CA1228767A - Packaging of baker yeast - Google Patents

Abstract

A B S T R A C T

A totally sealed and slightly inflated package containing granular, free flowing fresh baker's yeast having excellent physical and biochemical preservation characteristics. A process for the production of the same comprises the steps of selecting a plastic laminate for the package that is totally or practically totally impervious to oxygen,carbon dioxide and water vapor, filling the package with yeast containing less than 70% moisture and sealing the package in a manner so as to totally or almost totally prevent the inclusion of any significant volume of air. The sealed package is subjected to time and temperature conditions under which a desireable volume of carbon dioxide is generated in situ through auto-fermentation. The time and temperature conditions have no deleterious effect on the leavening activity of the yeast.

Description

The present invention concerns the packaging of bakers yeast and aims at providing packages of such yeast, e.g., in free flowing form, in which when stored under refrigeration the yeast retains essentially its physical and leavening characteristics over extended periods of time.
Yeast which is to be used for baking purposes is a product based on any of the strains of the species Saccharomyces cerevisiae. There are many strains of yeast that are included within this species, differing from each other, among others, in osmotolerant characteristics, ability to ferment various sugars, resistance to dehydration, etc. A yeast product based on any of these strains is produced commercially in a series of fermentations or stages. The yeast is grown under aerobic conditions by the addition of large volt uses of air to the growth media. Carbohydrates, in the form of molasses, and nitrogen sources, in the form of ammonia, are continuously incorporated into the growth media, especially in the last stages of propagation. The phi temperature and solute concentration of the growth of media are maintained within ranges where optimum growth the yeast occurs. At the conclusion of the last propagation stage, the yeast is separated from the other dissolved ,.

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constituents of the growth media by centrifugation and a number of washing cycles. Yeast at this stage, at about 204 solids content, is a tan colored liquid and known in the art as liquid or cream yeast. Cream yeast is converted to a plastic or solid consistency by vacuum or other filtration procedures. Such yeast product is known in the art as compressed yeast containing approximately 30~ solids and may be molded or extruded into blocks or cubes in which form it is supplied to bakers or for household use.
Another form of yeast product provided to the baker is bulk yeast. This product, almost always at a solids level substantially above 30%, is granulated and provided to the baker as is or treated with a minor amount of drying agent intended to preserve the free flowing characteristics of this type of yeast.
Still another yeast product available to the consumer is referred to in the art as active dry yeast.
The initial processes involved in the production of this product are those described for compressed or bulk yeast production, a Saccharomyces cerevisiae strain known as Boos No. 23 being generally used. The issue classification is as per publication by Schultz and Akin in "Archives of Biochemistry", Vol. 14; p. 369 (August 1947). Prom a suitable compressed or bulk type yeast product obtained from this strain, active dry yeast is obtained by any of several processes known in the art. or example, the compressed yeast can be converted into spaghetti form and dried on a moving belt under controlled temperature and time conditions.
Fresh, compressed or bulk yeast is sold principally to bakeries. The household consumer has two types of yeast products available to him. They are fresh compressed yeast packages or cubes, wrapped in aluminum foil, or active dry yeast, packaged in air, vacuum, or under inert gas conditions.

3'76'7 The fresh compressed yeast cube, known in tile art as Household Yeast, is distributed as a refrigerated item. This product has a shelf life of about 4 to 6 weeks under storage conditions generally referred to as cool and dry. To achieve this kind of storage characteristics the yeast has to undergo special treatment in all stages of its preparation, especially before filtration and packaging. Also, the packaging material generally an expensive aluminum foil laminate has to be especially treated to minimize the tendency of mold development on the surfaces of the yeast cube. This kind of product, being in cake or block form, has the additional disadvantage of having to undergo dispersion before it can be added to the flour in home baking. The product suffers also from other shortcomings such as loss of weight and discoloration if not properly wrapped.
The development of an active dry yeast product came against the background of the disadvantages exhibited by the household yeast package, and aimed at providing a better product. And indeed the active dry yeast type product has a longer shelf life and has no mold or discoloration problems. The active dry yeast has, however, other inherent problems. For one, it is less active than fresh yeast. Moreover, it has to be dehydrated under controlled temperature convictions before it can be used in the baking process, and this can become a major burden to the consumer when attempting to bake yeast leavened goods in a kitchen. Additionally, to achieve a reasonable room temperature shelf life, the yeast may have to be packaged in expensive material such as aluminum foil laminates under inert gas conditions When adding to this the cost of a very demanding drying procedure, there results a very expensive product for the household consumer.
It is thus seen that both of the two kinds of commercially available yeast products have serious drawbacks and are far from satisfactory.

