BUTTER-BOXES AND MOULD-GROWTH.

New Zealand Journal of Agriculture, Volume 53, Issue 3, 21 September 1936, Page 129

BUTTER-BOXES AND MOULD-GROWTH.

W. Riddet,

Dairy Research Institute, and J. C. Neill, Plant Research Bureau, Palmerston North.

Mould - growth on the surface of stored butter is unattractive to the buyer and injurious to the butter. It has been shown by several investigators that mould fungi can grow well on the surface of both salted and unsalted butter, and Vernon (i) has demonstrated that they may develop in the interior of unsalted butter, although generally they are limited to the surface layer of salted butter. Surface mould seldom makes its appearance until stored butter has been defrosted. The origin and control of mould is therefore of great importance to manufacturers of butter, especially in countries (such as New Zealand and Australia) distant from their principal markets, because butter made over a considerable period may be affected before this happening becomes known to the makers. The sources of infection have been variously attributed to butterboxes, parchment, and aerial contamination of the butter during manufacture. Vernon(i) has shown that butter-box timber and parchment-paper can be the source of moulds and can support mouldgrowth. Neill(2) has confirmed Vernon's observations with regard to timber, and he has also shown that the treatment of timber with a solution of the sodium salt of salicylanilide, sold under the trade name of “ Shirlan W. S.” is effective in preventing mould-growth on butterbox timber. The part played by butter-boxes is of great significance to the New Zealand butter industry. Three types of boxes — standard, substandard, and sawn-timber Saranac (wire-bound)are used for exporting butter. The design of each is defined in the New Zealand Dairy Regulations (3). Until recently Saranac boxes made of rotary-cut timber were also employed, but their export has been prohibited since Ist January, 1936. The first three named boxes are made of sawn timber, which may be either air-dried or kiln-dried. Rotary-cut timber differs radically from the sawn in two respects. Prior to peeling, the logs are subjected to a treatment with high-pressure steam which enables the knife to shear off the cut timber in “ peelings ” of any desired thickness. The peeled timber is then straightened by passing the pieces between hot rollers, being dried to a definite moisture content. The timber is next cut into required sizes and assembled into wire-bound boxes. The economy of this.process by the elimination of saw-dust is obvious.

In addition to differing in design, the boxes differ in the thickness of timber employed in their construction. The ends of both the standard and sub-standard box are made of timber f in. in thickness. The sides,.top, and bottom of the standard are made of | in. timber, while the corresponding parts of the sub-standard are made of f in. The ends, sides, top, and bottom of the Saranac wire-bound box are made of | in. timber. White-pine timber is most extensively used, but silver-beech and Swedish pine, impregnated with wax, are also employed. Experimental. The following two series of experiments were carried out to determine {a) the relative resistance of different types of butter-boxes to mould-growth ;. (&) the effect of heavy infection of box-timber with mould spores ; (c) the extent of damage caused by surface mould ; and (d) the practicability of protecting butter from mould-growth originating from the box. In the first series, objectives (a), (&), and (c) were studied. The second was undertaken to provide confirmatory evidence of the first and to test on a semi-commercial scale the effectiveness as a fungicide of Shirlan W. S. Fifty-six-pound boxes of the various types under trial were packed with salted butter at a nearby butter-factory. They were then held in cold storage at 13 0 F. for nine days, and, after being defrosted in a room kept at an average temperature of 68° F. and from 85 per cent, to 90 per cent, relative humidity for a period of a week, were examined individually for mould-growth. Prior to being stacked for defrosting, each box was dropped several times from a height of about 3 ft. to the floor to simulate handling in transit. This treatment caused the sides of some of the boxes to spring” from the ends. Care was taken in stacking the boxes to expose all types to approximately the same conditions. First Series. Seventeen boxes were employed, five being standard, two substandard, five Saranac made of sawn timber, and five Saranac made of rotary-cut timber. . Prior to being filled with butter, two of each of the standard, sawn Saranac, and rotary-cut Saranac types, and one sub-standard, were sprayed inside and outside with a mixed suspension of spores from pure cultures of Pullaria pullulans, Cladosporium herbarum, and Penicillium expansum, and thereafter lined with a double fold of 28/30 lb. parchment-paper. One standard, one sawn Saranac, and one rotary-cut Saranac were first similarly infected with mould spores and thereafter lined with parchment-paper, also sprayed with the same suspension of mould spores. The remaining boxes were not artificially infected. The boxes were filled with salted butter, stored, defrosted, “ dumped,” and examined as described above. RESULTS. (a) Non-infected Boxes. — The standard and sub-standard boxes were free from visible mould-growth. Black-spot (Cladosporium) and greenmould {Penicillium) developed in scattered areas on the outside and inside of the sawn Saranac boxes, on the parchment lining, and on

