Bacterial oak: drying problems

Purchased by U. S. Department of Agriculture, Forest Service, for official use. James C. Ward David A. Groom

wetwood that is more prevalent in red oaks than in Abstract white oaks (21). Kiln-dried 4/4 northern red oak lumber was pro­ Bacterially infected heartwood in oak can appear cessed into millwork and yields were evaluated with sound and without dark discolorations. But green lum­ respect to 1) normal and bacterially infected heartwood ber containing bacterial heartwood is more prone than and 2) mild and accelerated kiln schedules. The pre­ normal, noninfected oak to develop excessive amounts sence of bacterially infected heartwood reduced yields of drying defects even when kiln-dried by relatively from rough, dry lumber because of deep surface checks, mild conventional schedules (18, 19, 20). Volume losses honeycomb, and ring failure. Volume losses from bac­ from kiln-drying bacterial oak are principally due to terial oak lumber greatly increased with accelerated deep surface checks, honeycomb, and ring failure. kiln-drying. Estimations were made of added produc­ Under normal conditions, commercial kiln operations tion costs in the rough mill that were related to lumber will generally lose 2 to 3 percent of their oak lumber to volume losses from drying defects. When compared to honeycomb. mild-dried normal oak, added costs were higher by 23.2 percent for fast-dried bacterial oak, 6.6 percent for mild- Prior to 1972, when the first reports of bacterial oak dried bacterial oak, and 5.6 percent for fast-dried nor­ were published (18, 19), any unexpected and excessive mal oak. Consequently, accelerated kiln-drying of occurrence of drying defects was attributed to natural green oak lumber is feasible for boards with normal variability in the inherent properties of oak. It was long heartwood, but not for boards with bacterial heartwood known that the ease of kiln-drying oak without defects which must be dried under mild schedules. Kiln-drying could vary among regions, among trees within an area, of oak can be optimized by segregating bacterial oak and even among different boards from within the same from normal oak on the lumber green chain and drying tree (17). Now it is known that many examples of unex­ each sort under its appropriate schedule. An accurate pected drying defects in oak can be associated with system for commercial presorting of bacterial oak does trunk infections by anaerobic bacteria; the infections not exist, and the possibilities for developing one are weaken but do not decay or necessarily discolor the discussed. heartwood (18, 21). In this paper we report results from an exploratory study that was initiated primarily to determine how the

In recent years the term bacterial oak has become increasingly familiar to the hardwood lumber industry, The authors are, respectively, Forest Products Tech­ particularly those segments concerned with the drying nologist, USDA Forest Serv., Forest Prod. Lab., P.O. Box 5130, and processing of oak for flooring, furniture, and mill- Madison, WI 53705; and Director of Manufacturing Services, Pennsylvania House Furniture, Lewisburg, Pa. They are grate­ work. (Industry sometimes employs the terms “sour, ful to Gary Homberg, Millfab, Inc., for use of his plant facilities sick, or rancid oak” because of odors ranging from to convert the kiln-dried lumber into millwork. The Laboratory strong vinegar and rancid butter to goat odors. These is maintained at Madison, Wis., in cooperation with the Univ. of Wisconsin. The use of trade, firm, or corporation names in this odors are due to a mixture of volatile fatty acids, namely publication is for the information and convenience of the reader. acetic, propionic, butyric, valeric, and caproic acids Such use does not constitute an official endorsement or approval (22)). by the U.S. Dept. of Agriculture of any product or service to the exclusion of others which may be suitable. This paper was re­ Bacterial oak refers to heartwood that has been ceived for publication in December 1981. infected or colonized by anaerobic bacteria while still in © Forest Products Research Society 1983. the living tree (18) and can be considered a form of Forest Prod. J. 33(10):57-65.

