Field of the invention

The invention relates to yeast, the production thereof and its use in bakery products.

Background of the invention Yeast is used in the manufacture of many baked products to leaven doughs and batters. "Leavening" occurs when yeast produces CO ₂ gas, resulting in the formation of bubbles or pockets of gas within a dough or batter. This provides the baked product resulting from leavening with a lightened, softened or sponge -like texture.

Yeast may be manufactured commercially by inoculating a series of fermenters of successively increasing size. The first few are mildly aerated batch fermentations. In these stages, conditions are such that ethanol will be formed. Generally the last two (or sometimes three) stages are performed using full aeration and incremental feeding with an energy source such as molasses.

These fed-batch fermentations may be carried out in fermenters of 100 m ³ (and more) net volume. Fermentation time is typically in the range of 12-20 hours, in which some 20,000-30,000 kg of fresh yeast is produced. After the feeding with substrates has stopped, aeration is usually continued at a reduced level to let the yeast cells attain maturity and uniformity.

Further processing includes separation from the broth by centrifugation and washing which results in cream yeast (17-23 wt% dry matter content). The cream yeast may be processed into compressed yeast (27-33 wt% dry matter content) or dried yeast (92-97 wt% dry matter content).

Compressed yeast is produced by dewatering the cream yeast with either rotary vacuum filters or filter presses. Compressed yeast requires refrigeration for storage. An average storage life for such yeast is 2 to 3 weeks, after which the yeast loses its leavening qualities, its bacteriological content tends to increase and the cells begin to autolyse. The reduction in volume compared with cream yeast allows for more efficient and simplified transport, and because the yeast cells in compressed yeast are still fully hydrated, they activate quite quickly once added to a dough. Compressed yeast is therefore best suited to smaller users with access to refrigeration.

Compressed yeast can be extruded and dried to produce active dry yeast or instant dry yeast with moisture contents of 6-8 wt% and 3-6 wt%, respectively. Dry yeasts are used in the bakery trade because of their extended stability and the absence of any need for refrigerated storage. However, dry yeasts lose part of their leavening activity during the drying process as well as during the dehydration procedure, and have a restricted shelf- life once the pack is opened and the vacuum is released.

Given these limitations of compressed and dried yeast, particularly in larger industrial plant bakery applications there is a preference for using cream yeast. Cream yeast can be delivered and handled in bulk and dosing at the mixer can be easily automated. However, one problem with cream yeast is the phase separation that can occur in the cream yeast tanks during transport and storage if constant agitation is not applied. It has been found that a liquid yeast suspension shows a perceptible yeast concentration gradient in a vertical direction within 6 hours. This is understood to be a consequence of yeast cells having a higher density than water, so that the cells gradually sink to the bottom of a container (phase separation). In the long run a 'clayish' suspension is formed on the bottom which is difficult to resuspend with the remaining liquid.

Phase separation is a concern, particularly for automated baking processes, as dosing of yeast can become inconsistent. In the circumstances, where progressive batches of dough or batter might receive the same volume of cream yeast, there is a risk that each batch will receive different amounts of yeast. The result is inconsistent leavening from batch to batch.

One approach for dealing with the problem of phase separation includes the use of a stirrer for maintaining a dispersion of the yeast so that settling and phase separation cannot occur. The dispersion could also be maintained with a pump that withdraws part of the yeast cream from a container and subsequently reintroduces it into the container so as to effectively re-circulate the yeast cream. These approaches involve complicated apparatus and regular cleaning to minimise infection of the yeast.

Other approaches are to add an additive such as a plant-derived, or microbial-derived gum (EP0461725) or a homopolysaccharride, in particular starch (EP0792930) to the cream yeast. One limitation of these approaches is that some countries require these additives to be identified whereas most manufacturers of baked products would prefer to be able to minimise the number of additives recited on product labelling or packaging. Another limitation is that these additives are essentially another input cost that the yeast producer or baker has to absorb or pass onto the consumer.

There is a need for new formulations for leavening dough, batter and related baked goods in which phase separation of yeast is minimised.

Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.

Summary of the invention

In one embodiment the invention provides a composition for leavening a dough or batter, the composition including water, yeast and a dough conditioner in the form of an emulsifier, the emulsifier being provided in an amount to increase the viscosity of the composition thereby minimising phase separation of yeast in the composition.