parts of the surface of the butter. Internal mould-growth was most prolific at those points at which the sides had “ sprung ” from the cleats of the boxes. The rotary-cut Saranac boxes showed much heavier mould-growth, the exterior, interior, and parchment-paper all being affected. A little mould penetrated to the surface of the butter. The predominating moulds were Cladosporium, Penicillium, Mucor, and a red staining type. As in the case of the sawn-timber box, mould-growth was most profuse in areas adjacent to openings between the sides and ends. A significant feature of the mould on both types of Saranac box was its dense growth on panels made of soft, sappy timber, those made of heart timber being comparatively unaffected.

(b) Infected Boxes. — As was to be expected, all of the inoculated boxes developed more mould - growth than the non-inoculated, the intensity of infection varying with the type of box. That on the standard and sub-standard was limited to areas adjoining seams (Fig. i) in the sides of the box ; no mould penetrated to the surface of the butter at these places. The sawn Saranac boxes showed more extensive growth of mould on the exterior and interior and on the parchment - paper, especially at the seams and edges. Some mould penetrated to the butter. The rotary-cut Saranac boxes were even more extensively

covered with moulds, as also was the surface of the butter. In all casesPullaria predominated, but the Cladosporium and Penicillium were also present. Boxes lined with infected parchment developed no more mould than those not so treated. Furthermore, no mould developed, from infected parchment under those parts of boxes not affected with mould-growth. Second Series. The same types of boxes were employed, with the addition of (a) standard and sub-standard boxes made of Swedish pine and (&) sawn Saranac boxes made of f in. white-pine. Provision was also made toinvestigate the possibility of preventing the growth of mould on the boxes by treating them with a solution in water of sodium salicylanilide (Shirlan W. S.), and to' determine whether a lining-material made of aluminium foil sandwiched between two sheets of parchment-paper would prevent mould from penetrating to the surface of butter from badly-infected timber. It has already been shown that this latter material prevents the development. of surface yellow colour on butter by avoiding the evaporation of moisture (4).

The ten Swedish pine standard boxes were impregnated with wax. while four of the sub-standard were not waxed. The Shirlan-treated boxes were immersed in c-i per cent, solution of Shirlan W. S. for ten minutes, the standard and sub-standard boxes being treated in the shook, and the Saranac type in the wire-bound but open state. Subsequent to treatment, the boxes were air-dried. The infected boxes were sprayed with a suspension of mould spores as in Series I, the Shirlantreated boxes being sprayed subsequent to treatment. The parchment was not sprayed. The boxes were packed with salted butter, stored,, “ dumped,” and defrosted in the same way as the first series. As in Series I, the sides of several of the | in. Saranac boxes sprang from, their ends whilst being “ dumped.” The f in. Saranac boxes remained intact. Some of the standard and sub-standard boxes had split sides see plates 2 to 4.. There was no visible appearance of mould-growth on. any of the boxes prior to storage nor on immediate removal from the.cold store.

RESULTS. The following table shows the relative extent of mould - growth ■observed in the various butter-boxes :

The non-infected standard (Fig. 2) and | in. Saranac (Fig. 4) whitepine boxes developed only a small amount of mould-growth which did no material damage to the butter. The sub-standard (Fig. 2) and | in. sawn Saranac (Fig. 3) developed more extensive growth, which penetrated to the butter near openings in the boxes. In several cases more mould was observed inside the box than on the exterior. The untreated rotary-cut Saranac boxes were heavily covered with mould, and in the stack stood out clearly from the others (Figs. 3 and 4). The untreated Swedish-timber boxes were quite free of mouldgrowth (Fig. 5). Infection of the timber with mould spores accentuated the degree of moulding in all cases previously affected and induced mould-growth on some of the Swedish boxes. The growth on the inoculated boxes was general, while that on the non-inoculated was localized (Fig. 7). The non-infected Shirlan-treated boxes were free from mould with the exception of a very little on two rotary-cut cases, those artificially infected following treatment showing a little more. Chemical examination of the surface of butter packed in Shirlan-treated boxes showed no evidence of salicylanilide. The foil-parchment was effective in preventing mould-growth from penetrating to the surface of the butter, even from the most heavily-infected boxes (Fig.- 6). Extensive damage was caused to the surface of butter to which mould penetrated through the parchment from the interior surface of boxes (Fig- 7)As in the first series of experiments, growth was most extensive in areas adjacent to openings in the box. In some cases profuse growth extended from openings caused by “ sprung ” ends of Saranac boxes and spread over the whole of the interior sides. It was again observed

in this series of experiments that boards taken from “ heart ” closetexture timbers were much less subject to mould-growth than those from sappy, soft-texture timber (Fig. 6). Whilst the Swedish-pine boxes were superior to those made of untreated white-pine in their resistance to mould-growth, they imparted a definitely undesirable wood taint to the surface of the butter.

