Midterm Questions

FE471 2007 1st

1) What are the cold break and hot break?

– Protein precipitation; to have colloidal stability of the beer, high molecular proteins forms large flocks and precipitate this is called as “hot break” or “trub”.

– Wort is cooled to 48 C in a heat exchanger; there will be some additional protein precipitation, which is called as “cold break”.

2) Back-slopping and DVS culture advantages and disadvantages?

– Directly into the food material, thus eliminating the need to grow bulk cultures.

–  ‘direct-to-vat set’ or DVS.

– Of course, such cultures are also widely used in the sausage, baking, and other industries, where product volumes are usually small,


  • Eliminating the labor, hardware, and accessory problems.

  • DVS cultures must be highly concentrated, especially those used for cheese manufacture.

  • The added concentration steps may reduce culture viability, causing slow-starting fermentations.

  • Direct-to-vat cultures are also more expensive to purchase than bulk cultures, and may not be economical for large-scale operations

3) Main principle of airlift fermentor?

In the internal-loop design, the aerated riser and the un-aerated down comer are contained in the same shell. In the external-loop configuration, the riser and the down comer are separate tubes that are linked near the top and the bottom. Liquid circulates between the riser (upward flow) and the down comer (downward flow).

Generally, these are very capable fermentor, except for handling the most viscous broths. Their ability to suspend solids and transfer O2 and heat is good. The hydrodynamic shear is low. The external-loop design is relatively little-used in industry.

4) What is the fed-batch fermentor and principle of it?

                An enhancement of the closed batch process is the fed batch fermentation. In the fed-batch method the critical elements of the nutrient solution are added in small concentrations at the beginning of the fermen­tation and these substances continue to be added in small doses during the production phase

5) How we prevent the contamination of product during fermentation? And what is one in thousand principles?                

6) High temperatures kilning?

– a stronger malty flavor

– a deeper color,

– reduce enzyme levels,

– More unfermentable dextrins greater body in the final beer 

7) What and why blending is made?

        Many consumers want the same taste, color and fragrance in each bottle under a particular label. However, such uniformity is difficult to guarantee in a product so volatile as wine, because sunshine and moisture vary from year to year and so the grapes from each vineyard vary annually.

There are different times to blend:

a) Blending different grapes while they are being crushed.

b) Young wines are blended soon after fermentation.

c) Many wines of varying ages are blended after they are mature.

8) What are the Sake unique properties?

                Uniqueness of sake:

• mold enzyme is used to achieve saccharification

• natural fermentation ( not very aseptic conditions )

• simultaneous saccharification and fermentation

• solid state fermentation (high level of solid content)

• low temperature fermentation

9) How do you produce low or non alcoholic beer? Write 3 processes

– By removing the alcohol from a full-strength brew

– By vacuum distillation or reverse osmosis,

– By restricting the ability of yeast to ferment wort,

– By making a wort containing very low levels of fermentable sugars( limiting activity of beta amylase)

– By ensuring that the contact between yeast

– Wort is at a very low temperature  

10) Undesired acid in wine? What are the steps of tartaric acid chilling process in wine?

Tartaric and L-malic are undesired acid in wine fermentation. For tartarate removal wine is chilled to 0-2 C (4-10 days) to crystallize tartaric acid. And to precipitate it then it is racked to remove tartaric acid crystals 

11) What are the generalizations of GAP, ED, PP pathway?

 The three pathways differ in many ways, but two generalizations can be made:

– All three pathways convert glucose to glyceraldehyde 3-phosphate (GAP) by different routes.

– The GAP is converted to pyruvate via reactions that are the same in all three pathways

12) Why do we use Pectic enzymes in wine?

                Pectic enzymes are also used as clarifying agent. Catalyze the chemical breakdown of the pectin’s in wine. This pectin’s act as protective colloids holding other constituents in suspension in the wine, giving the wine a cloudy appearance when the enzyme “break down” these pectin’s a clarifying action is achieved 

13) Phage (Bacteriophage) steps?

– The most frequent cause of poor starter performance, apart from process failures such as low-temperature incubation, is infection by bacteriophages (phage).

– These are viruses that attack bacteria and have caused problems in the cheese industry for decades.

– Infection of the bulk starter tank may not be immediately apparent, the pH being unaffected.

– This situation arises when the bulk starter vessel is not grossly infected, and the inoculum passes through a number of growth cycles before it is killed completely.

– If the infection is in the cheese room, there is a slowing of acid development, culminating in a ‘pack-up’, a ‘dead’ vat, in which there is no acid development between starter inoculation and salting.

– At best, such cheese can be processed; at worst, it can only be used as feed.

14) What is denatured Alcohol?

Gıda dısında kullanılan alkollere denature alkol denilmektedir.

FE471 2007 SECOND

Q1. What is the Balsamic Vinegar?

Balsamic vinegar

– The juice of white grapes boiled down to 50% of its original volume to create a concentrated must,

– Which is then fermented with a slow aging process which concentrates the flavors?

– The flavor intensifies over decades, with the vinegar being kept in fine wooden casks, becoming sweet, viscous and very concentrated.

– The liquid is transferred to successively smaller casks made of different woods, absorbing the flavor characteristics of each wood and becoming more concentrated with each transfer.

– A small (100 ml) bottle can cost between US $100 and $400.

– Less expensive varieties may not be aged in wood at all, being nothing more than ordinary wine vinegar with coloring and added sugar.

Color: Dark brown

Density: Fluid and syrup like consistency

Fragrance: Distinct, complex, sharp and unmistakably but pleasantly acid

Flavor: Traditional and inimitable sweet and sour in perfect proportion.

Use few drops; very expensive

Q2.What is the reasons of L (+) lactic acid greater than 70?

