GB2094804A - Process for the production of a protein-containing product - Google Patents

Abstract

A process for the production of a protein-containing product comprises treating a colloidal suspension of protein-containing solids obtained as a by-product from a fermentation process such as pot ale or spent wash, with an alkaline reagent, preferably an aqueous solution of NaOH, KOH or NH4OH to adjust the pH to a predetermined value favouring flocculation and subsequent precipitation of the protein containing solids, and collecting the precipitated protein-containing solids.

Description

SPECIFICATION Improved process for the production of animal feed from by-products of whisky manufacture This invention relates to the production of animal feed from by-products of the whisky industry.

The major by-products of malt whisky manufacture are spent grains or draff and pot ale, the high boiling point residue from the distillation process. Wet draff and dried draff (light grains) have long been used for animal feed. Pot ale has in some instances been used as a fertilizer but is generally processed further by evaporation down to a syrup or completely dried to produce distillers dried solubles. In recent years the syrup has been added to wet draff and the mixture dried to produce distillers dark grains. The products because of their inherent high protein content have been acceptable to the animal feed compounding industry and have produced financial benefits for the distilleries.

The process for the production of such products is however, highly energy intensive and the rising costs of operating such plant is of major concern to the distilleries. The cost of running a multi-stage evaporator to concentrate the solids being of the order of two thousand pounds per week for a medium size distillery.

Supplies of pot ale are so large, in the region of 100,000 gallons per distillery per week, that if unutilized a serious disposal problem arises. The problem is compounded by the fact that the pot ale as an effluent exhibits a very high bio-chemical oxygen demand (B.O.D.) and may contain relatively high levels of metallic contamination. "Effluents from Malting s Brewing" by P.C. Isaac and G. Anderson. Journal Inst. of Brewing Vol. 79. 1973.

The high protein content of the solids in pot ale make them an attractive proposition for incorporation in animal feedstuffs, provided they can be recovered in an economic manner.

Increasing capital and operating costs of processing and drying plant are restrictive and the feasibility of continuing to use this equipment economically appears doubtful. Evaporators at present in use in the distilleries are estimated to cost 1 800 per week to run of fuel alone to produce pot ale syrup at 40% dry matter. The present invention proposes an alternative low energy process for the concentration and recovery of the valuable solids from the pot ale byproduct of the distillery process. Assuming all distillers use such a process for concentration, the potential energy savings of the process of this invention are considerable.

Pot ale is the liquid residue that remains in the first (wash) still. The distillate enters a second (spirit) still from which the final product is condensed, leaving spent lees as the liquid residue.

At some distilleries the pot ale and spent lees are combined together and called pot ale and this may also be further diluted by water used for washing equipment. Pot ale will therefore differ in character and composition between distilleries.

Pot ale consists largely of suspension of dead yeast cells in a colloidal solution. Amino acids, polypeptides, minerals, vitamins, fusel oils and unfermented carbohydrates are also present. The significant amounts of yeast and lactic acid bacteria contributes to riboflavin, thiamine and pathothenic acid. The amino acid content is comparable to dried yeast and large amounts of arginine, histidine and lysine are a result of yeast synthesis. The nutritive quality of the solid would be high and balanced if the product was supplemented with a methionine rich food such as marine products.

Characteristics of a typical pot ale pH 3.5 Dry Matter 25% Crude Protein 30% B.O.D. 1000 1006000 mg/litre Copper Content 5 mgrams/kg Characteristics of a resulting pot ale syrup after evaporation pH 3.5 Dry Matter 40% Crude Protein 30% Cu 65o120 mgram/kg Price 45 per Tonne The strongly acidic nature of the pot ale and syrup has obvious disadvantages for incorporation in feedstuffs and for disposal as an effluent.

In addition pot ale solution exhibits the characteristics of a lyophobic sol which presents difficulties in recovery of solids since they are suspended in a colloidal state.

A discussion of the problems associated with flocculation of colloidal yeasts may be found in "Effect of Some Monovalent and Divalent Ions on the Flocculation of Brewers Yeast Strains" by G. G. Steward and T. E. Goring. Journal Inst. of Brewing Vol. 82. 1 976.