Discussion. It has been clearly shown that butter-box timber is a source of mould-infection for stored butter. Whilst infected parchment is less important than infected timber as a source of mould, it is readily pierced by mycelium and consequently affords inadequate protection to butter from an infected container. . Butter that has been held in cold storage is very susceptible, to infection from timber during the defrosting process. This is demonstrated by the facts that butter-boxes heavily infected with mould spores showed no growth of mould prior to and on immediate removal

from storage, whilst they developed profuse growth during defrosting. Thus trouble with mould in export butter is not likely to be observed till the butter has reached the retailer. Because of the widespread occurrence of mould spores and the ease with which they are carried by wind, it is impossible to avoid spores on butter-box timber. Under normal defrosting conditions no trouble is experienced from a normal spore load. Yet excessive infection may cause trouble in any circumstances and, what is even more important, there are conditions under which mould-growth from normal spore

load may be favoured. These conditions are (a) the deposition of free moisture on the inner surface of butter-boxes and on the lining parchment-paper ; (&) the admission of air to the space between the butter-box and the parchment ; and (c) the presence of readily available nutrient substances in certain types of timber. The transference of butter from cold stores to chambers held at atmospheric temperatures naturally leads to . the deposition of moisture on the boxes. This deposition is accentuated by high temperature, high humidity, close stacking, and lack of air circulation: Obviously

most trouble is likely to be experienced in summer months. Ideally, cold-stored butter should be defrosted in chambers that can be airconditioned, but this is impracticable under commercial conditions, and, in any case, present losses do not warrant these precautions in temperate climates. It is quite clear that the thickness of timber exercises a distinct influence, | in. white-pine timber developing less mould-growth than | in. That this is not likely to be due to differences in the insulating property of the different thicknesses of timber has been shown by McDowall(s). The more likely explanation is the capacity of the thicker timber to absorb more moisture without becoming soaked. On

removal from a cold store the moisture content of butter-box timber is lower than when admitted to the store. This is illustrated by the fact that the wires on waxed boxes never became so loose as those on unwaxed. During the defrosting process the wood thus absorbs some of the dew as it is formed, and if it can do so at a rate commensurate with that at which the surplus collects there is not likely to be sufficient for mould spores to germinate. The thicker the timber the less free moisture may be expected to accumulate. This may therefore be the explanation of the benefit of using | in. or f in. instead of J in. timber. The admission of air apparently plays an even more important part. It is a significant fact that in these experiments mould-growth was

extremely profuse on the internal surface of boxes to which air was admitted through openings caused by staples, springing from the junction of the sides and ends of the wire-bound boxes. This is probably due to heavy condensation of moisture on the cold surface of the parchment, where, being sheltered from air currents, it is not quickly evaporated. Thus absence of external mould is no guarantee of freedom from internal infection. This emphasizes the great need for so constructing boxes, by using additional staples, clinching their ends, or employing dovetailed pieces of timber, that the sides and ends will remain intact, even when submitted to rough handling.

The type of timber also plays an important part. White-pine timber in the experiments under review developed much more mould than Swedish pine. Whether this is due to a natural fungicide in Swedish pine or to the higher sugar content of white-pine was not investigated. More important, however, than the observation on differences due to species of timber is that “ heart ” —close -white-pine timber scarcely supports mould-growth at all, while the softer sap-wood provides a splendid medium for mould. This is very clearly observed when a side is made of two pieces, one of hard wood, the other of soft (Fig. 6). The use of soft wood must therefore be avoided when dressing timber for butter-boxes. It is also important to observe that rotary-cut timber is much more sensitive, to mould-growth than sawn timber. The results obtained from the treatment of timber with an aqueous solution of the harmless fungicide sodium salicylanilide are most