In other embodiments, there is provided a process for producing a composition of the invention including the steps of combining yeast with a dough conditioner in the form of an emulsifier and optionally water, the emulsifier being provided in an amount to increase the viscosity of the composition thereby minimising phase separation of yeast in the composition. In other embodiments there is provided a use of composition according to the invention for leavening a dough or batter. These embodiments may include steps of:

- providing a tablet, capsule, granule or similar unitised quantity including one or more enzymes, oxidants or other ingredients for modifying components present in a dough or batter;

- releasing the enzyme, oxidant or other ingredient from the quantity into a mixture of ingredients for forming a dough or batter;

- contacting the composition according to the invention with the mixture in conditions for leavening a dough or batter formed from the mixture. Further, these embodiments may include a step of combining the yeast and emulsifier and optionally water or salt to form the composition of the invention.

In other embodiments there is provided a process for producing a baked good including:

- contacting a mixture of ingredients for forming a dough or batter with a composition according to the invention in conditions for leavening a dough or batter formed from the mixture;

- baking a leavened dough or batter formed from the mixture to produce a baked good. These embodiments may include the step of combining the yeast and emulsifier and optionally water or salt to form the composition of the invention.

In other embodiments there is provided a baked good produced by a process according to the invention.

Detailed description of the embodiments

The inventor has found that an emulsifier can be used to disperse, and/or suspend yeast, and that this composition can be used, optionally in combination with additives, in place of conventional bread improvers. The present invention seeks to provide a composition for leavening a dough or batter, the composition including water, yeast and a dough conditioner in the form of an emulsifier, the emulsifier being provided in an amount suitable for minimising phase separation of yeast in the composition.

An "emulsifier" is a substance or combination of substances commonly used in dough conditioners ("dough conditioners" are sometimes known as "bread conditioners" or "bread improvers"). In these applications, these emulsifiers are understood to effectively strengthen the dough and make it more extensible. This may result in trapping more gas in smaller bubbles, reducing proofing time and giving a softer, more even-textured bread with brighter crumb colour and improved keeping qualities. The added "stretch" can also make the dough more tolerant to over- or under-mixing. Some other emulsifiers combine with starch in the flour in ways that prevent over-firming and staling so that the bread remains softer for a longer period of time. Some have an effect of producing a more crispy crust that retains its crispness qualities longer.

One advantage of the composition of the present invention is that it makes the dosing of yeast in a baking process easier. As discussed previously, phase separation of yeast can occur during storage or transport, resulting in a solution which does not have an even concentration of yeast cells throughout. Thus, agitation of the yeast mixture is required to achieve even dispersion of the yeast cells. The addition of emulsifier according to the invention can stabilise a dispersion of the yeast to form a suspension and thus prevent phase separation of the yeast. This produces an even distribution of the yeast throughout the mixture, making addition of a known amount of yeast easier to achieve, without the need for agitation.

Another advantage of the present invention is that the amount of emulsifier required to be added to achieve a given functional effect, is less than that used in conventional dough conditioners. This is believed to result from the fact that the hydrated form of the emulsifier allows for a more rapid and better dispersion of it within the dough during mixing. A yet further advantage of the present invention is that gums or other additives no longer need to be added, which also results in a reduction of the cost of the dough preparation process. This finding is a significant departure from the teachings of the art. In particular, as far as the applicant is aware, all prior art has taught the use of additives (EP 461725, WO 02/49441 , EP 619947, EP 792930, EP 461725 and WO 06/046146). Further, WO 03/048342 discusses combination of yeast with processing aids. Notably in all cases additives such as gum are used. Accordingly, in another embodiment of the invention, the composition of the present invention does not include gums or other additives selected from the group consisting of xanthan gum, guar gum, modified starch, a plant-derived gum, a microbial-derived gum, and a homopolysaccharride.

As discussed above, fewer ingredients results in cheaper input, purchase and transport costs, and this signifies an important advantage of the present invention over conventional bread improvers.

Additionally, soy flour, fillers and gums, which are often present in powdered conditioners, generally may not contribute to bread quality, but are often required to be included in the list of ingredients on labels of products containing them. The omission of these additives from the dough conditioner thus makes labelling more attractive to consumers, and allows for a reduction in formulation, packaging and production costs.