FOREST PRODUCTS JOURNAL Vol. 33, No. 10 57 presence of bacterial heartwood and kiln schedules will Wisconsin. All logs were sound, 8 to 9 feet long, with an affect the yields of millwork from 414 northern red oak average scaling diameter (small end inside bark) of 13 lumber. Although previous studies were concerned with inches. Thirty-four logs contained heavy infestations of the effect of bacterial heartwood and drying conditions bacterial heartwood, indicated by sour, rancid odors and on defect formation in oak lumber, there was no indi­ sometimes by the presence of ring shake. The remaining cation of how the yield of machined products would be 74 logs contained mostly normal heartwood. affected. In two studies (9, 19) at the Forest Products The logs were sawed into 1-118-inch-thick boards Laboratory (FPL), the magnitude of drying defects was that were marked either as normal or bacterial de­ determined by crosscutting sections from dried boards pending on the log source and odor of the boards. The and then calculating the volume of visible honeycomb, lumber was graded on the green chain according to surface checks, and ring failure. A third study with 414 National Hardwood Lumber Association Rules (11). California black oak (20) reported lumber degrade Drying sample. – For the drying tests, 486 boards losses from bacterial heartwood that were based on the (2,616 board feet (BF)) of No. 1 Common and Better amount of collapse, checks, and ring failure visible on lumber were selected from the green lumber. Each the surface and ends of rough boards after kiln-drying. board was numbered and marked as either normal or Converting dried lumber into millwork provides a rela­ bacterial, depending on the major type of heartwood tively thorough method for ascertaining the effect of present. The heartwood was classified on the basis of its drying defects on yield of machined products. Figure 1 characteristic fatty acid odor which was evaluated with illustrates how honeycomb can be a more serious defect the human nose. A board was considered bacterial if it in millwork than in a surfaced board. emitted the following fatty acid odors on both sides or at A secondary study objective was to obtain infor­ least along the length of one face: strong vinegar (acetic mation on wood properties that can lead to detection of acid) odor, rancid (butyric and valeric acid) odors, or bacterial heartwood in green oak so that defect-prone goat (caproic acid) odor. Portions of some bacterial boards can be segregated from normal lumber before boards emitted aromatic fruity odors of apricot and drying. Each board sort can then be dried under condi­ apple which suggests that the above fatty acids had tions that ensure minimal wood losses with optimal use become esterified by some undetermined mechanism. of energy. Just as there is a need to dry bacterial oak Normal boards emitted a characteristic oak odor, some­ under mild conditions to reduce drying defects, there is times with a faint trace of acetic acid odor which will also a need to accelerate the kiln-drying of normal, occur in noninfected heartwood (22). Twenty-four noninfected oak to reduce energy requirements and boards (12 normal and 12 bacterial) were taken from lumber inventory (15). This cannot be done if bacteri­ this selection, and a 30-inch-long kiln sample together ally infected oak is present in the charge. No technique with end-matched moisture content (MC) sections and is currently available for commercial segregation and sections for auxiliary samples were then cut from each presorting of large volumes of green oak lumber. board (Fig. 2). Materials and methods The remaining 2,504 BF of green lumber was sorted Sample material and loaded into two experimental dry kilns in a single operation. Normal and bacterial boards were dis­ Logs and green lumber. – A total of 108 logs from tributed throughout each kiln charge during loading as recently felled northern red oak (Quercus rubra L.) trees indicated in Table 1. The proportion of bacterial oak to were selected from several logging sites in south-central normal oak was 33 percent in the mild charge and 39 percent in the accelerated charge. Each kiln charge was approximately 4 feet high by 4 feet wide and 16 feet long. Stickers, 1-114 inch wide by 314 inch thick, were spaced 2 feet apart along the length of the charge. Auxiliary samples. – Board sections end-matching the 24 kiln samples (Fig. 2) were used to determine wood

Figure 2. – Diagram of how red oak boards were cut into samples forwood propertydeterminations. End-matched sec­ tions were used for 1) initial MC determination of kiln sample Figure 1. – Millwork (top) and surfaced board (bottom) from (1- to 2-in. long grain); 2) determining growth rate, pulsed- northern red oak lumber that contained bacterial heartwood current resistance, MC, and density; 3) microbial isolations; and honeycombed during kiln-drying. and 4) pH measurements.

