CL 420 Biochemical engineering
Course project (Bioindustry)
Mahesh Kumar Inakhiya
Date: April 13,
About the report:
Wine industry is important part of chemical engineering. An important process is Fermentation. Fermentation control in the winemaking process is critical for the production of wines having the correct aromatic and sensory quality. In this report, I have concentrated on control system of the wine making.
The wine industry has its own culture and it explains for many of the decisions made by wine makers. The industry is very slow to dramatic changes and this is reflective in the culture of the industry. To better understand the culture of the wine industry we must understand its rich history that heavily influences modern practices.
Wine has been a part of the diet of man since he settled in the Tigris-Euphrates basin and in Egypt several thousand year before our era. From these regions pre-christian traders carried the vine to all the Mediterranean countries. According to Vogt (1958) grape culture for wine production was known to the Assyrians and Egyptian by 3500 B.C. Greek traders brought grapes to Marseile by 600 B.C. and grape culture spread far down the Rhine by 200 A.D. and reaches its widest extension in Europe in the 15th century.
At a time when food was not the best, wine was an important food adjunct. During periods when life was often strenuous it offered relaxation and a very real surcease from pain. Wine thus became the normal table beverage of the Mediterranean countries, except for those where religion forbade its use.
Wine is the product of enzymatic transformation of the juice of berries of grape into a beverage containing alcohol. Originally, the fermentation was brought about by the natural yeasts attached to the surface of the ripe harvested berries . These yeasts comes in many different strains and ecotypes, each of which will produce a different assortment of by-products during the fermentation reactions, characteristic for the particular types of wine. Saccharomyces cerevisiae is the main species of yeast in wine making, although many other yeasts may be present at the start of fermentation . As fermentation proceeds, these other yeast species are strongly inhibited.
Modern wine makers prefer to introduce specially cultivated yeast strain, which help to guarantee the product they are aiming for. These yeast strains may have been selected for certain desirable characteristics such as resistance to high sugar concentrations . Nevertheless, some oenologists are disinclined to use selected yeasts contending that they may inhibit growth of apiculate yeasts present in the medium at the early stages of the process and hence hinder their potentially favorable effects on wine aroma.
The essential part of the wine flavor is formed during alcoholic fermentation. Ethanol and glycerol are quantitatively dominating alcohols, followed by higher alcohols and esters. Some higher alcohols may be present in concentration above their organoleptic perception threshold At concentrations bellow 300 mg/l they certainly contribute to the desirable complexity of wine; when their concentration exceeds 400 mg/l, higher alcohols are regarded as a negative quality factor. The main ester produced during fermentation is ethyl acetate. Other esters of fusel alcohols and short chain fatty acids, termed "fruit esters" because of their pleasing aroma, also appear. The fatty acid ethyl esters (ethyl hexanoate, octanoate, decanoate and dodecanoate) and long-chain higher alcohols acetates (isoamyl and 2-phenethyl acetates) are important. Their amount is below 10 mg/l, but this value is approximately 10 times their perception threshold.
Outline of the process: selected grapes of proper maturity are crushed and stemmed; treated with sulfur dioxide, or a sulfite, or pasteurized; and inoculated with a starter containing a pure culture of yeast. After a short fermentation period the wine is drawn off, placed in storage tanks for further fermentation, racked stored for aging, clarified, and packaged.
Details of the process.
1. The grape: the production of a fine wine may be regarded as commencing with the selection of the best variety of grapes for use in its manufacture. The quality of the grapes of a given variety will depend upon the condition under which they are grown –soil, climate, and other conditions.
Grapes should be gathered at the proper stage of maturity. In order to determine the degree of maturity , representative bunches of grapes are picked, and the Balling degree of their juice is determined. A reading of 21 to 23 O balling is usually given by the juice of the grapes when they are at the optimum stage of maturity.
2. Handling the grapes: in gathering the grapes and transporting then to the winery, the prime purpose should be to have them arrive in the very best condition possible. Careful supervision of the handling of grapes is essential.
3. crushing of grapes: Grapes are crushed and stemmed by machine. The chemical composition of the metal used in the construction of this machinery and other equipment about the winery is important. Iron and steel are used in some winery but are undesirable for they may cause clouding of wine , forming so called “ferric casse”. The tin and copper dissolved from bronze by grape juice, if sufficient in quantity, may cause flavor and color losses during the aging process. Stainless steel, nickel, or inconel should be used in preference to iron, ordinary steel, and many bronzes.