Bakers yeast, e.g. free flowing, fresh bulk yeast, would be an ideal product for, among others, the household consumer. For the consumer to enjoy all the possible benefits of such a product it would have to come to him in a package which ensures for the yeast the following characteristics:
1. A reasonable stability to rough handling.

2. A relatively long refrigerated storage stability.

3. Retention of physical properties, even under stacking or pressure.

4. No discoloration of the product due to partial drying or oxygen contact.

5. Total or near total prevention of so-called respiration, i.e. stop the penetration of oxygen into the package.

6. Protection of the yeast product from mold development and reduction to a large extent of the invasion of contaminating microorganisms.

7. Preservation to a large extent of the initial leavening activity of the yeast product.
B. Ready availability in a form in which it can be added directly to the flour without requiring a cumbersome resuspending stage that is necessary with the household cube or active dry yeast products.
Bakers yeast is, however, a potentially problematical product. It comprises a mass of living yeast cells having varying amounts of extra-cellular water in the interstitial spaces between and surrounding the cells. Water is also the largest component of the yeast cell and is referred to as intracellular water. The feel or appearance of compressed or bulk yeast is largely determined by the relationship between the intracellular and extra cellular water in a particular yeast product PI

preparation. Obviously, the relative dryness or wetness of a yeast product will affect the tendency of the yeast to stick or coalesce and therefore cause a deterioration in its free flowing characteristics.
Bulk yeast, being in a fine granulated form, provides a relatively large surface area for atmospheric oxygen to interact with the yeast. The process is called respiration and its results are the generation of water, heat, and other products. It is this generation of extra water during handling and storage that can ultimately partially or totally destroy the free flowing characteristics of the yeast product. US. Patent No. 4,232,045 provides a partial remedy to this problem.
It teaches the incorporation into the granulated yeast of a drying agent that will tie up some of the water that may be generated by the process of respiration. A
bulk yeast produced by the teaching of that patent will indeed have an improved capacity to retain free flowing characteristics over extended periods when packaged in especially designed polyethylene lined bags and held under refrigerated conditions. Because of the nature of the package, respiration occurs however, end ultimately sufficient water is generated, overland above the absorption capacity of the drying agent, leading to a reduction of the free flow capacity, discoloration, and loss of leavening activity. A similar approach is also disclosed in laid open German patent specification No. 26 19 348.
In British Patent No. 966,984 a partial solution is provided to tackle the respiration aspect of granular (bulk yeast. In accordance with the teachings therein granular yeast is packaged in polyethylene (or similar material) which slows down the rate of oxygen penetration into the bag while permitting carbon dioxide generated in consequence of respiration and auto fermentation, ~.2;~7~'7 to diffuse Jo the outside. Pro better carbon dioxide discharge a special OpeniJ1g is provided in the bag.
It has, however, turned out that in practice oxygen still finds its way into the yeast, resulting in respiration or generation of water.
The problem of respiration could not be solved by simply packaging yeast in hermetically sealed containers or under any other anaerobic conditions, thereby to prevent penetration of oxygen, since the prior art teaches that strict anaerobic conditions are detrimental to the packaged yeast product. Thus, in the book "The Yeasts"
(S. Burrows - 1970), in the chapter dealing with the keeping quality of compressed or bulk yeast it is stated, among other things, "oxygen and carbon dioxide concentrations in the immediate vicinity of the resting cells appear to be of considerable importance ...". It is further stated that granulated compressed yeast is difficult to store and that " ... a certain amount of ventilation appears to be necessary, possibly to allow a reduction in carbon dioxide by diffusion.". Furthermore, from a paper presented by ~ajamaki Factories of the State Alcohol Monopoly, Alto, Finland, at the Yeast Symposium held in-France in 1978, it follows that anaerobic storage conditions are very deleterious to the quality of the yeast as compared to better quality if oxygen is present during storage.
In accordance with the invention there is provided a method of preparing a packaged yeast product, wherein fresh free-flowing bulk yeast is introduced into a pliable bag whose oxygen permeability at 1 elm. pressure differential across the material does not exceed about 1000 cm3/m2 per day and whose carbon dioxide permeability at 1 elm. pressure differential across the material does not exceed about 4000 cm3/m per day, the amount of yeast in the bag being so dosed that the bag is not full to capacity, the so filled bag is sealed hermetically and is then left 6'7 a-t a temperature within the range of 0-20C to enable -the occurrence of auto fermentation without affecting deleteriously yeast quality thereby to produce carbon dioxide and inflate the bag.
As a result of the inflation there develops a carbon dioxide protective cushion around the grant-fated bulk yeast. In this way the yeast is protected against rough handling and squeezing during trays-partition and storage, whereby the free flowing properties of the yeast are retained.
Preferably, air present in the head space of the bag is expelled as far as possible by squeezing before the bag is sealed.
Upon the completion of the inflation the yeast in the sealed bag is under what may be termed anaerobic conditions characterized by the presence of mainly a carbon dioxide atmosphere. As already explained above, the prior art teaches that yeast may not be stored under anaerobic conditions since under such conditions the leavening capacity is significantly reduced. The prior art further teaches - see for example British patent specification No. 966,984 and "The Yeast" by S. Burrows referred to above - that carbon dioxide must be continuously removed from stored yeast. It was therefore completely surprising to discover in accordance with the present invention that by storing fresh, free flowing bulk yeast in sealed bags under a carbon dioxide atmosphere, the yeast retains essentially its free flowing character-is tics and its leavening strength for extended periods of time.
The degree of inflation of the bag that is required for the purpose of the present invention is not critical as long as it is sufficient to produce a protective cushion as specified. In practice, full inflation of the package is as a rule not required For example, in a package configuration of 1 g of yeast to four volumes of _ _ _ {l I Jo 6'7 package size, it will be quite sufficient to generate only 2 ml of carbon dioxide per gram of yeast. For the generation of such relatively small amounts of gas it is as a rule not necessary to warm the packaged yeast above the packaging temperature and it is sufficient to cool the yeast down to storage temperature - as a rule about 5-10C - at such a rate that sufficient carbon dioxide develops.
The degree of inflation is obviously directly affected by the rate of auto fermentation by the yeast, which in turn is dependent on the temperature of story age. Thus, any particular yeast strain grown under a particular set of propagation conditions, to a specific nitrogen and phosphorous content, will have a predict table and known auto fermentation profile at a given temperature. It is accordingly possible to alter any of the above to produce a yeast that has a suitable auto fermentation profile.
The art also teaches other ways by which one can affect a change in the auto fermentation profile of a particular yeast product Thus, the treatment prove-dune described in US. Patent 4,008,335 is quite suit-able for the purposes of the present invention.
The handling temperature during the pack-aging will as a rule be within the range of 10-20C
and the cooling down period may typically be from 24-48 hours.
There is no criticality as to the relative proportions between the volumes of the bag and the pack-aged yeast. In this context volume of bag means the volume of water required to fill it to capacity when empty, and weight ratios of yeast to bag volume of 1:27, have been found to produce satisfactory results. How-ever, such packaging would be wasteful and as a rule a weight ratio of yeast to bag volume = 1:4-1:6 is preferred.

