A system comprising: a memory storing processor-executable process steps; a processing unit to execute the processor-executable process steps to cause the system to: acquire (S610) a domain grammar (130; 350; 930; 1030); determine (S640) an interpolated grammar based on the domain grammar and a base grammar (320; 940; 1040); determine (S650) a delta domain grammar based on the interpolated grammar and an augmented first grammar stored prior to acquisition of the domain grammar, the augmented first grammar generated based on the base grammar and allowing for insertion of an out-of-vocabulary class ; determine a first out-of-vocabulary class based on the domain grammar and the base grammar; insert the first out-of-vocabulary class into a composed transducer composed of the augmented first grammar and one or more other transducers to generate an updated composed transducer , where the composed transducer is composed (S440) and stored (S450) prior to acquisition of the domain grammar; compose (S660) the delta domain grammar and the updated composed transducer; and apply (S670) the composition of the delta domain grammar and the updated composed transducer to an output of an acoustic model. a memory storing processor-executable process steps; a processing unit to execute the processor-executable process steps to cause the system to: acquire (S610) a domain grammar (130; 350; 930; 1030); determine (S640) an interpolated grammar based on the domain grammar and a base grammar (320; 940; 1040); determine (S650) a delta domain grammar based on the interpolated grammar and an augmented first grammar stored prior to acquisition of the domain grammar, the augmented first grammar generated based on the base grammar and allowing for insertion of an out-of-vocabulary class ; determine a first out-of-vocabulary class based on the domain grammar and the base grammar; insert the first out-of-vocabulary class into a composed transducer composed of the augmented first grammar and one or more other transducers to generate an updated composed transducer , where the composed transducer is composed (S440) and stored (S450) prior to acquisition of the domain grammar; compose (S660) the delta domain grammar and the updated composed transducer; and apply (S670) the composition of the delta domain grammar and the updated composed transducer to an output of an acoustic model. acquire (S610) a domain grammar (130; 350; 930; 1030); determine (S640) an interpolated grammar based on the domain grammar and a base grammar (320; 940; 1040); determine (S650) a delta domain grammar based on the interpolated grammar and an augmented first grammar stored prior to acquisition of the domain grammar, the augmented first grammar generated based on the base grammar and allowing for insertion of an out-of-vocabulary class ; determine a first out-of-vocabulary class based on the domain grammar and the base grammar; insert the first out-of-vocabulary class into a composed transducer composed of the augmented first grammar and one or more other transducers to generate an updated composed transducer , where the composed transducer is composed (S440) and stored (S450) prior to acquisition of the domain grammar; compose (S660) the delta domain grammar and the updated composed transducer; and apply (S670) the composition of the delta domain grammar and the updated composed transducer to an output of an acoustic model. <EOS>