If the grapes are not picked when cool, it is desirable to permit them to cool overnight before they are crushed.
4. Treatment before fermentation: Grapes contain on their surface a varied flora of microorganism – molds, yeasts and bacteria. It is quite possible that the juice of crushed grapes will produce a good wine without any special precautions, but a wine manufacturer cannot afford to gamble in respect to the quality of his wine. He can do much to ensure the quality of his final product by destroying or inhibiting the development of the microorganism found on the grapes and by use of starters containing pure cultures of the specific yeast desired.
Sulfur dioxide or sulfites or inhibit the growth of many undesirable types of microorganism- acetic acid bacteria, wild yeasts, and molds- with a minimum amount of injury to the true wine yeast. Usually 2 to 6 oz. or twice the quantity of potassium metabisulfite, is added per tone of crushed grapes, the quantity used depending on the condition of the grapes- their maturity, the degree of contamination with molds, the temperature of the crushed product, an dothe rfactors. The largest quantities are used when the grapes are overripe, moldy, or relatively warm.
Pasteurization may be used in place of sulfites but is not usually considered to be so desirable.
5. The fermentation: The selection of a yeast, the nutrient substance in the must (grape juice), the concentration of the sugar, the acidity, the oxygen supply, and the temperature are factors that must be supervised in respect to fermentation.
S. cerevisiae var. ellipsoideus is the yeast used for the fermentation of must. selected strains, such as the Burgundy or Tokay strains, are frequently used. Many strains, bearing different names are known.
A starter is prepared from a pure culture of the selected yeast. Pasteurized must is used as the culture medium in preparing the starter, the magnitude of which should represent 2 to 5 percent of the crushed grapes being inoculated.
It is usually unnecessary to add any substance for the nutrition of the yeast since the crushed grapes are an adequate source of supply. On rare occasions ammonium sulfate or phosphate may be added.
The optimum concentration of sugar is 22O Balling. The use of much higher concentration of sugar favors the production of more than 13 percent of alcohol by volume. Since alcohol tends to inhibit the fermentation when present in concentration of 13 to 15 percent by volume, a maximum of 13 percent is usually desirable. The concentration that actually inhibits the fermentation depends in part on the temperature of fermentation, the tolerance of the yeast for alcohol decreasing with increasing temperature. The approximate concentration of the alcohol that will be produced in the wine can be predetermined by multiplying the balling reading of the must by 0.575.
It is permissible to reduce the concentration of sugar in must by the addition of water. Another practice is to mix the juice with the higher sugar concentration with a juice of low sugar concentration occasionally sugar may be added to must.
Grapes that have been permitted to become too mature are frequently of low acidity. Fruit acid- tartaric, citric, or malic acid- may be added to restore the normal acidity.
A large supply of oxygen is essential for the rapid multiplication of yeast cells and the starting of the fermentation, while the later stage characterize by alcohol and carbon dioxide production rather than growth proceeds best under nearly anaerobic condition.
Approximately 6 hr after the crushed grapes are treated with sulfur dioxide or sulfite, the starter is added. Thereafter the contents of the tanks are mixed, or stirred, at least twice a day, except during the main fermentation, to facilitate aeration, temperature equalization, and the extraction of color and tannin. Normally a “cap” forms on the surface of the fermentation vat, which contains grapes skins, pieces of stem, seeds, and other suspended matter. To mix the contents of the tank, one may punch down the cap or pump juice from the vat over the surface of the must.
The amount of aeration produced by mixing the contents of the tank is determined by the effectiveness of the procedure and by the frequency at which the operation is repeated. Provided that the fermentation is slow at the beginning, or near the end of the incubation period, the supply of oxygen may be increased by more frequent mixing of the contents of the vat. However, the must should not be overaerated during fermentation, for overareation is likely to produce a wine of inferior quality, especially in so far as color and flavor are concerned.
Fermentation should be carried out at carefully controlled temperatures. The finest wine are produced usually at a temperature below 85 oF (29.4 oC). The development of bouquet and aroma are favored by maintaining the fermentation must at a low temperatures, around 70 to 75 oF (21 to 23.9OC), for example. A temperature range of 70 to 90 oF is satisfactory. When the temperature rises to 85OF or at the most, to 90 oF are considered unsafe, while the fermentation is inhibited usually at a temperature of 97 to 100 oF. Fermentation cease at a temperature of 105 oF generally. Undesirable bacteria develop at the higher temperature. Accordingly the quality of the wine is impaired. Obviously, at too low temperature, the fermentation is too slow to be practical.