According to the preferred aspects of the present invention, emulsifiers are selected from the group consisting of DMG (distilled monoglycerides); mono- and diglycerides, esters of mono- and diglycerides; polyglycerol esters of fatty acids; polyglycerol polyrincinoleate; propylene glycerol esters of fatty acids; sorbitan monostearates; sorbitan tristearates; SSL (sodium stearoyl lactylate); calcium stearoyl lactylates; and

DATEM (diacetyl tartaric esters of mono/diglycerides). Preferably, the emulsifier is SSL, or combination of SSL with other emulsifiers, in particular DATEM.

The inventors have also found that the amount and type of emulsifier in relation to the yeast is important for minimising phase separation. In the case of SSL, quantities between 1 - 5% provide good stability, and viscosity increases with increasing addition. Other emulsifiers have different effects on viscosity and stabilisation of the mixture. Phase separation in the context of the present invention refers to the sedimentation of the yeast cells, which leads to an inhomogeneous yeast stock and 'minimising' can mean any of reducing, diminishing, lessening, curtailing or decreasing the phase separation of the yeast cells.

Preferably, the emulsifier is provided in an amount of from 1 to 20%, 2 to 15% or 3 to 8% w/w of the composition.

It has also been found by the inventor that the amount of emulsifier used depends on the type of emulsifier. For example, when using SSL a considerable increase in viscosity occurs at levels of addition as low as 1% and in fact a solid product can be obtained at levels above about 10%. In contrast, DATEM provides a much lower viscosity increase and forms a less stable emulsion, and is best used in combination with another emulsifier like SSL. The skilled addressee in following the teachings herein will be able to determine the correct amount of each emulsifier to use to achieve the objects of the present invention. Principally, the objective is to ensure that the mixture is pumpable and yet will not separate on standing. As a guide, SSL is preferably used in an amount from 1 - 8%; DATEM is preferably used in an amount from 1 - 10%; and DMG is preferably used in an amount from 1 - 10%. The viscosity may be measured by standard means known in the art, including the use of a viscometer.

In a preferred embodiment the composition of the present invention has a dry matter content of 20%. Generally, the major component by weight is water with the weight of water being 75%. In other embodiments the composition has a weight of water as low as 60%, however to achieve reduced levels of water, salt may need to be added in order to maintain the required viscosity. The salt draws out the intracellular water into the extracellular space, and the water can then be removed by, for example, filtration, or by other methods known in the art. As noted above, by "required viscosity", it is meant that any given mixture is not so viscous that it cannot be pumped, but sufficiently viscous to avoid separation on standing. In one embodiment the yeast .dry weight is that of cream yeast (17-23% dry matter content), although it will be understood that this is in no way limiting on the proportion of yeast that may be used.

Further, it is also possible to manipulate the ratio of yeast to water i.e. decrease the weight of added water by adding salt to the yeast. The advantage of this is that the yeast composition has a dry matter content that is higher than normal cream yeast and comparable to or even exceeding the yeast dry matter content of compressed yeast (27 to 34%). Thus, it combines the advantage of traditional compressed yeast (high yeast dry matter content) with the advantage of traditional cream yeast (ease of operation). Thus, the yeast used in the composition of the present invention may be derived from compressed or dry yeast and can be obtained by processes known in the art.

Another variation on this is that salt can be added to a yeast solution to decrease viscosity at a given addition of emulsifier. This result is achieved because intracellular water is drawn out of the cell, effectively diluting the extracellular contents.

Another variation allows for the production of a composition in the form of a compressed yeast. SSL or other emulsifiers can be added to the cream yeast prior to increasing the solids content by filtration or other means to allow the production of compressed yeast. This option provides functional benefits in the baking process and greatly simplifies improver formulations.

A further variation allows the composition in the form of compressed yeast to be dried to produce a dried yeast with a high functional level of emulsifier.

Additionally, other emulsifiers may be added if particular characteristics of the loaf are desired, which cannot be provided by the emulsifier used to prevent phase separation. Examples include glycerol monostearate (GMS), bile salt, triglyceride, fat or lecithin.

The composition of the present invention may include, in addition to an emulsifier and yeast, a processing aid in the form of an enzyme, an oxidizing agent, an antioxidant, a reducing agent, a gum, an oil, or starch. The additives may be added to improve the handling properties of dough and/or the final properties of the baked products. Dough properties that may be improved comprise machineability, gas retaining capability, among others. Properties of the baked product that may be improved comprise loaf volume, crust crispness, crumb texture, softness and shelf life. The composition may also further include a gum or starch.