58 OCTOBER 1983 properties and microbial condition of the green heart­ temperature, was patterned after schedules used in wood. After drying tests were completed, an additional previous FPL studies for careful drying of bacterially sample of 19 northern red oak boards was collected from infected oak (9, 20). Average air velocities were main­ the same mill that supplied the drying sample. These 19 tained across the lumber at 445 feet per minute (fpm) for boards were collected at a later date to determine if accelerated drying and 405 fpm for mild drying. green MC could be accurately measured with a portable Each kiln charge used 12 kiln samples, 6 on each radiofrequency (RF) moisture meter. side, which were weighed daily to measure moisture loss. It was intended that six normal samples and six Drying procedure bacterial samples be placed in each kiln charge. Later results from microbial tests of end-matched wood sec­ Both kiln charges started drying on the same day. tions showed that 7 of 12 samples in the accelerated One charge was dried under an accelerated schedule charge were bacterially infected and only 5 were and the other under a mild schedule (Table 2). Both normal. charges were dried to a target MC of 8 percent. The initial dry-bulb temperature of 125°F was selected for Evaluation of drying losses the accelerated schedule to provide a severe drying test Shrinkage. – The width at midlength of each board for oak. Henderson (6) and Rietz (13) used an initial was measured to the nearest 1/10 inch before and after dry-bulb temperature of 120°F for accelerated drying of drying. Shrinkage was calculated as the loss in surface 414 red oak, but more recent reports (10, 15) recommend area of each board from green to approximately 8 per­ 115°F. The mild schedule, using 105°F initial dry-bulb cent MC.

TABLE 1. – Volume distribution of green 414 northern red oak boards by lumber sort and grade and by kiln charge.

aBF = board feet.

TABLE 2. – Experimental kiln schedules for 4/4 northern red oak.