During the fermentation, records of the temperature and the Balling degree should be made at least twice a day, one set of observation being recorded on the side of the fermentation vat in order that the progress of the wine may be followed.
After 3 to 5 days of active fermentation, sufficient tannin and amaximum of color have been extracted from the skin of the grape. Extraction is facilitated by the agitation of pomace (skin, seeds, and pieces of stems) during fermentation, by the ethyl alcohol produced from the grape sugar , by the heat of fermentation, and by the mechanical breaking up of the skin.
The wine maker
decides when the color and tannin contents are satisfactory and then draws off
the wine to separate it from the pomace. He does not wait for all the sugar to
be fermented. At the time of drawing off the wine, the Balling reading may be 0
to 4o. It is not
considered advisable to mix the wine
drawn off (“free-run wine”) with that expresse
from the pomace, for the latter is of lower quality.
6. Further fermentation: The free run wine is placed in closed storage tanks, equipped with bungs that allow the excess carbon dioxide to escape. An atmosphere of carbon dioxide over the wine tends to inhibit the development of acetic acid bacteria and other aerobic types of microorganism. The fermentation sugar is usually consumed in 7 to 11 days at a temperature of 70 to 85 oF.
If the after fermentation becomes sluggish before the sugar is utilized, the yeast may be activated by pumping over the wine.
Control system for fermentation.
Wine fermentation has an isothermal fermentation rate that follows a consecutive reactions kinetic, depending mainly on fermentation temperature, original sugar content and total acidity of the must. Fermentation control in the winemaking process is critical for the production of wines having the correct aromatic and sensory quality. Control is also fundamental to minimise the energy consumption in the cooling systems of the wineries.
Fermentation control automation needs sensors to monitor fermentation evolution. Temperature has traditionally been used for control because it is easy to measure. However, temperature data do not provide any information about the evolution of the fermentation. It only establishes whether the fermentation is running in a safe state. The fermentation state can be identified by properties such as density, pH, differential pressure or CO2 evolution. In addition, the analysis of heat generation, called "exothermy", has been proposed for the brewing industry. These variables are generally difficult to measure on-line.
The production rate of CO2, as a control variable in fermentation, has received some attention in recent years, because production of CO2 is proportional to the quantity of sugar that has been fermented. It also has been demonstrated that the heat generated during the alcoholic fermentation process is related to microbial activity, and that is also related to other physiological variables, including the production of CO2.
Thus, it can be considered that modelling or measuring the sugar content, the density, the CO2 production or the heat generation is equivalent and that a model that can predict any of them can predict the others. Even if a model predicts one of them, or one of them is measured in a real process, all the others can be deduced.
i) Fuzzy control system
a). Non-isothermal kinetic model
By neglecting the mass losses by CO2 elimination, water evaporation, and ethanol and flavour losses in a fermentation tank, the general equation of a macroscopic energy balance in an open system at constant pressure, would be:
Where R is sugar consumption rate in the must, during fermentation: dS'/dt in g/h. dS'/dt=(dS/dt)·V, where dS is the decrease of the concentration in g/l and V the tank volume in l, H the heat formation during alcoholic fermentation (24/180 kcal/g, produced kcal by sugar consumed in g), Q heat exchanged with the surrounds, m the must mass in fermentation given by density (kg/m3) × V/1000(m3), Cp the specific heat of the must in fermentation, in kcal/kg °C and T the must temperature (°C).
This model has been used to develop the non-isothermal kinetic model of must fermentation, using a finite differences technique. This model predicts the relationship existing between temperature evolution and the amount of heat removed from the fermentation vessel, so it can be used to test new control techniques based, for instance, on temperature control, fermentation rate control or any other advanced control technique. It can also be used to optimise the use of any fermentation installation at industrial level, by providing the means to simulate a set of fermentation tanks.
A double-input single-output fuzzy controller is used in modern wineries, which uses fermentation rate and temperature measurements as inputs and the refrigeration action as an output. The control objective is to maintain a fermentation rate always lower than a certain level, since the higher the fermentation rate, the higher the flavour loss of the must.
There are two ways to build the control structure. The first way is to measure the fermentation rate (rate of sugar consumed by the process) by using a gas flow-meter, which measures the amount of CO2 being produced (which is proportional to the fermentation rate). The second way is to infer the value of the fermentation rate from the value of the temperature and the fermentation state using the fermentation simulator. So, instead of measuring the CO2 production, the fermentation rate is an output of the simulator that becomes an input for the controller.