In the context of the present invention the yeast is Bakers Yeast, which relates to living yeast cells such as from the genera Saccharomyces, kluyveromyces, Torulospora, in particular Saccharomyces cerevisae or Torulaspora delbrueckii. The term also comprises combinations of one or more yeast species optionally with other microorganisms such as lactic acid bacteria. Preferably the yeast is baker's yeast or Saccharomyces cerevisae.

Yeast for use in the present invention can be made using any of a number of techniques well known to those skilled in the art. In accordance with the present invention, compressed yeast (which has a dry matter content of 27 to 34%) can be used but water is generally added to the compressed yeast to decrease the percentage of dry matter content to that typical of the level exhibited in cream yeast (17-23% dry matter content). It follows that if the yeast is not compressed, water does not need to be added to the yeast.

Another way of decreasing the dry matter content in compressed yeast is to add salt to the yeast. This draws out the intracellular water, which effectively dilutes the extracellular contents, thus decreasing the percentage of dry matter content in the yeast,

According to the present invention, the emulsifier is essential for minimising phase separation of the yeast. The amount of water in the yeast can be regulated, as discussed in the preceding paragraph by techniques known in art, prior to adding the emulsifier. This includes adding water to the yeast, removing excess water by centrifugation, or removing intracellular water and replacing with extracellular water using salt, as discussed above. It has been discovered by the inventors that the amount of water or salt added to the yeast is important. It determines how much emulsifier is required to be added to the yeast to produce a dispersed yeast mixture that is in accordance with the present invention.

Production of the emulsifier/yeast mixture can be done in a number of ways, using either batch or continuous processing. An exemplary flow chart is shown in Figure 1. Using a batch process, emulsifier is added to an agitated vessel containing cream yeast at the required level of addition. The contents of the vessel are then recirculated through a high speed homogeniser or emulsifying pump until the contents have thickened to the required viscosity. When the added emulsifier is in powdered form, best results are obtained when it becomes fully hydrated and no visible particles of powder remain. Additional components such as oil, oxidants, enzymes, etc can be added with the emulsifier, although it is generally preferred that they are incorporated using medium to high speed agitation after the composition has been produced.

Continuous production requires a more intense emulsifying action as the end result needs to be achieved in a single pass. Required ingredients are fed in accurately controlled quantities directly into the chosen mixer with a similar quality output obtained to that produced on a batch system. Depending on requirements, continuous production may be done using a series of more than one mixing stage.

At this point, other additives, such as those exemplified above, may be added to the leavening composition. However, in some embodiments, this defeats some of the advantages of the present invention.

It may be useful to test for yeast function e.g. gassing ability, before the emulsifier is added, and optionally after the additives discussed above have been added. If the activity of the yeast is found to be acceptable, the emulsifier may be added. It should be understood that it is not necessary to agitate the composition to disperse the yeast after the emulsifier has been hydrated in the composition although in other embodiments a further step of agitating the yeast to affect dispersion may be included. In one embodiment, dispersion of yeast cells occurs as the emulsifier is hydrated (for example by adding emulsifier to the extracellular water of the yeast cream) to increase viscosity of the composition.

Exemplary processes according to the present invention are shown below in the Examples. The key aims of the process are to stop the emulsion/yeast mixture from getting too hot, minimise disruption of the yeast cells and achieve full dispersion of the emulsifier in order to enhance functionality and stability. The preferred result of the process is that a smooth, creamy, stable consistency is obtained, and in embodiments where other ingredients are incorporated, these are uniformly dispersed and remain so for the shelf-life of the product. However, in accordance with the present invention, it is not necessary that all yeast cells are dispersed, as long as it is possible to accurately dose in the given application.

In the context of the present invention, the term 'dispersed' is used to describe when yeast cells are diffused, spread, disseminated and distributed and/or where the mixture of yeast cells and other ingredients is homogeneous.

It follows that the yeast cells, once dispersed, will remain suspended in the composition to the extent required to achieve the advantages of the present invention. That is, the yeast cells will not settle out of the composition to a substantial extent for the shelf-life of the product.

Examples

Example 1 Production of leavening composition of the invention.

In certain embodiments of the present invention, the emulsifier needs to be thoroughly solubilised within the water containing the suspended yeast cells. In the case of liquid emulsifiers this may be possible using relatively simple low to medium speed mixing. With powdered emulsifiers, considerably more intense mixing is required. For laboratory trials this is done using a high speed homogenising mixer such as an IKA Ultra-Turrax or possibly even a domestic stick type mixer. For larger scale production trials, an emulsifying pump or similar high intensity mixer is required to solubilise the emulsifier within the cream yeast.