FOREST PRODUCTS JOURNAL Vol. 33, No. 10 59 Drying defects. – From results of previous studies mash and semisolid trypticase-soy agar and on sodium (9, 19, 20) it was assumed that a minimal amount of caseinate agar for evaluation of microbial odor pro­ drying defects should develop only in normal heartwood duction. kiln-dried under a mild schedule. Consequently, the Moisture content. – Gravimetric methods (10, 12) normal board sort dried under the mild schedule pro­ were used to determine the MC of 24 kiln samples and vided the basis (or control) for estimating excess losses small end-matched wood specimens. MC values are due to presence of bacterial heartwood and accelerated expressed as a percentage of the ovendry weight of the drying. wood. The kiln-dried lumber was sorted so that boards An additional sample of 19 green northern red oak were divided according to the following classifications: boards (8 normal and 11 bacterial), was measured for 1) mild-normal heart or control pile, 2) mild-bacterial MC with an experimental RF moisture meter (Delm­ heart, 3) accelerated normal heart, and 4) accelerated- horst Instrument Co., Boonton, N.J.). This type of meter bacterial heart. All four groups were hauled to a nearby differs from the direct current resistance-type meters millwork plant where the lumber was processed into that are not capable of yielding qualitative readings at millwork. wood moisture levels greater than 30 percent (7). Den­ In the rough mill each lumber sort was separately nis and Beall (4) report that this model RF meter re­ ripped and cut into sized stock which was machined by sponds to a wide range of moisture levels and found its moulders into millwork. The type of millwork produced operation to be independent of species and density. In in this study, and the dimensions of the corresponding this study a total of 60 points were measured; sections sized stock, are outlined in Table 3. All pieces of sized were crosscut at the points of measurement, weighed, stock and millwork were tallied after rough mill and and ovendried for determination of actual MC to be moulder operations. The volume of sized stock produced compared with RF meter readings. in the rough mill was compared with the volume of Other properties. – Growth rate, pulsed-current rough-dried lumber when calculating yields. Millwork resistance, specific gravity (SG), and density were mea­ yields were based on the number of pieces that passed sured on the same end-matched specimens used for MC final inspection. Rough mill production times for each determination in board section 2 (Fig. 2). The growth lumber sort were recorded. rate, expressed in rings per inch, was determined by Green wood characteristics averaging the measurements from both ends of the Microbial. – These tests were concerned with re­ specimens. lating micro-organisms to drying defects and abnormal Resistance to a pulsed electric current was mea­ wood odors. Board sections end-matching the kiln sured with a Shigometer (a portable ohmmeter manu­ samples (Fig. 2) were split radially; then five wood chips factured by Northeast Electronics Corp., Concord, N.H.) were aseptically removed and placed in tubed culture by inserting needle electrodes, spaced 112 inch apart, media prepared under standard procedures (16). Two into the end grain of the specimens to a depth of 1/4 inch. tubes containing potato mash and thioglycollate broth This meter measures differences in resistance which are were incubated under hydrogen and carbon dioxide influenced by the concentration and mobility of ions in atmospheres in an (BBL Gas Pak) anaerobic system the green wood. Meter readings are not effective in wood (Bioquest, Div. of Becton, Dickinson and Co., Cock­ that has dried below the fiber saturation point where eysville, Md.) for detection of obligate anaerobes. The ion mobility greatly decreases. three remaining tubes containing semisolid trypticase­ SG was determined on the green volume and oven- soy agar, semisolid potato dextrose agar, and a solid dry weight basis, with volume determined by water malt agar slant were incubated aerobically. Repre­ immersion. Wood density was also calculated. sentative cultures of micro-organisms recovered from The pH was determined on wood shavings (green the initial isolations were later reinoculated in potato condition) moistened enough to be measured using a glass electrode and electronic pH meter. Shavings were obtained with an electric drill from the No. 4 board sections in Figure 2, side-matched to wood used for TABLE 3. – Types of millwork in the final-product group and microbial tests, and were moistened with distilled water corresponding dimensions of sized stock from which (recently boiled and cooled). the millwork was machined on the moulders. Sized stock dimensionsa Results and discussion Type of millwork Width Length Drying (in.) (in.) Cove 1 Random lengthb The accelerated schedule reduced total kiln-drying stop 1-518 84 time by 11 days (from 26 to 15) or 40 percent (Fig. 3). Threshold 4 33 and 37-112 Within each kiln charge, boards with bacterial heart­ Jamb 4-718 80 Header 4-718 36, 48, 60, and 72 wood dried to 8 percent MC within the same time period Stiles and rails 2-3/8 10, 11-112, 13, 14-112, as normal boards. These results agree with previous 16, 19, 22, and 28 drying studies of northern red oak (9, 19), California aSized stock was ripped and then crosscut from 4/4 rough dry boards, 8 to 9 ft. black oak (20), and American elm (2) in that bacterial long. and normal heartwood dried at similar rates. (Reports bMinimum length of 36 in. with 6-in. increments to maximum length of the board. from industrial sources indicate some charges of bac­

60 OCTOBER 1983 tissue, the compound middle lamella contains relatively large amounts of pectin and is probably weakened by the enzymatic action of Clostridium and associated micro-organisms found in bacterial oak. Microscopic examination of honeycomb and ring failure in the kiln- dried oak samples revealed that these ruptures com­ monly occurred in compound middle lamellae between ray and fiber tissue or between earlywood and latewood of the previous growing season. Apparently, pectin- degrading bacteria are a factor in the reduced ability of bacterial oak to withstand shrinkage stresses during kiln-drying. The characteristic sour and rancid odors in defect- prone oak are due to a mixture of volatile fatty acids which were reproduced in vitro by growing clostridia isolated from the samples of this study in potato-mash media. When these same strains of clostridia were grown anaerobically on sodium caseinate agar, the Figure 3. – Comparative drying curves for 4/4 northern red oak lumber sorts of normal and bacterial heartwood dried prevalent odor was reminiscent of brick cheese rather under accelerated and mild schedules in experimental kilns at than bacterial oak. Abe and Minami (1) were able to the U.S. Forest Products Laboratory. trace abnormal fatty acid odors in the tropical wood Gonystylus bancanus (Miq.) Kurz to bacterial metab­ olism of extractives and hemicelluloses. All wood isolates with a fruity odor came from terial oak, particularly from bottomlands, require 10% bacterial heartwood, but aerobic cultures consistently to 25% longer kiln-drying time.) yielded a nondecay fungus Paecilomyces varioti Banier Microbial influences along with facultative bacteria. This fungus was also Isolation data in Table 4 show a strong association isolated, along with facultative bacteria, from normal of drying defects in the kiln samples with the presence of oak without a fruity odor (Table 4). In previous FPL anaerobic bacteria, particularly obligate anaerobes in studies (3, 18, 19), P. varioti has occasionally been iso­ the genus Clostridium. These results agree with pre­ lated from heartwood in oak logs and trees; it appears to vious FPL studies (9, 18, 19, 20) where clostridia were occur in, or near, discolored wood that can be traced to found to be associated with honeycomb and ring failure injuries of the roots or lower stem. P. varioti is capable of in oak. Schink, Ward, and Zeikus (14) found that Clos­ rapid growth and spread through bacterial heartwood of tridium isolated from wetwood can degrade pectin in oak under aerobic conditions. P. varioti, when growing xylem tissue, but not cellulose and lignin. In xylem in bacterial oak, may be responsible for esterification of