The fuzzy rules are extracted by the knowledge of the process. Inputs to the controller are process temperature and error in the fermentation rate (defined as the measured rate minus desired rate). Process temperature (T) has three linguistic values: HIGH, NORMAL and LOW, and error in the process rate (E) had five: POSITIVE HIGH, POSITIVE, ZERO, NEGATIVE and NEGATIVE HIGH.
The output of the controller is the amount of refrigeration (R) required by the fermentation vessel, and has three linguistic values: HIGH, LOW and ZERO. Only three linguistic values are used, because the process is very exothermic and only refrigeration is usually needed at industrial scale.
There are only five control rules:
These rules can be explained as follows: (1)¯(4): if the process rate is too high, the vessel should be refrigerated to slow it. (5): if the temperature is too high and the rate is very low, the temperature will have to be lowered to avoid the reaction being stopped.
This rule set worked properly and made the system react as desired. For safety reasons, and in real applications, there are still two stop points, at 16°C and 22°C, that prevent the fermentation from going outside the normal band, although the fuzzy controller can avoid this problem. In addition, the fuzzy sets were adjusted to preclude temperatures (less than 16°C) that would inhibit the reactions.
As the isothermal fermentation rate has a maximum value that occurs between two and four days from the beginning of the fermentation, one could contrive to advance this moment by permitting the must to freely reach it by allowing the temperature rise naturally. When a certain fermentation rate is reached, it might be maintained by lowering the temperature until the must itself cannot sustain it anymore. Of course, the temperature has to be maintained between safe limits, typically between 16°C and 22°C, to ensure a correct fermentation process.
Although some people believe that higher fermentation temperatures in wine making lead to higher loss of flavour volatiles, others agree that it is caused by higher fermentation rates, which are related to higher fermentation temperatures. Thus, if the maximum fermentation rate is reduced, it can be presumed that the flavour losses during fermentation will also be lower. The main objective in this control system is then to set the fermentation rate at a certain level while the temperature remains between safe limits. The main effect is that the temperature is left to evolve freely until the fermentation rate set point is reached. Then the fermentation rate is maintained by refrigerating the tank until it starts to decrease.
Wine is usually racked when its density reaches a value of about 1000 g/l. This is a subjective decision, related to the fact that it happens when mostly all sugar has been transformed. But the reason to wait until this density value is reached is also related to a lack of knowledge on fermentation evolution. It would be possible to decide to rack sometime before reaching this density, when it is sure that the fermentation is so weak that the heat produced will not raise too much the temperature of the must. Criterion for racking is when the fermentation rate has reached the value at which an isothermally produced wine would have been racked (the fermentation rate corresponding to a 1000 g/l density). That value can be known by simulator . This criterion saves a lot of time and energy because the wine is racked before and no energy is used at the end of the fermentation, and there is no risk of stopping the refrigeration too early because the process evolution is known.
The reference values for temperature and fermentation rates are as follows: for every must, an isothermal fermentation of the same must should be considered as a reference process. An isothermal simulation of that process should be run, and the maximum value of fermentation rate should be noted. The temperature is usually 18°C (an isothermal fermentation temperature that is quite popular), and this is also the reference temperature. The reference rate should be set between 80% and 100% of the maximum rate for the isothermal process. This guarantees that the fermentation rate will be lower than the conventional one reached at constant temperature.
In some cases, depending on the must characteristics, these rules may have to be changed. However, the different runs of the simulator have shown that the rules work properly for most wine musts.
As can be seen in the figures, the controlled fermentation leads to a high energy saving (about 30% in some cases) and a high time saving (about 20%), thus leading to a higher productivity. By increasing the refrigeration use at the end of the process, the fermentation time can be reduced even more. The wine quality was not affected.
Fig. 1 shows the temperature evolution obtained with the fermentation rate based controller. It can be compared to Fig. 2, which shows the fermentation rate evolution in an isothermal vessel (thin line) and in a fuzzy controlled vessel (bold line). It should be noted that the final fermentation rate is the same in both cases, but it happens earlier in the fuzzy controlled tank.
Fig. 1. Temperature (°C) vs. fermentation time (h). The bold line shows the results of the fuzzy controlled process.
Fig. 2. Fermentation rate (g of sugar/l of must /h) vs. time (h). The bold line shows the results of the fuzzy controlled process.