• Starter culture was predominantly S. thermophilus

• fermentation temperature <40 C

• product is cooled at low acidity and cooled product has <0.8% Lactic acid

Q3. What is the maceration and methods of its? Explain

• Maceration ruptures the leaf cell structure, exposing the chemical constituents of the cells, mainly polyphenols, oxidative and degradative enzymes, lipids, amino acids, etc., to oxygen.

• Most importantly, catechins come into contact with the polyphenol oxidase enzyme, initiating ‘tea oxidation,’ which is erroneously referred to as ‘fermentation.’

The most common methods:

The orthodox rolling, crush, tear, and curl (CTC), and Laurie tea processor (LTP) methods.

• The method used has a significant effect on the resultant black tea.

– Orthodox rollers: less cell matrix destruction, leads to fewer oxidative reactions,  slow fermentation (Tea is plucked by hand, the top two leaves and the bud is plucked in a fine plucking. select the newest growth of the tea plant )

– CTC (Tea is harvested by machine. CTC methods cut off a foot or more of the tea plant. The stems are processed along with the leaf by the CTC method. )

– LTP maceration methods: greater cell matrix destruction, more extensive oxidation, less aromatic tea, higher plain tea quality parameters (more intensive color than orthodox)

• LTP requires a softer physical wither than CTC processing.

• The action also aerates the mass of tissues and causes some temp increase. 

Q4. Explain Phase II?

Phase II

• Compost in wooden trays …

• live steam injected temp reaches 60 C for  2-4 hours

• during next 6 days temp drops to 30 C ( thermophilic growth)


• eliminate free ammonia ( which is toxic to mushroom, and produced in phase  I ) by either being converted to protein by thermophilic m.o.s or evaporated

• pasteurize the compost to eliminate m.o.s, insects and pests

Q5. How increase the mushroom shelf life?

• Gamma Irradiation at 100 Krads improves shelf-life

• Trimming the stipe of cultivated mushrooms (Agaricus bisporus) from 35mm to 5mm from the cap immediately after harvest resulted in improved shelf life as indicated by reduced browning and slower cap opening  

 Q6. What is the Bloaeter damage? How eliminate its effect?

Bloater damage occurs due to high level of gas production during fermentation.


  • large cucumbers (with thick skin)

  • Higher fermentation temperatures (which supports growth of gas producing bacteria such as coliform, hetero-fermentative lactic bacteria and yeast).


Inoculating with L. Plantarum  purging out produced CO2 with nitrogen gas definately using small size cucumbers will

Q7. Explain phosphates and GdL using?

• Phosphates and polyphosphates are used primarily to increase the water-holding capacity of cured meat products.

• Alkaline phosphates increase the pH of the meat and also help in solubilizing muscle proteins in order to impart the water-retention action.

• In addition to increased water binding (i.e., increase in product yield), phosphates improve the cured meat flavour by retention of natural juices and by reduction of oxidative rancidity.

• They also help improve retention of the cured meat colour.

• Phosphates: sodium pyrophosphate, monosodium phosphate, sodium hexametaphosphate, disodium phosphate, sodium tripolyphosphate and sodium pyrophosphate, as well as mono- and dipotassium phosphate, potassium tripolyphosphate and potassium pyrophosphate.

• Tripolyphosphates and their combinations with hexametaphosphates are the most widely used phosphates for cured meat cuts, as they provide the proper pH, good solubility, calcium compatibility and a high degree of the protein modifying effect.

– Glucono-δ-lactone (GdL, 0.5%) to ascertain fast chemical acidulation with negative effects on flavor development;

– (GdL) is only used for products with a short shelf-life (Because many strains of lactic acid bacteria ferment this compound to lactic and acetic acid interferes with reactions leading to and stabilizing desired sensory properties.)

Q8. How can you eliminate Bitterness of olive? Which compound responsible with bitterness?

– Oleuropein is the compound responsible for the bitterness of the fruit

– Bitterness of fruit can be eliminated completely and quickly by alkaline hydrolysis, that is, by treatment of olives with sodium hydroxide solutions prior to fermentation and by storage in brine or dry salt. These fruits are generally called pickled olives.

– Bitterness may also be eliminated slowly and partially without prior to alkaline treatment during the acid fermentation by placing the fruit directly into brine or by preserving it with dry salt.
These types are generally known as olives in brine or olives in dry salt.

Q9. Write 5 defects about olive, explain 2 of them.

Ø  Film formation on the surface of tanks( soft pickles):

Ø  Slime formation

Ø  Darkening:

ü  Occurs in green olive pickles due to contact with air. Also iron contamination cause darkening by reacting with polyphenols and forming iron tannat.

ü  If darkening is not intense, keeping olives in 1-2 % H2SO4 solution can be helpful to remove dark color

Ø  Off flavor: 

Ø  Zapatera sickness:

ü  Due to formation of caprilic acid and butyric acid by propionibacterium and clostridium .

ü  Since it occurs when pH > 4.2 , add acid to reduce pH<4 to prevent the sickness.

Q10. What are the bactofugation and thermisation?

Bactofugation is a high speed centrifugal process which separates bacterial cells and spores. This process is particularly important in Europe where problems arise due to spore formers such as Clostridium tyrobutyricum.

– Bactofugation removes 95% of the spores of milk which means the risk of late gas defect due to germination and growth of Clostridium tyrobutyricum is much reduced but not eliminated.

– 1-2% of milk solids is transferred to the bactofugate which, in particular contains casein along with somatic cells and bacteria.

– To avoid yield loss the bactofugate which contains 12-16% of dry matter, is sterilized by ultrahigh temperature processing and added back to the milk.

Bir cevap yazın