conditions enhance the water-binding capacity of the starch granules, decreases staling
•Another potential problem of rye bread and other whole grain breads:
•the presence of phytic acid that is capable of binding zinc, iron, calcium, and other divalent metal cations, preventing their absorption in turn reducing the bioavailability of essential minerals
•Cereal grains:as much as 4% phytic acid
•whole grain bread: less than 0.2%, this is still enough to be a nutritional concern.
•Solution to phytic acid problem: Degradation of phytic acid via the enzyme phytase, which is present in flour and is also produced by yeasts.
•Lactobacillus sanfranciscensis, Lactobacillus plantarum, and other sourdough bacteria also produce this enzyme
•Thus, the sourdough fermentation also enhances the nutritional quality of rye and other whole grain breads.
•FROZEN DOUGH
•One of the hottest trends in the baking industry
•small retail bakery operations: eliminate the need for dough production equipment and labor,
•The frozen dough, produced somewhere else and brought to small bakeriesw where they are thawed overnight in the refrigerator, given a final proof, and baked.
•the quality of bread varies: due to the loss of yeast viability during storage.
•Doughs made using cold-sensitive yeasts require longer proof times
•the normal bakers’ yeast: cryosensitive that they may fail to provide any leavening at all after the dough-thawing step.
•for frozen dough: yeast strain must be cryotolerant.
•What makes some yeast strains resistant to the effects of freezing? And what can be done to improve cryotolerance
•cryotolerance in S. cerevisiae is due the ability of the organism either to transport extracellular cryoprotectant solutes from the environment or to synthesize them within the cytoplasm.
•these agents prevent dehydration, by re-structuring the bound water in the cytoplasm.
•Microbial cryoprotectants are typically small, polar molecules: amines (e.g., betaine, carnitine, proline, and arginine), and sugars.
•In S.cerevisiae, the disaccharide trehalose is the most important cryoprotectant (although some amino acids like arginine also have cryoprotective activity).
when environmental stresses ( like low temp) are applied the cell responds by increasing synthesis of trehalose. ( and transporting extracellular trehalose, if available).
•under non-stress conditions, the enzymes used to synthesize trehalose are turned off and the hydrolytic enzymes turned on .
•Trehalose can also serve as a storage carbohydrate .
• If, the trehalose degradation pathway is blocked, then higher levels of trehalose can be maintained, making the yeast more cryotolerant.
•Arginine hydrolyzing enzyme arginase was inactivated. This led to increased intracellular concentrations of arginine and an increase in freeze tolerance and gassing power compared to the parent strain.

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