5~7~;i'7 g The material used for making pliable bags whose permeability to oxygen and carbon dioxide is as specified can be of any kind -that is inert to the pack-aged product. For example, bags made of plastic polyp ester sheets, possibly reinforced with small amounts of polyethylene, may be used to advantage. Other examples are bags made of polypropylene or aluminum foil, and there are of course many others.
Typical plastic material sheets produced by Kibbutz Negba, Israel, have the following permeably-ties:
Gas Permeability (cm3/m? day, bar*) Oxygen Carbon dioxide Polyethylene 1,700 8,500 Polypropylene 1,000 3,500 Polyester 100 450 * "bar" stands for a pressure difference of 1 elm.
It follows from these data that polyethylene is unsuitable for the purposes of the present invention while polypropylene and polyester are suitable.
As explained above, hitherto household consul mews had at their disposal only either compressed yeast or active dry yeast and either of these products have their inherent disadvantages, the cubes or bars of come pressed yeast having to be first dispersed in Waterloo the active dry yeast has to be dehydrated prior to use for which specific conditions have to be strictly observed. Free flowing bulk yeast is free of all these disadvantages but hitherto had the disadvantage of having a relatively short shelf life even under refrigeration so that hitherto it could only be used in bakeries.
The invention provides for the first time free flowing bulk yeast for household use packaged so as to have, when stored under refrigeration, a relatively long shelf life of 3 months or even more.