TABLE 4. – Comparison of occurrence of drying defects in northern red oak kiln samples with heartwood type and odor, kiln schedule, and occurrence of bacteria and fungi in clear wood chips isolated from end-matched hoard sections.

FOREST PRODUCTS JOURNAL Vol. 33, No. 10 61 fatty acids resulting in production of the aromatic fruity advantage to drying green bacterial oak under mild kiln odors. schedules because yields for this material (Table 5) were Viable bacteria cannot always be isolated from only 5 percent less for sized stock in comparison with defect-prone oak with sour and rancid odors even slow-dried normal oak. Corresponding losses for fast- though bacteria are responsible for these heartwood dried normal oak were slightly greater than losses for characteristics. Bacterial populations will shift to adja­ slow-dried bacterial oak. cent zones of noninfected heartwood during the life of Greatest reductions in yield occurred during the the tree, and the remaining bacteria may not survive in processing of rough lumber into sized-stock when dry­ spore form. Also, obligate anaerobes are not always ing defects, together with natural defects (knots, over­ able to rapidly sporulate and survive the aerobic atmos­ grown bark, etc.), were eliminated as waste. Clear wood pheres that develop in logs and green lumber. cuttings from slow-dried normal boards had the small­ Lumber volume losses est amount of drying defects, and yields from this sort could be used to compare the effect of bacterial heart­ Shrinkage. – Lumber volume losses due to shrink­ wood and accelerated drying on drying losses for other age in width of the oak boards were 1 percent greater for sorts. bacterial heartwood than for normal heartwood (Table 5). The drying schedule used, mild or accelerated, made Honeycomb and ring failure occurred only in bac­ essentially no difference in the shrinkage of either nor­ terial heartwood and not in normal heartwood. With mal oak or bacterial oak. Greater shrinkage of bacterial accelerated drying, honeycomb was much more preva­ heartwood was previously observed for California black lent in bacterial heartwood than was ring failure. How­ oak (20). This report also noted shrinkage differences ever, with mild drying the frequency and magnitude of between air-dried and kiln-dried stock where kiln- honeycomb was greatly reduced, but ring failure was drying oak green from the saw results in greater shrink­ not similarly reduced. In previous studies with bacterial age of both normal and bacterial heartwood than occurs oak (9, 19, 20) it was also observed that milder drying if the stock is air-dried before kiln-drying. conditions did not reduce ring failure to the same degree as honeycomb. Ring failure generally develops in Shrinkage differences between air-dried and kiln- boards sawed from logs with ring shake, suggesting that dried oak and between normal and bacterial heartwood ring failure is an incipient form of ring shake that did can be explained by the theory of compression set, pro­ not rupture in the tree. Devine (5) concluded that ring viding SG and growth ring orientation are similar. shake is due to an inherent weakness in the wood and Compression set develops within the core of boards should not be blamed on the kiln-drying operation. during the intermediate stages of drying when the MC of the core is above the fiber saturation point and being Moulder rejects. -Whensized stock was processed compressed by a drier shell that is shrinking. Elevating into millwork, the number of pieces of millwork that drying temperatures weakens the moist core. McMillen were rejected as suitable for a final product (Table 6) (8) demonstrated with red oak that the higher tempera­ showed relatively little difference among bacterial and tures of kiln-drying will cause greater compression set, normal wood sorts. More moulder rejects came from with significantly greater shrinkage than the lower fast-dried bacterial stock, primarily because of splits temperatures of air-drying. and shelling associated with surface checks, honey­ comb, and ring failure. Lumber product losses. – Accelerated drying of bacterial boards caused the greatest loss in volume of The relative amounts of moulder rejects (Table 6) lumber that could potentially be used for millwork are probably less than might be expected at many com­ (Table 5). When compared with slow-dried normal mercial operations. Care was taken at the rough mill in heartwood, yields of fast-dried bacterial heartwood this study to eliminate all traces of honeycomb and ring were 25 percent less for sized stock. There is a definite failure from the clear lumber cuttings. This effort re-

