Dear Herman,
If the number is 21 rather than 22 (as the passage you quote indicates), it may refer to the 7 somayajñas + 7 haviryajñas (iṣṭi rites) + 7 pākayajñas, a comprehensive rubrication of Vedic ritual laid out in the Karmāntasūtraappended to the Baudhāyana Śrautasūtra (24.4). Baudhāyana Gṛhyasūtra 1.1.1–12 describes the seven pākayajñas as:
huta: “when [the offering] is made in the fire” (yad dhūyate)
prahuta: “when, after a fire-offering, something is given” (yad dhutvā dīyate)
āhuta: “when, after a fire-offering and a gift, something is received” (yad dhutvā dattvā cādīyate)
śūlagava: “when they skewer pieces of cow-meat on spits and cook them” (
yac chūleṣūpanikṣya[1] gavyāni śrapayanti)
baliharaṇa: “when they scatter food for the gods of the household” (yad gṛhyābhyo devatābhyo ’nnaṃ saṃprakiranti)
pratyavarohaṇa: “when they adopt the low bed from season to season” (yad ṛto ṛtuṃ pratyavarohanti)
aṣṭakāhoma: “when food is prepared during the
ekāṣṭaka rite” (
yad ekāṣṭakāyām annaṃ kriyate)
[2]
The classification into seven here reflects a desire for symmetry with the two types of śrauta rites to yield three 7-member lists — pākayajña, haviryajña, somayajña — as stated in BGParibhāṣasūtra 1.6.22.
For my discussion of this, see:
“Baudhāyanīya Contributions to Smārta Hinduism,” in: Vedic Śākhās: Past, Present, Future. Proceedings of the Fifth International Vedic Workshop, Bucharest 2011, edited by Jan E.M. Houben, Julieta Rotaru & Michael Witzel. Harvard Oriental Series, Opera Minora 9 (Cambridge, Mass.: Harvard, 2016), pp. 591–606.
Warm wishes,
Tim
In Puṟanāṉūṟu 166 a brahmin is described who had "performed to perfection all twenty-one kinds of sacrifices" (trsl. Hart and Heifetz). I am at a loss which 22 sacrifices are referred to here; that is to say, I do not know where to look. I hope someone has a suggestion.
With kind regards, Herman