Note that at the beginning of fermentation (first 15 h), the fermentation rate rises faster than in an isothermal fermentation at 18°C. This is what can be expected if the heat produced during the process is not evacuated, but used to heat the vessel, which is not refrigerated at this step. In this part of the process, no fuzzy rule is working.
Afterwards, as the fermentation rate reaches its maximum permitted value, the controller starts lowering the temperature so that it is maintained near its set point. Rules (1) and (2) dominate in this part of the process. If the temperature remained constant, a fermentation rate rise could be expected, due to the two consecutive reactions kinetic of the fermentation process. In this case, the fermentation rate would have had a shape similar to the 18°C isothermal fermentation shown in Fig. 2.
Then, the controller, dominated by rules (3) and (4), tries to compromise between a low temperature and a high fermentation rate, until about 70 h of process, when the reaction kinetics require a higher temperature to maintain the fermentation rate.
When the fermentation is nearly exhausted, the temperature is allowed to rise freely, while remaining between safe limits. It is in this part of the process that rule (5) works.
Fig. 3 compares the refrigeration consumption during the whole process. The dotted lines show the instantaneous refrigeration needs for a given must. In the isothermal vessel, refrigeration is needed during the whole process, while in the fuzzy controlled vessel refrigeration is used only after about the first 15 h. The main difference is a higher refrigeration peak that the refrigeration system has to be able to provide. This peak would cause problems if several tanks happened to be in the peak demand situation at the same time, but this can be avoided by correctly scheduling the fermentation process in the winery. The solid lines show the total refrigeration needs for fermentation. The fermentation time and refrigeration energy savings that are obtained by using the racking criterion already discussed can also be distinguished by comparing the values of the time and the total refrigeration energy use at the end of both graph lines.
Fig. 3. Total refrigeration consumption (kcal) vs. time (h) (solid lines) and instantaneous refrigeration power consumption (kcal/h) vs. time (h) (dotted lines). The bold lines show the results of the fuzzy controlled process.
Fig. 4 compares the density change in both cases. As can be seen, the density was higher at the end of the fuzzy controlled process, even if the fermentation rate was the same. Fermentation without temperature control will take the must-wine density to its final value, but without refrigeration use.
Fig. 4. Density vs. time (h). The bold line shows the results of the fuzzy controlled process.
Fig. 5 and Fig. 6 have been constructed in the following way: the maximum fermentation rate is measured (by means of simulation) for the same must in an isothermal fermentation (18°C). Then, several fuzzy controlled fermentations with different set points for the maximal fermentation rate are conducted. The maximal fermentation rates chosen vary from 50% to 140% of the maximal fermentation rate at 18°C.
Fig. 5. Total refrigeration consumption (kcal) (solid line) and fermentation time (h) (dotted line) vs. maximal fermentation rate (as a percentage of the maximal rate obtained at an 18°C isothermal fermentation).
Fig. 6. Maximum instantaneous refrigeration power consumption (kcal/h) (solid line) and maximum fermentation rate obtained (dotted line) (g ofsugar/l of must/h) vs. maximal fermentation rate (as a percentage of the maximal rate obtained at an 18°C isothermal fermentation).
In Fig. 5, the continuous line shows the total refrigeration consumption as a function of the maximum fermentation rate in an isothermal fermentation at 18°C. A minimum appeared between 86% and 94% of the maximum fermentation rate at 18°C.
The dotted line shows the total fermentation time as a function of the maximum fermentation rate. By comparing both figures, it can be seen that a maximum fermentation rate of 90¯96% of the maximum fermentation rate at 18°C nearly minimises time and refrigeration use.
In Fig. 6, the dotted line shows the value of the refrigeration power peak shown in Fig. 3 depending on the set point for the maximum fermentation rate. Note that the higher peak happened between 80% and 90%. This means the optimal total refrigeration use needs also a higher instantaneous refrigeration power.
The continuous line shows the actual maximum fermentation rate. Note that it does not vary linearly with the set point change. The reason is that the temperature is not allowed to go under 16°C, and so, if the chosen set point is under the maximum fermentation rate at 16°C, the fermentation rate is allowed to rise over the set point.
optimisation studies depend on the initial sugar content and the total acidity values of the must, so it should be repeated before every fermentation.
7. Racking: By “racking” is meant the drawing off the wine from the lees or sediment. Potassium bitartrate (KHC4H4O6), i.e., cream of tarter, is found in the less. This substance is less soluble in alcohol than in water and precipitates out more rapidly at low temperatures.
Wine is racked to facilitate its clearing and to prevent undesirable flavors being extracted from the old yeast.