2~'76~7 Quite generally, the present invention pro-vises maximum storage stability that any particular yeast may have. Thus, for example, i-t is possible in accordance with the invention to store and preserve bakers yeast for household use which hitherto has not been possible.
The invention is illustrated in the following Examples without being limited thereto.
Example 1 This example describes the profile of a par-titular yeast as regards its potential to produce car-bun dioxide by auto fermentation and to the leavening activity by the yeast product upon storage for differ-en periods without refrigeration.
The yeast was propagated under normal condo-lions to a composition of about 42~ total protein (Kjeldahl) and 1.90~ POW. After centrifugation and washing, 300 liters of cream yeast were treated with 20 liters of a saturated sodium chloride solution.
The treated liquid yeast was vacuum filtered to about 34 per cent solids, granulated through a plate contain-in 2 millimeter diameter holes, and treated with four per cent Aerosol 200 on a weight basis (a trade mark of Degas A of the Federal Republic of Germany).
The packaging was in a polyethylene reinforced polyester laminate of about 0.06 mm total thickness.
The actual formation of the packages, filling and heat sealing was by hand. The sealed package containing 20 g of free flowing yeast was at about 18C when the test series was started. The volume of the package when empty (as measured by the volume of water that it could hold) was about 550 milliliters. Table I sum-marines the results.

., .

'76'7 Table I
Initial --Temperature Carbon dioxide Activity Days of of storage generated retained, 5 storage average). .cc/gr %
.. _ _ .. _ _ . . . _ .. .. . _ 1 17.8 4.4 100.0 12 17.8 7.7 86.2 16 19.4 12.4 77.7 19.4 13.8 55.4 23 20.0 18.0 42.4 Example 2 Yeast was propagated, filtered, treated with Aerosol 200, and packaged as under Example 1. Two package sizes, one of 170 milliliters volume and the other of 550 milliliter volume, were willed each with 20 grams of free-flowing, fresh baker's yeast. The results are given in Table II.

Tubule * Leavening Activity ** Package Size . .
milliliters 550 milliliters Fresh 1945 1945 After 3 months at * Volume of carbon dioxide produced in two hours in a flour dough containing initially 10% added sugar.
** The size refers to the empty package when filled with water. In actuality, the package designated as "170" had only a total volume of 70 milliliters;
while the package designated "550" had a total volume of 128 milliliters after two weeks at 5C
(as measured by immersion of sealed yeast package in water and determining the total volume of water displaced). These relative volumes did not change on further storage at 5C.

I

Example 3 This example compares the stability of the package produced in accordance with the invention to the stability of a package that had a pun pro-vision for the diffusion of carbon dioxide to the out-side according to the teachings of British Patent No.
966,984.
The yeast was propagated as in Example 1, but this time to a protein composition of 41.9% and POW of about 1.70%. The filtered yeast contained about 34.7% solids. After treating with 2% Aerosol 200, the yeast was packaged in polyethylene-polyester film as in Example 1, but this time in a package that contained 25 g of free-flowing yeast in a total package lo volume of about 100 milliliters. The yeast was package Ed on a commercial packaging machine supplied by Rouse of Barcelona, Spain, model 1214 T. The yeast packages were stored at 15-20C and the observations made after 14 days of storage are recorded in Table III.
Table III
Activity retained %. Flow property Start fresh) 100 Free flowing After.one..week..
. _ _ Sealed package 100 Free flowing Pin-hole in package 79 Formation of . small lumps After.two.weeks Sealed package 90 Free flowing Pin-hole in package 57 Gummy consistency It is seen from the data in the table that the flow properties upon packaging and storage in accordance with the invention are significantly superior to those according to British Patent No.
966,984.

Example 4 This example illustrates the potential of storage stability that our invention may impart to free-flowing, fresh baker's yeast under various -temperatures.
The yeast was propagated and treated as under Example 3 and stored under the various storage condo-lions as listed in Table IV. Before storage, the temperature profile of the yeast during preparation 10 and packaging was:
After filtration and extrusion 13C
After treatment with Aerosol 14 C
After two days at 0C yin bulk) 2C
After packaging and handling 17C
The storage series started with the yeast being at 17C and having generated about one ml of carbon dioxide per gram of yeast at this point.
Table IV
Activity retained - %
20 Days of storage Storage temperature - C
lo 15 20 Example 5.
.
This example illustrates the superiority of a polyester laminate over polyethylene which has inherently a certain degree of permeability to oxygen and carbon dioxide.
The yeast was propagated, filtered, treated with Aerosol 200, and packaged as under Example 1.
Two types of packaging materials were compared.
Polyethylene film alone was compared to a laminate of ' 'I' I