An object of the present invention is to obviate or mitigate the aforesaid disadvantages and thus provide a more economic process for effective utilization of pot ale.

According to the present invention there is provided a process for the production of a proteincontaining product comprising treating a colloidal suspension of protein-containing solids obtained as a by-product from a a fermentation process with an alkaline reagent to adjust the pH to a predetermined value favouring flocculation and subsequent precipitation of the proteincontaining solids, and collecting the precipitated protein-containing solids.

Preferably the process comprises treating a solution of pot ale with a solution of NaOH, KOH, or NH40H to achieve a pH I within the range of from 6 to 10, adding a flocculating aid to the solution, allowing the flocculated solids to precipitate under the influence of gravity and separating the precipitated solids from supernatent liquid in conjunction with mechanical separation to obtain a protein-containing product of at least 20% dry matter, preferably by centrifugation.

Advantageously the pH is adjusted to a value of from 7 to 9, most preferably a value of 8.2.

Preferably also the flocculating aid is added to the solution of pot ale before addition of the solution of potassium or sodium hydroxide. This allows fluctuations in the pH created by the addition of the flocculating agent to stabilize and thus allow a more accurate monitoring of the required pH adjustment to achieve the predetermined pH value at which flocculation and precipitation is likely to occur.

Any known flocculating aid comprising a di- or multi-valent cation may be used but hydroxides of the alkaline earth metals or first transition series metals are preferred. Of these calcium hydroxide is the most preferred for this process.

In a start-up procedure the pH required for the raw pot ale is determined as follows.

A laboratory analysis of the sample from this solution is carried out to determine the optimum pH for flocculation and precipitation of the suspended solids.

100 mls of the raw pot ale is titrated against 5% NaOH and a standard inflexion curve of mls of NaOH against pH is plotted.

The linear plateau of this curve is found to lie within the range of pH 7.25 to 8.65. 1 7.4 mls of this 5% NaOH solution were required to achieve the optimum pH of 8.2. Thus 0.87 9 NaOH were required to neutralise 100 mis of pot ale.

The precipitated slurry contained 5.5% solids and resulted in a total recoverable dry solids yield of 3 g from the 100 ml sample.

In a preferred embodiment of the process a 9000 litres batch of raw pot ale solution containing 2-5% suspended solids and having a pH value of 3.4 is run into a tank provided with an agitator.

Calcium hydroxide is added in an amount of 1 g/litre of pot ale with vigorous stirring until complete dissolution is achieved and the pH is monitored continuously.

After stabilization of the pH 0.08 tonnes of sodium hydroxide in two solution strengths were added; a) concentrated NaOH solution as main pH raiser to overcome buffer action of initial solution, b) dilute NaOH solution for fine pH adjustment to achieve a pH of 8.2 + 0.5, with continuous agitation and pH monitoring.

The agitator is switched off when the pH remains constant for a period of time and the solution is allowed to settle for several hours.

Thereafter the settled solids are drained off and the supernatant liquid is passed to a biological effluent treatment plant.

The settled solids are further reduced by mechanical separation techniques to aproximately 20% dry matter.

The solids thus obtained may be incorporated in animal feedstuffs according to conventional processes.

An improvement on the above may be achieved by utilizing the high temperature of the pot ale to assist the flocculation and precipitation. This will result in a shortening of the settling time.

Other flocculation agents to achieve electrolytic charge neutralization at a particulate level may be used, bearing in mind that they may have an effect on the final composition of the product with regard to toxicity to live stock.

Advantages of this process are that the solids obtained may be separated at 20% dry matter or better as per the original process and in a readily marketable form. The pH of the product will be about 8.2 which is approximately neutral for feed purposes. The effluent will probably exhibit a substantial bio-chemical oxygen demand as total dissolved solids will be of the order of 2-3%.

Although sodium and calcium levels in the product will probably be raised, this should not be significant for use in animal feedstuffs.

