Wood sugar and wood molasses

Processes for converting wood into molasses have been known for more than a century. To change cellulose into glucose, high temperatures and pressures are required when dilute acids are used. With concentrated acids the process can be carried out at room temperature, but the percentage of unrecovered acid makes the cost very high. Hemicellulose is more easily converted into sugars. The hemicellulose from hardwood (e.g., maple and beech) yields a high percentage of 5-carbon sugars, while hemicellulose from softwood (e.g., pine and fir) yields a fifty-fifty mixture of 5-carbon sugars and 6-carbon sugars. Ruminants can assimilate both types of sugars, whereas the 5-carbon sugars are less available to monogastric animals. The Madison wood-sugar process, which consists in hydrolysing cellulose into simple sugars, is one of the more economical of the many methods developed for this purpose. It involves continuous pumping of a spray of hot 0.5-0.6% sulphuric acid on chips or sawdust heated in a digester to 150 C at the start and gradually increased to 185 C. After removal from the digester the sugar solution is cooled to 138 C and neutralized with lime. The resulting sugar solution contains 5-6% simple sugars and is concentrated to a syrup for feeding. One ton of wood will yield about 0.5 ton of sugars. The syrup has a bitter taste, but this does not seem to make the molasses less palatable to cattle. The syrup can be used for cattle in the same way as sugar-cane molasses (see MOLASSES). Sugars from softwood can constitute up to 20% of poultry rations in substitution for the same percentage of grain. 

A newer related procedure is the solubilization of hemicellulose from wood by steam during the manufacture of hardboard. This process is economical as it does not require chemicals. The hemicellulose sugars are concentrated or spray-dried and sold as animal feed under the name wood molasses. For ruminants wood molasses is roughly equal to sugar-cane molasses. It can be included up to 5% in diets for monogastric animals. Above that level the energy value of wood molasses declines as the amount in the diet is increased. High levels of wood molasses in diets for monogastric animals cause digestive disorders. 

					As % of dry matter
				DM	CP	CF	Ash	EE	NFE	Ca	P	Ref
Wood molasses,
acid process				63.6	1.1	0.0	6.0	0.3	92.6	2.80	0.09	350
Wood molasses,
steam process				65.0	0.8	1.0	9.2	0.3	88.7	1.23	0.12	"

References

202, 350