encouraging. It would not be unreasonable to presume that the o-i per cent, solution with io minutes’immersion used in this experiment would give absolute satisfaction under commercial defrosting conditions, because the two boxes that were not entirely free of mould after treatment were only slightly affected and the experimental conditions were such as to encourage the maximum possible mould-growth. Further experimentation is required to determine the minimum strength of solution and period of dip necessary to prevent mould-growth. (Thereafter the extent to which it can be used depends upon treatment costs.) The results obtained with the use of aluminium-foil parchment show that . this wrapping has yet another advantage besides those which have already been described(4). . • The results obtained with the | in. sawn Saranac container raise the possibility of using this as a standard export type. It combines the advantages of the fin. timber of the sub-standard with the structural advantages of the Saranac type and, provided that the sides are adequately attached to the ends, it gives every indication of being a I reliable and attractive container. ■ ■ Summary. . ■-/ 1./ (1) Moulds originating in butter-boxes may infect the surface layer of butter packed therein and cause extensive damage. ; | (2) A double layer of 28/30 lb. parchment does not prevent ; mould mycelium from penetrating from the internal surface of butteriboxes to the surface of the butter. : (3) Mould-growth on butter-boxes is stimulated by (a) defrosting butter at high atmospheric temperature in air of high humidity; (d) the admission of air to the inner- surface of the box ; (c) the use of sap timber in place of heart timber ; and (d) the treatment of timber by processes which render it more susceptible to mould-growth. (4) Quarter-inch butter-boxes .made from rotary-cut white-pine timber are very susceptible to mould-growth. (5) Standard, fin.' sawn Saranac, sub-standard, and fin. sawn Saranac boxes made of white-pine do not readily develop mould-growth, but they are increasingly susceptible to infection in the order named. (6) The “ springing ” of the sides from the end of Saranac boxes and the admission of air along the sides readily stimulates mouldgrowth on the internal sides of the boxes. (7) Swedish-pine timber, impregnated with wax, is less susceptible to mould-growth than white-pine, but imparts an undesirable timber taint to the surface of the butter. (8) Immersion of butter-box timber in an aqueous solution of sodium salicylanilide promises to be an effective method of preventing mouldgrowth in butter-boxes. (9) Aluminium-foil parchment prevents mould from penetrating from infected boxes to the surface of butter packed therein. Acknowledgments. Dr. F. H. McDowall, of the Institute, staff, examined the surface of the butter for the presence of Shirlan W. S. Three vendors of butterboxes made available the various types of boxes used in the experiments,

and the National Dairy Association provided, free of cost, the alu-minium-foil parchment. Mr. H. Drake photographed the boxes, and Mr. J. W. Smith, Dairy Factory Superintendent, supervised the packing, defrosting, and examination of the butter. References. (1) Vernon, R. : The Deterioration of Dairy-produce by Moulds, N.Z. Journal of Science and Technology, Vol. 15, pp. 237—242, 1934. (2) Neill, J. C. : Prevention of Mould-growth on Box-timber, N.Z. Journal of Agriculture, Vol. 51, pp. 22-26, 1935. (3) General Regulation under New Zealand Dairy Industry Act, 1908. (4) Riddet, Valentine, and McDowall : Lining-materials for Butter-boxes, N.Z. Journal of Science and Technology, Vol. 15, pp. 318-326, 1934. (5) McDowall, F. H. : Rate of Temperature Change in Butter packed in Boxes of Different Types, N.Z. Journal of Science and Technology, Vol. 17, pp. 666-673, 1936.

Type of Box. Non-infected. Artificially infected. Control. Shirlantreated. Untreated. Shirlantreated. Untreated and packed with Foilparchment. Standard white-pine 2 . o 2 2 2 Sub-standard white-pine 2 O 2 2 2 Sawn Saranac white-pine . . ' 2 o 2 2 2 2 O 2 2 2 Rotary white-pine . . .2 O 2 2 2 Sawn Saranac | in. white-pine 2 Q 2 2 o Standard Swedish pine 2 O' 2 2’ 2 0. Sub-standard Swedish pine. . . I I Q I

In all there were used sixty boxes, treated as follows:-

Description. Untreated Control. Treated Shirlan. Untreated inoculated. Treated Shirlan inoculated. ■ Untreated inoculated packed Foil Standard white-pine X o X X XXX " X o XX X XX Sub-standard white-pine XX o X ’ X . XX XX o XX X XXX Sawn Saranac J in. white-pine X o XXX X XXX XX X xxxx x XXX .Rotary - cut Saranac J in. xxxx o xxxx X xxxxx white-pine Ditto xxxxx XX xxxx XX xxxxx Sawn Saranac -g in. white-pine X o X X XX X o X X XX Swedish standard waxed o o X o ■ X o o X X o Swedish sub-standard waxed 0 o o o X

Tabular Presentation of Results of Examination of Butter (Degree of Visible Moulding indicated by Number of Crosses.)