• Matthew Thorsen
• Bill Metcalfe

Three upcoming Burlington-area concerts are presenting rarities, each of a different order. The University of Vermont Symphony Orchestra will offer a little-known work by Fanny Mendelssohn Hensel, a rare 19th-century female composer whose work rivaled that of her younger brother, Felix Mendelssohn. The Burlington Choral Society will give a concert of 20th- and 21st-century Estonian music, which puts that country's best-known composer, Arvo Pärt, in cultural context. In attendance will be the Estonian ambassador, who is traveling from Washington, D.C., for the event.

And, preceding both of these unusual offerings, Oriana Singers of Vermont will perform Bach's Mass in B-minor. It's not such an unusual choice for this particular group — which has performed it six times, by the estimation of founding director Bill Metcalfe. But the B-minor mass, a landmark of Western music, was rare for its time in that it met neither Catholic nor Lutheran requirements for practical performance as a mass. Perhaps the last composition Bach was working on when he died, it is an expression of spirituality that points beyond religion. Like the other two opportunities to hear great music, it should not be missed.

Yutaka Kono, who has conducted the UVM Symphony since 2011, says he chose Hensel (1805-1847) because he was looking for a female composer to introduce to his 60-member orchestra. From a Women's Philharmonic performance on YouTube, Kono learned of Hensel's Overture in C Major. The work is not always listed among the composer's oeuvre of more than 400 compositions because it was discovered only in 1972, in the Mendelssohn archive in Berlin. Kono had to rent the music from that institution; it's rarely played in the U.S., notes the tuba player from Japan, who also conducts the Burlington Chamber Orchestra.

• Yutaka Kono

Some of Hensel's compositions bore her brother's name, a measure she resorted to after her father began to discourage her pursuit of music as unwomanly. Yet Hensel received as much training as Mendelssohn and, notes Kono, equaled him in melody writing. The Overture has a "really beautiful, songlike melody," he says, that is cleverly contrasted with a fast cello line at one point. The conductor also marvels at a woodwind interlude followed by a "really effective use of flute. It's just a great piece of music."

The UVM Symphony consists of students — some music majors, some not — and community members. Kono was named a finalist for the American Prize in Conducting (college and university orchestra division) for a 2013 concert with the group. He encourages the community to come and see the orchestra precisely because, with no profit motive and the university's support, it can play unusual pieces such as the Hensel.

Smaller orchestras will accompany both choral concerts. The Burlington Choral Society's all-Estonian program draws from one of the most singing-oriented cultures in the world today, according to director Dick Riley. Tossed between Russia and Germany for most of its modern life, Estonia began a four-year "singing revolution" in 1987, staging mass protests in which thousands of Estonians spontaneously belted songs that the Russians had banned. The tradition continues in the annual Estonian Song Festival.

Three festival songs are on the BCS' program, which will be performed at Elley-Long Music Center in Colchester. "It's very stirring stuff," says Riley — "not drums and outward exuberance, as on the American Fourth of July," he adds, "but deeply spiritual and profoundly personal."

• Dick Riley

Even Pärt's orchestral compositions — the program includes two — are "normal for voice," says Riley. A third Pärt work to be performed, "Magnificat," written in 1989, is a haunting piece for unaccompanied chorus that draws from plainsong and the composer's Russian Orthodox background. The first half features a through line on a single note until the chant explodes in a moment of triumph.

BCS' 75 singers will also premiere a work by the contemporary Estonian American composer Lembit Beecher called "An Estonian Diary." Familiar to some Vermont audiences through collaborations with Scrag Mountain Music in Warren, the New York City-based composer grew up speaking both English and Estonian. He based the two-part "Diary" on his two trips to the Baltic country. Riley describes the piece as unique for a large chorus because "most of it is quiet."

Possibly nothing could be further from that eight-minute work than Bach's monumental Mass in B-minor, which clocks in at just under two hours. As Metcalfe avers, "I have no question in my mind" that the work is the greatest ever written for chorus. Scholars have analyzed its status as a compendium of Bach's many stylistic achievements, but, declares the well-read Metcalfe, "the sounds and how they work together — that's miracle enough."

At 30 singers, Oriana is about half BCS' size, and therefore typically oriented toward a different repertoire — a fact that has allowed the two Burlington choirs to coexist peacefully for the past four decades. Metcalfe notes that the Mass "stands up no matter how you do it," but Oriana's size suits it well by not overwhelming the 21-piece orchestra, with approximately one musician to a part.

Six soloists will sing, including soprano Mary Bonhag and tenor Adam Hall. But chorus member Bill Mares, a bass, notes that the B-minor mass is much loved by choruses because it's "two-thirds choral, as opposed to solo, music." Mares, who has sung the work at least three times, describes it as having "that contrapuntal hallmark of Bach, that fugal mode" from which Bach "always brings you home." Even rehearsals of this "transporting, interwoven piece of music" leave him teary, he admits.

Tenor Bill Harwood, who sings in both choruses and invited the Estonian ambassador to the BCS concert — Harwood is a retired cultural attaché in the United States Foreign Service — sums up the two upcoming choral performances. The BCS' is "in a language no one understands, but it's very accessible music in a modern Western idiom," he says. The Oriana concert, by comparison, he says, will be a "spiritual experience" in a church — College Street Congregational — featuring "that Bach exuberance." Luckily, audiences won't have to choose between them.