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polyester. In the first case 20 g of free-flowiny, fresh baker's yeast was sealed in a polyethylene package with a potential volume ox about 170 ml., the polyethylene being of 0.05 mm thickness. In -the second instance, 20 g of similar yeast was sealed in a polyp ester laminate with a potential volume of 5S0 ml., the laminate being of 0.06 mm total thickness. No attempt was made to squeeze the head space air out before heat sealing. In both cases the temperature history of the yeast was identical and thus:
Extruded yeast 13C
After treatment with Aerosol 16C
After packaging 18 C
The storage started at 18C and was at room conditions in a temperature range of 15-20C. The results were:
After 12 days at 15 to 20C
Polyester Polyethylene laminate _ Activity retained, 57 88 20 Appearance Gummy with Free-flowing putrid odor and fresh smelling Example 6 This example compares the permeability characteristics of three different plastic materials in terms of the degree of head space inflation of the yeast package as a function of storage temperature.

Jo f~7~7 Table V
StorageInflation.of Available Head Space - %
Temperature Packaging Material and Time ...... Polyethylene Polypropylene Polyester 5 Attica . . .
2 months 0 8 31 Attica 5 days 14 24 83 10 days 0 20 97 1017 days 0 20 burst open Attica 2 days 19 44 59 3 days 22 52 90 5 days 3 44 burst open 157 days 19 64 burst open It is seen from Table V that polyethylene is unsuitable because it allows the COY generated by the yeast to readily escape to the outside.

Example .
This example compares the results obtained upon storage of yeast in polypropylene and polyester bags in accordance with the invention.

Table VI
Polypropylene Polyester Activity Activity Days.at.16C retained,.%. retained, %
.. ...

'I
"I, Jo ,cV,2~ '7 Example 8 . . .
This example compares -the results obtained in accordance with the invention with two kinds of yeast.

Table VII
* Inflation.- %
Type of Yeast Days Attica Untreated Treated **

7 burst open 69 - * A polyester laminated package, with an available volume of about 240 ml, was heat sealed with about 50 grams of yeast in it.
** Treatment of liquid yeast, prior to filtration and further handling, was as per US. Patent 4,008,335.

Example 9 This example shows the leavening activity of yeast packaged in accordance with the invention in bread dough formula after different storage times at 5C.

Time.of.storage at 5C Activity retained, %
. _ . _ . . . _ . . .
4 months 87 25 5 months 84 6 months 74 ,.~.~,

Claims (13)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Method of preparing a packaged yeast product, comprising the steps of introducing fresh, free-flowing bulk yeast into a pliable bag made of a material having, at about one atm. pressure differential across the material, an oxygen permeability not exceeding about 1000 cm3/m2 per day and a carbon dioxide permeability not exceed-ing about 4,000 cm3/m2 per day, the yeast being intro-duced into the bag in an amount such that the bag is not filled to capacity, hermetically sealing the thus-filled bag, and leaving the thus-sealed bag at a temperature in the range of about 0-20°C, whereby autofermentation of the yeast produces carbon dioxide which forms a protective cushion about the yeast, and inflates the bag so that the auto-fermentation does not deleteriously affect the yeast quality.

2. A method according to claim 1 additionally comprising expelling air from the head space in the bag by squeezing prior to sealing.

3. A method according to claim 1 wherein the ratio between the weight of the yeast in the bag and of water filling the bag to capacity as a measure for the bag volume is within the range of about 1:4 to 1:6.

4. A method according to claim 1 wherein said material of the pliable bag is a polyester laminate.

5. A method according to claim 1 wherein said material of the pliable bag is polypropylene.

6. A method according to claim 1 wherein said material of the pliable bag is aluminum foil.

7. The method of claim 1, wherein the thus-sealed bag is left at a temperature of about 5-10°C.

8. The method of claim 1, wherein the yeast is introduced into the bag at a temperature of about 10-20°C, and then cooled for about 24-48 hours.

9. The method of claim 1, wherein the thus-sealed bag is left at the temperature for at least about three months.

10. A packaged yeast product, comprising a pli-able packaging formed of a material having, at about one atm. pressure differential across the material, an oxygen permeability not exceeding about 1,000 cm3/m2 per day and a carbon dioxide permeability not exceeding about 4,000 cm3/m2 per day, and containing said yeast, whereby autofermentation of the yeast produces carbon dioxide which forms a protective cushion about the yeast and inflates the packaging so that the autofer-mentation does not deleteriously affect the yeat quality.

11. The product of claim 10, wherein said yeast is fresh, free-flowing yeast.

12. The product of claim 10, having a shelf life of at least about 3 months when stored under refri-geration.

13. The product of claim 10, wherein the packaging is hermetically sealed.