Whilst the above describes the application of the process to a by-product from a malt whisky distillery, the process as defined will also have application to by-products produced as the result of similar industrial fermentation processes. It is considered that the 'process' as developed for malt distillers could have an application for similar problems in the Scotch Grain Whisky industry. The scale of operation of such distilleries is significantly larger than the batch production operations in the malt distilleries, and they therefore offer greater financial potential for the 'process'. Preliminary tests on the by-products of a Scotch Grain Distillery have been undertaken.

The basic differences between Malt and Grain Whiskies lie in the nature and proportion of the cereals used as raw materials and the type of still used in the distillation process. Scotch malt whisky only uses one cereal malted barley, but in Bourbon, Canadian, Scotch grain and Irish Whisky other cereals are used along with the malted barley, to provide the additional starch in the mash. Malt Whiskies are usually produced in a batch process, while other whiskies are generally produced by continuous distillation techniques. Some distillers filter their worts from the mash before fermentation, but others, especially in North America, ferment the whole mash, i.e. ('in grains' fermentaton).

Scotch malt whisky is produced in a number of relatively small distilleries, about one hundred.

The brands which are not straight malt whisky are marketed as a blend of malt whiskies with another type of whisky produced in Scotland called Scotch grain whisky, or because it is distilled continuously in a Coffey-type patent still, patent-still whisky. Most Scotch whiskies available on the international market consist of blends with 30-40% malt whisky. Within the blend, there may be as many as 20-30 individual malt whiskies and grain whiskies.

The cereals used in the manufacture of Scotch grain whisky are malted barley along with a high proportion (up to 90%) of maize (called corn in North America) and occasionally some rye.

Scotch grain whisky is manufactured in a continuous distillation process.

In such a process, the raw material Maize, is ground and cooked under pressure. A limited quantity of malted barley (approx. 4 wt. of Maize feed) is added to provide the necessary enzymes for hydrolysis of the starch to simple carbohydrates. The resultant Mash is passed to the Mash Tun wherein the temperature and pressure are lower and the bulk of the conversion of the starch occurs here.

The contents are optionally filtered to separate out the Wet Draff or the whole contents is cooled and fed to the fermenter. Yeast is added and the fermenting Wash is fed to the Distillation columns which comprise a wash column and a rectifying column in series. The Raw Whisky is recovered from the top of the rectifying column and spent wash is collected as a bottoms product from the wash column.

The spent wash is comparable with the pot-ale produced in Batch processes. It is somewhat more dilute, continuous production giving approximately 9.5 gallons spent wash per gallon proof compared with approximately 5 gallons pot-ale per gallon proof in a batch process.

The spent wash could therefore be regarded as dilute pot-ale. Incidentally whereas 'spent wash' is terminology used in the Scottish art, it may be equated with the term 'thin stillage' used by others in the art to describe the liquid effluent remaining after the separation of bulk solids from 'whole stillage' i.e. that portion containing 'distillers solubles'.

In general spent wash has a solids content of approx. 3.6% before screening and 2.5% after of which 2/3 are considered to be dissolved whilst the balance are suspended.

The pH of this spent wash is from 3.3 to 3.8 and the biochemical oxygen demand (B.O.D.) after screening amounts to about 10,000 p.p.m.

In the past this has been subjected to concentration by evaporation, neutralisation and spray drying to 3% moisture to give Distillers Dried Solubles (D.D.S.).

According to the process of the present invention the spent wash is treated with an alkaline reagent to adjust the pH to a predetermined value favouring flocculation and subsequent precipitation of protein containing solids suspended therein thus allowing the solids to be separated and collected.

The preferred pH range for spent wash is from 5.5 to 9.5 Preferably Ca(OH)2 is added at 0.1% weight for volume to initiate flocculation and once the pH has stabilized, the pH is further adjusted if necessary to lie within the preferred range.

The pH adjustment is preferably accomplished by the addition of Na OH solution at 10% weight for volume.

Advantagously the process is carried out with continuous agitation and pH monitoring.

After a suitable time period the agitator may be switched off and settling allowed to occur.

The solids are collected and treated as for those resulting from the treatment of pot-ale and the effluent is passed to a bio-treatment plant or alternatively to an evaporator.

It is to be expected that in the treatment of spent wash, less chemicals will be required for pH adjustment due to the smaller difference between the optimum pH for precipitation and the pH of the raw spent wash.