TABLE 5. – Shrinkage losses and yield of sized stock for 4/4 northern red oak, No. 1 Common and Better grade lumber.

62 OCTOBER 1983 quired additional cutting times that would not always Additional costs from drying defects in fast-dried be practical under more normal operating conditions. and bacterial oak were estimated only up to production The point here is that kiln-dried bacterial oak will have of sized stock in the rough mill. Because of the milling more drying defects with greater losses in volume of and machining procedures employed, a comparison of final product than normal oak. sized product yields with associated production costs is Added production costs sufficient for meaningful interpretation of results. The calculations in Table 7 show the utility value of Presorting possibilities No. 1 and Better oak is diminished by the presence of Measurements of the six wood properties inves­ bacterial heartwood and by accelerated kiln-drying. tigated in this study are presented in Table 8. Except for The accelerated schedule reduced kiln-drying costs by MC, none of these properties appear to be useful for $12 per thousand board feet (MBF), but the savings detecting bacterial heartwood in green oak lumber. The were offset by increased drying defects. Rough mill distinctive odor of bacterial oak was not measured, but production costs were greatly increased with acceler­ appears to be an excellent prospect for presorting oak. ated drying of bacterial boards because of losses in yield Moisture content. – A frequency distribution of of sized stock due to defects and the increased processing MC values for all samples taken during the course of time required to produce defect-free stock. With mild this study (Fig. 4) shows that 58 percent of the bacterial kiln-drying the defects in bacterial boards resulted in a samples had green MC values within the range of nor­ loss of $33/MBF which is 3.6 times less than the mal heartwood values. If this distribution represented $118/MBF loss for fast-dried bacterial boards. Acceler­ the entire kiln charge, then segregating boards with ated drying also increased volume losses for lumber MC greater than 83 percent could result in three- with normal heartwood, but the increased costs were fourths of the bacterial boards and one-third of the only one-fourth of the costs for fast-dried bacterial lum­ normal boards being placed in a sort for mild drying. ber in the same charge. These added cost data demon­ The remaining boards, i.e., those with less than 83 strate the existence of an oak processing problem that percent MC, could then be dried under conventional, requires more attention than is being given by the and possibly accelerated, conditions with a reduced risk hardwood industry. of developing costly defects.

TABLE 6. – Yield of red oak millwork from sized stock.

TABLE 7. – An estimate of comparative production costs in the rough mill for processing sized stock from normal and bacterial board sorts of 414 northern red oak lumber kiln-dried under mild and accelerated kiln schedules.

FOREST PRODUCTS JOURNAL Vol. 33, No. 10 63 TABLE 8. – Variation of wood properties of northern red oak in the green condition according to type of heartwood.

study. However, growth rate cannot be expected to be useful for presorting because the pertinent bacterial infections develop in the heartwood and not in the cambium where the annual rings are first formed. Density values were also similar for both normal and bacterial oak heartwood, indicating that board weights cannot be used for presorting green oak. The mean SG of bacterial heartwood tends to be slightly lower than for normal heartwood, but the generally higher MC of bacterial heartwood appears to offset differences in SG without contributing to a noticeable increase in weight. Average values for pulsed-current resistances were somewhat lower for bacterial oak, but there was con­ siderable overlap with resistances of normal oak. These data for northern red oak were similar to resistance data for California black oak (20), and it is unlikely that pulsed-current resistances can be employed for accurate presorting of oak. Figure 4. – Frequency distribution of moisture contents (green condition) for normal and bacterial heartwood from northern red oak.