8. Storage and aging: Two important changes take place during storage and aging: clearing of the wine and the development of flavor.
In a new wine there are present substance which, if not removed, will produce a sediment and probably cloudiness. These substances include tartrates, certain proteins, and other matter. Naturally these substances would be removed by racking and filtration during a somewhat long storage and aging process, but the modern trend is to hasten the removal of these substances by methods that involve flash pasteurization (to precipitate certain proteins), cooling to room temperature and then to 24 to 27 oF, and holding at the latter temperature for a few days. Filtration is carried out in the cold. Since the acid content of the wine is frequently reduced by the foregoing rapid process, it is customary to adjust the acidity with citric or tartaric acids, the former acid being preferred. The wine is placed in tanks for aging.
Wine storage tanks are generally constructed of white oak or redwood, white oak being the better of two. The tanks are completely filled with wine and sealed to prevent the access of large quantities of oxygen, which would favor the growth of acetic acid bacteria and C. mycoderma(wine flowers).
9.Clarification: wines may clear naturally over a period of time, but resort is frequently made to the use of finings followed by filtration, heating, refrigeration, or combinations of foregoing. Fining agents which include such substance as casein, gelatin and tannin, bentonite, isinglass, are mixed with the wine carefully according to direction. Filtration is carried out with filter aids.
10.Packaging: the clarified wine is placed in oak barrels for bulk sale and in bottles or in cans for unit sale.
Bottles of small and medium size may be pasteurized for 30 min. at 140 oF
Defects of wine: defects of wine may be caused by microorganisms., in which they are known as “diseases”. The disease of wine are of two general type: those caused by aerobic microorganism, and those caused by facultative anaerobes or anaerobes.
1.Defects caused by Aerobic microorganism. The aerobic diseases of wines are caused principally by mucodermas and acetic acid bacteria. These microorganisms grow well in the presence of oxygen. They are most likely to become active during the fermentation of must, if the cap is not punched down frequently, and during the storage wine, if the containers are not kept properly filled and sealed.
2.Defects caused by Facultative Anaerobes or Anaerobes. Tourne disease. the term “tourne” is to signify either the organism causing the disease or the condition produced in the wine by large numbers of these bacteria. Tourne is considered to be the most serious disease of wines and one of the most common.
The organism is an anaerobic bacterium, which occurs as long, slender rods. It may be found in any type of wine with alcohol content of 20 percent or greater. It grows best, however, if the alcohol concentration is not too great. Sugar and other nutrient substances favor its growth. It is inhibited by tannin but very strongly by sulfur dioxide and metabisulfites.
Tourne may be detected by a microscopic examination of the sediment, obtained by centrifuging a sample of the wine, or by analyses of the wine for volatile acids. Taste can also be of some assistance in its detection.
The judicious application of sulfur dioxide, 75 p.p.m., to wines, or pasteurization; the use of a high degree of cleanliness about the plant; sterilization of equipment with steam when necessary; rigid laboratory control should lower the incidence, or prevent, tourne disease of wine.
A pasteurization of bottled wine at a temperature of 145 oF for 30 min. is very effective in preventing tourne.
Once wine has been infected by tourne, it should be made brilliantly clear by filtration with selected infusorial earths, or by a clarification with bentonite followed by passage through germproof filters. Sulfur dioxide, or its equivalent of metabisulfite, should then be added to the wine in such quantity that its concentration will be maintained at 75 p.p.m., or greater. All equipment that has been infected should be treated with live stream or a suitable disinfectant to destroy th esource of infection.
3.Defects not caused by microorganisms: Defects in wines may be caused by metals, enzymes, and the improper use of certain fining agents.
Iron is a cause of clouding in wines. Two different types of defects are produced by iron (ferric casse, white casse). Only a few parts of iron in a million parts of wine will produce ferric casse. Using equipment constructed of the proper type of metal and inhibited by 0.1 percent citric acid can prevent this. White casse is also caused by an excess of iron. The treatment is outlined above for ferric casse.
Coating of wine tanks: concrete tanks are used for the fermentation of must and the storage of wine, but they must be lined to prevent an undue amount of calcium from being dissolved by the wine. Steel tanks should be lined to prevent the solution of iron.
1. Prescott, and Dunn; Industrial microbiology, Mcgraw-hill
2. Amerine M.A., Cruess W.V.; the technology of wine making
3. Martinez G., Lopez A., fuzzy control system for wine fermentation, Food control, Volume 10, Issue 3,June 1999,Pages 175-180