It is also anticipated that this process may be applied effectively whenever fermentation/distillation processes are used for spirit production.

To determine the optimum pH I for flocculation and precipitation of the suspended solids in a raw spent wash, 100 mls of the raw spent wash is titrated against 4% NaOH and a standard inflexion curve of mls of NaOH against pH is plotted.

The linear plateau of this curve is found to lie within the range of pH 5.5 to 9.5. 4.2 mls of this 4% NaOH solution were required to achieve the optimum pH of 8.2.

On this basis 100,000 gallons of spent wash would require 1/2 tonne of Ca(OH)2 plus 0.763 tonnes of NaOH solution to yield 1 2.5 tonnes (est) dry matter (a yield of approximately 2.5%).

Thus, in comparison with the calculations for pot-ale above, a 9000 litre batch of spent wash would only require 0.01 5 tonnes of NaOH instead of around 0.08 tonnes.

In a pilot plant set-up, 1 250 gallons of pot ale treated according to the process of this invention yielded 143 kg of solids after gravitational settling and decanting. The settled solids were reduced by mechanical separation to 19.3% dry matter, of which 50% was protein.

This compares favourably with an estimated yield for 1 00% dry matter of 28.2 kg, the actual yield being 27.6 kg.

Claims (17)

1. A process for the production of a protein-containing product comprising treating a colloidal suspension of protein-containing solids obtained as a by-product from a fermentation process with an alkaline reagent to adjust the pH to a predetermined value favouring flocculation and subsequent precipitation of the protein containing solids, and collecting the precipitated protein-containing solids.

2. A process according to claim 1 wherein the alkaline reagent is an aqueous solution of NaOH or KOH or NH4OH.

3. A process according to claim 1 or claim 2 wherein a flocculating aid containing at least one di- or multi-valent ion is added to the suspension.

4. A process according to claim 3 wherein the flocculating aid is a hydroxide of an alkaline earth metal or a first transition series metal.

5. A process according to claim 4 wherein the floculating aid is calcium hydroxide.

6. A process according to any one of claims 3 to 5 wherein the flocculating aid is added to the suspension before addition of the alkaline reagent.

7. A process according to any one of claims 1 to 6 wherein the suspension is agitated and the pH thereof is monitored throughout the process.

8. A process according to any one of the preceding claims wherein heat resulting from a distillation process is used to assist flocculation and precipitation.

9. A process for the production of a protein-containing product comprising treating a solution of pot ale with a solution of NaOH, KOH, or NH40H to achieve a pH within the range of from 6 to 10, adding a flocculating aid to the pot ale solution, allowing flocculated solids to precipitate under the influence of gravity and separating the precipitated solids from supernatent liquid in conjuction with mechanical separation to obtain a protein-containing product of at least 20% dry matter.

10. A process according to claim 9 wherein the pH is adjusted to a value of from 7 to 9.

11. A process according to claim 10 wherein the pH is adjusted to 8.2.

12. A process according to any one of claims 9 to 11 wherein flocculating aid is added to the solution of pot ale before addition of the solution of NaOH, KOH or NH4OH.

1 3. A process according to any one of claims 9 to 1 2 wherein the flocculating aid is calcium hydroxide.

14. A process according to any one of claims 9 to 1 3 wherein the high temperature of the pot ale issuing from the distillation process is used to assist flocculation and precipitation.

1 5. A process for the production of a protein-containing product comprising treating a solution of spent wash with a solution of NaOH, KOH or NH40H to achieve a pH within the range of from 5.5 to 9.5 adding a flocculating aid to the spent wash solution, allowing flocculated solids to precipitate under the influence of gravity and separating the precipitated solids from supernatent liquid in conjunction with mechanical separation to obtain a proteincontaining product of at least 20% dry matter.

1 6. A process according to claim 1 5 wherein the pH is adjusted by addition of a 10% (w/v) solution of NaOH to the spent wash solution.

17. A process according to claim 1 5 or 1 6 wherein the flocculating aid is Ca(OH)2 which is added in an amount of 0.1% (w/v).