De-esterification of biomass prior to ammonia pretreatment

A method of pretreating biomass comprising:

• de-esterifying the biomass with an alkali at a concentration from about 2% to 8% alkali in water, to cleave ester linkages to produce de-esterified biomass, wherein the alkali for the de-esterifying the biomass is Ca(OH)2 (lime), KOH, NaOH, or a combination thereof and wherein the alkali to biomass ratio is no greater than 40%, weight/weight;
• annealing the de-esterified biomass to reduce the moisture content to less than about 30%;
• and
• pretreating the de-esterified biomass with ammonia to produce de-esterified ammonia pretreated biomass, wherein the ammonia used in the pretreating step is reduced compared to an amount of ammonia used when pretreating biomass that has not been de-esterified, wherein the ammonia to biomass ratio is between about 0.5:1 to about 1:1,
• the method resulting in an amide concentration in the de-esterified ammonia pretreated biomass ranges from substantially zero mg/g biomass to about 25 mg/g biomass.