While the addition of emulsifier to the yeast can be done at a number of points in the yeast production process, the preferred location is following the completion of the brew, either before or after standardisation of activity. Table 1 summarises typical blends of ingredients. The laboratory Blend 1 was prepared by adding the powdered SSL to the cream yeast and homogenising using a Sunbeam Stick Mixer model SM6200 on speed 2 for 2 minutes. The end point was determined by an increase in viscosity and an absence of visible emulsifier lumps in the blend. Powdered ascorbic acid was then dissolved in the smooth, thickened liquid. Vegetable oil was then added with mild agitation, and resulted in an oil in water emulsion, which remained stable for the 14 day duration of the yeast's functional shelf-life.

Table 1 : Ingredients of Blend 1 and 2

Standardised SSL (g) Ascorbic Vegetable oil (g) Salt (g) cream yeast (g) acid (g)

Blend 1 1000 50 2 100 0

Blend 2 1000 100 3 100 20

Blend 2 shows a variation where salt is added to the product in order to reduce viscosity resulting from a higher addition of SSL. Example 2 Phase separation minimisation

Minimisation of phase separation is achieved by the increase in the viscosity of the composition, which occurs with the hydration of the emulsifier.

Table 2: Blend viscosity

Blend 1 : Cream Yeast 1000 + SSL 50 + Oil 100 Blend 2: Cream Yeast 1000 + SSL 50 + Oil 200

Table 3 summarises changes in viscosity at increasing levels of SSL in cream yeast with both the addition and absence of 20% oil. Clearly as the level of SSL increases, the viscosity of the solution increases for all treatments, although this becomes particularly marked at levels of addition above 2%. With the addition of 20% oil there is a further slight increase in viscosity.

Table 3: Impact of SSL concentration on viscosity

Example 3 Use of leavening composition in a baking process

Bread produced in most parts of the world contains a trio of 'essential' ingredients, flour, salt, yeast, and a number of 'optional', but widely used ingredients which may include fat or oil, soy flour, gluten, emulsifiers, ascorbic acid or other oxidant and enzymes. By including oil, emulsifiers and ascorbic acid at the required levels with yeast in a combined product, this invention greatly simplifies the addition of these components at a bakery. Further, the addition of a number of these components in a more readily dispersed form, allows for either improved quality attributes or a reduction in the quantity required in the formulation to achieve a given level of performance. This applies particularly to the levels of oil and emulsifier required.

Table 4 demonstrates that improved loaf volume and levels of softness can be obtained using reduced levels of oil and emulsifier when incorporated in the format outlined by this invention. Total levels of yeast (5% on flour weight), oil (1%), SSL (0.25%) and all other ingredients in the formulation were kept constant for each trial with the only variable being the method of delivery. Softness was measured using a Stable Instruments TA-XT2 texture analyser with peak resistance measured using a 36mm diameter probe after a 10 mm depression into the crumb. Lower resistance figures indicate better softness.

Table 4: Summary of softness levels

Volume Day 1 Day 2 Day 5 softness softness softness

Cream yeast 2350 259 374 601

Blend 1 2400 205 324 542

Blend 2 2425 181 299 480 Blend 1 : Cream Yeast 1000 + SSL 50 + Oil 100 Blend 2: Cream Yeast 1000 + SSL 50 + Oil 200

While it may be possible to include some enzymes in the composition of the invention, a preferred option is to provide the enzymes separately by way of either a tablet, or some other form of single unitised delivery which may include a capsule, granule or other non dusting entity, which can be accurately dosed, either manually or automatically. One option is to provide all enzymes combined in the form of a single composition tablet. An even more preferred option is to separate enzymes into functional activities, (e.g. softening enzymes, volume enhancing enzymes, whitening enzymes etc). This option would allow the bakery to add only the required levels of those enzymes needed to suit individual products, thus minimising costs, allowing product differentiation and optimising product quality. This variation is illustrated in the flow chart in Figure 1.

In larger bakeries, where higher levels of automation are used, tableted enzymes could be automatically counted, weighed or otherwise dosed into a mixer or preferably into the dough water prior to mixing with a very high degree of accuracy.

It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.