High MC levels prompted exploratory use of the RF moisture meter for measuring MC in green oak. Results plotted on the graph of Figure 5 show a weak relation­ ship between RF meter readings and actual MC. Also, there is considerable overlap of MC values for normal and bacterial heartwood. Until a more precise moisture meter can be developed, there is little indication that green MC will be a possible presorting characteristic for bacterial oak. Other properties. – The remaining wood properties of Table 8 cannot be used to segregate bacterial oak Figure 5. – Response of a portable radiofrequency moisture from normal oak. Growth rates were similar for both meter to average moisture content of green 4/4 northern red normal and bacterial heartwood samples used in this oak.

64 OCTOBER 1983 The pH of bacterial heartwood tends to be more Since a good detection method for bacterial oak does not acidic than normal heartwood which is already quite exist, all wood must be dried conservatively to minimize acid (Table 8). The considerable overlap of bacterial and loss if any sour, rancid odors are detected in the lumber normal oak pH values indicates that pH measurements stock. will not be highly accurate for segregating bacterial oak with available techniques. Literature cited 1. ABE, Z., and K. MINAMI. 1976. [Ill smell from the wood of Gonystylus Abnormal odors. – Sour and rancid odors are not bancanus (Miq.) Kurz. I. Source of ill smell. II. Smelling compo­ normal for oak and represent the most reliable charac­ nents.] J. Jap. Wood Res. Soc. (Mokuzai Gakkaishi) 22(2):119-122. teristic or property of heartwood that is prone to develop [In Jap.]. drying defects. As previously discussed, these odors are 2. BOONE, R.S., and J.C. WARD. 1977. Kiln-drying lumber from Amer­ ican elm trees killed by Dutch elm disease. Forest Prod. J. 27(5):48­ due to a mixture of volatile fatty acids produced by 50. anaerobic bacteria. This suggests that the most accu­ 3. BULGRIN, E.H., and J.C. WARD. 1968. Factors contributing to rate and reliable method for presorting bacterial oak heartwood-boundary stain in living oak. Wood Sci. 1(1):58-64. 4. DENNIS, J.R., and F.C. BEALL. 1977. Evaluation of a new portable may require measurement of these fatty acids. Since the radiofrequency moisture meter on lumber with drying gradients. early work by Zinkel, Ward, and Kukachka (22), gas Forest Prod. J. 27(8):24-29. chromatography has been used at FPL to measure fatty 5. DEVINE, J. 1954. Exactly how much degrade is your kiln responsible acids to verify identification of bacterial oak. This for? Natl. Hardwood Mag. 28(4):23-24. 6. HENDERSON, H.L. 1951. The Air Seasoning and Kiln Drying of method is time consuming, requiring steam distillation Wood. 5th ed. 364 pp. Published by the author, Albany, N.Y. of wood samples, and is not applicable to production line 7. JAMES, W.L. 1975. Electric moisture meters for wood. USDA Forest detection of bacterial oak. Bacterial oak, when green, Serv. Gen. Tech. Rept. FPL-6, 28 pp. Forest Prod. Lab., Madison, Wis. can be accurately and rapidly detected with the human 8. MCMILLEN, J.M. 1955. Drying stresses in red oak. Forest Prod. J. nose, but sensitivity varies by individuals. Then too, the 5(1):71-76. human nose soon loses sensitivity during prolonged 9. , J.C. WARD, and J. CHERN. 1979. Drying procedures for bacterially infected northern red oak. USDA Forest Serv. Res. Pap. exposure to the odors of green oak in a mill. Research at FPL 345, 15 pp. Forest Prod., Lab., Madison, Wis. FPL is presently concerned with investigations of faster 10. , and E.M. WENGERT. 1978. Drying eastern hardwood techniques �or measuring fatty acids in oak. lumber. USDA Agri. Handbk. No. 528,104 pp. U.S. Govt. Printing Office, Washington, D.C. Conclusions 11. NATIONAL HARDWOOD LUMBER ASSOCIATION. 1978. Rules for the measurement and inspection of hardwood and cypress lumber. 1. Bacterial heartwood in all grades of oak lumber National Hardwood Lumber Assoc., 115 pp. Box 34518, Memphis, is more prone than normal wood to develop surface Tenn. 38134. 12. RASMUSSEN, E.F. 1961. Dry kiln operators manual. USDA Agri. checks, honeycomb, and ring failure when kiln-dried Handbk. No. 188, 197 pp. U.S. Govt. Printing Office, Washington, green from the saw. Drying defects associated with D.C. bacterial heartwood increase volume losses when the 13. RIETZ, R.C. 1970. Accelerating the kiln-drying of hardwoods. South. lumber is processed into millwork. Added production Lumberman 221(2741):19-22, 24. 14. SCHINK, B., J.C. WARD, and J.G. ZEIKUS. 1981. Microbiology of costs will be greatest in the rough mill where drying wetwood: importance of pectin degradation and Clostridium species defects influence yields of sized stock to be used in final in living trees. Appl. Environ. Microbiol. 42(3):526-532. production of millwork on moulders. 15. SIMPSON, W.T. 1980. Accelerating the kiln drying of oak. USDA Forest Serv. Res. Pap. FPL 378. 9 pp. Forest Prod. Lab., Madison, 2. When bacterial heartwood is present in a charge Wis. of green oak lumber, losses from any sort of drying 16. SOCIETY FOR AMERICAN BACTERIOLOGISTS. 1957. Manual of Micro­ acceleration will be exhorbitant. Accelerated kiln- biological Methods. 315 pp. McGraw Hill Book Co., Inc., New York. 17. TORGESON, O.W. 1951. What precautions will minimize seasoning drying is feasible only for green oak with normal heart­ defects in the kiln drying of green oak lumber? Forest Prod. Lab. wood and not for bacterial oak which must be dried Rept. No. D1769-11, 2 pp. Madison, Wis. under mild conditions. Satisfactory drying conditions 18. WARD, J.C. 1972. Anaerobic bacteria associated with honeycomb and ring-failure in red and black oak lumber. (Abstr.) Phytopathol­ for green bacterial oak require, initial dry-bulb tem­ ogy 62(7):796. peratures of 90°F or less with relative humidity condi­ 19. , R.A. HANN, R.C. BALTES, and E.H. BULGRIN. 1972. tions greater than 60 percent. Generally, this means Honeycomb and ring-failure in bacterially infected red oak lumber that bacterial oak should be predried (either by air- after kiln drying. USDA Forest Serv. Res. Pap. FPL 165, 37 pp. Forest Prod. Lab., Madison, Wis. drying or in low-temperature forced-air kilns) to under 20. , and D. SHEDD. 1979. California black oak drying prob­ 25 percent average MC and then kiln-dried to minimize lems and the bacterial factor. USDA Forest Serv. Res. Pap. FPL loss. 344, 15 pp. Forest Prod. Lab., Madison, Wis. 21 , and J.G. ZEIKUS. 1980. Bacteriological, chemical and 3. For mills that are troubled with bacterial oak, physical properties of wetwood in living trees. In: J. Bauch, Natural an ideal drying program would be to identify and seg­ variations of wood properties. pp. 133-166, Mitt. Bundesforschung­ regate bacterial boards from normal lumber on the sanstalt f. Forst- und Holzwirtschaft, Hamburg, Nr. 131. Hamburg: Max Wiedebusch. green chain. Each board sort, normal and bacterial, 22. ZINKEL, D.F., J.C. WARD, and B.F. KUKACHKA. 1969. Odor prob­ would then be dried under the appropriate schedule. lems from some plywoods. Forest Prod. J. 19(12):60.

FOREST PRODUCTS JOURNAL Vol. 33, No. 10 65